# 2008 Beetle Coupe Error Code Adventures!



## addicted2sp33d (Jun 5, 2009)

So my wife's 2.5L Beetle recently started throwing codes... somehow it knew that registration and smog inspection is due in August! 

Want to bounce some ideas off the geniuses around here. 

Caveat - I'm not a certified tech by any means, but I am mechanically savvy and can mostly tackle anything that doesn't require an engine hoist or a fancy-pants computer. 
I have access to a OBD-II Diagnostic tool, but it is not a fancy VCDS or anything like that. I can only read static codes and Freeze Data after the Code happens. I cannot see pending codes or live data. 
I might sound like I know what I'm talking-about, but in reality I just know what I've seen before. 

Car has 150k miles, no discernible driveability issues or fuel-economy issues. It does have some cold-starting issues. It does not stall, does not stutter, and is not losing any power that my butt dyno can feel... but the car has always been underpowered IMO. 
It's mostly a city-car, so fuel economy has always been pretty terrible and I have 10 years of self-calculated fuel stats to prove it! We bought it new. 

It originally started as a P0128 and P0171, along with a few other ones. One of which was a misfire code. 
The Secondary Air Readiness also refuses to Complete. 
All other Readiness monitors complete just-fine: O2 Sensors, MAF, etc. 
I suspect that all these codes are somehow related, because the car did not have any codes whatsoever, and these codes all happened at the same time. 

For the P0128, I diagnosed the P0128 to a low coolant. I refilled the coolant reservoir, cleared the codes, and that one has not returned. I'm curious where the coolant went, but I think this one may have been a coincidence? 
Without really diagnosing anything, I swapped in a new set of OEM-spec plugs, cleared the codes, and the misfire code has not returned. The plugs were the original factory plugs, so I figured it was time to swap them out anyway.
I didn't notice any abnormal burning or discoloration on the plugs. 
While I had the coils/plugs out, I checked cylinder compression - consistent across all 5 cylinders. 

The P0171 (only code remaining) and the cold-starting (and possibly oil leaks) have proven to be trickier... though I think they are somehow related. 

I cleaned the MAF and it made no difference - it still takes an extra 1.0 - 1.5 seconds of cranking before turning over on cold cranking. 
I unplugged the MAF and tried to start the car, and it has the same cold-start issue. 
So I don't think it's MAF related. 

Here's the weird part: 
The Freeze Data for the P0171 happens at 50mph and something like 2200 rpm, not at idle... otherwise I would suspect the O2 sensors. 
It looks like it's happening on a highway stretch and yet I cannot reproduce it at all. Car feels fine on the freeway. 
Freeze Data shows Long Term Fuel Trim is at 19%. Short Term Fuel Trim is at 0%. Weird, right? Maybe? I'm not sure I understand Fuel Trims completely... so maybe it's not weird? 
I do not have a way to measure the live data. 

I suspected a failing fuel pump or a failed Fuel Pressure Regulator, but I checked the fuel pressure (thanks AutoZone Loaner Program!) and it is at 0-10 psi when completely cold, primes up to 45-50ish psi once the ECU is on, and comes up to 55psi once the car starts up. 
No fuel pressure dips upon application of throttle, and (at least with no load) the fuel pressure maintains at 55psi up to 3000 rpm. 3k RPM is just where I stopped, I don't know if fuel pressure drops after 3k rpm, or if fuel pressure drops when there is more load. 
I am starting to think it's not Fuel related as I originally thought. 
The reason why I originally suspected Fuel-Delivery was that the cold-start issue goes away if the car is already warm. 
I haven't completely exonerated the fuel delivery system, but the fact that it is an inconsistent/intermittent P0171 at freeway speeds really makes me wonder about this theory. 
I'm also saving this one for last, because my wife's Beetle has a metal tank, and has an expensive in-tank pump which will be a pain to swap out! 

At this point, I'm leaning more towards vacuum leak as the cause of the P0171. 

I don't have a way to do a smoke test, but I suspect that the Vacuum Pump is leaking oil... I've been trying to diagnose a mysterious oil leak for the past few weeks as-well. 
I changed out the oil filter housing to a CTS housing (bottom front of the motor) and fixed the drips at the front of the engine. 
While I was in there, I looked at the vacuum pump and it looks like it might be the culprit for a 2nd oil leak, and (I'm hoping) vacuum leak? If this is true, I think it would also resolve the P0171? Yes? 

I will be ordering the Spulen kit here pretty shortly... 

What does The Vortex think?

Any feedback/thoughts/theories would be appreciated. 
Updates as I have them! Wish me luck!


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## billymade (Jan 29, 2008)

Your initial troubleshooting and investigation of things; is impressive and you have done some good work! Bravo!  Lets look at the trouble code; that seems to keep coming back. :banghead:

http://wiki.ross-tech.com/wiki/index.php/16555/P0171/000369

For the above code; you may, have a combination of issues, going on. @ 150k, I would strongly suggest replacing the fuel pump (if it is original); it is most likely weak, at this point and I have a feeling, under load it isn't up to spec, able to maintain needed fuel volume. I had a 2.0L Jetta I was working on; it had the same lean code and at highway speeds, the fuel pump wasn't up to snuff but it did pass, all the "normal" fuel pressure tests. 

Another additional possibility; are some issues, unique to the 2.5L engine. The PCV, is integrated into the valve cover and the inner diaphragm, is known, to tear and cause a large unmetered vacuum leak. You can try the Dorman repair kit or replace the whole valve cover; as VW integrated the pcv, into the design of the valve cover. More info here; 

https://www.newbeetle.org/forums/2-5-liter-gas/65633-re-2-5l-pcv-valve-failure-solutions-dorman.html

As for the air pump leaking; the USP Motorsports delete kit, is a option but installers, have noted, you have to modify and "notch" the engine cover, to get it to fit on the new beetle (the kit; seems to have hoses, designed for the Jetta/Golf). 

Another option; is the aftermarket seal kit, that just "reseal" the Pierburg pump and feedback, after install, has been good. That could be a solution; that is cheaper and would maintain, the look of your engine cover but the delete, seems to be a good permanent fix as well, from the feedback we have heard about. 

Read more here: (unfortunately, the attached images are not visible with the recent website upgrades/changes): 

https://www.newbeetle.org/forums/2-5-liter-gas/146585-vacuum-pump-oil-leak.html

So, you have your work cut out for you; I suspect a possible vacuum leak @ the pcv and a weak fuel pump. You might pop up the rear seat and remove the access plate, check the fuel pump and see it has the original vw/audi logo, which typically, indicates it is the original one. 

On the newbeetle site; we have had some long troubleshooting threads on a 2.5L, it ended up having a aftermarket junk fuel pump, made by Airtex and it caused allot of drivability issues. 

If you decide to replace the pump; I would strongly recommend, a oem pump, which typically is VDO but you might check Bosch as well, which tend to be less expensive. 

As for your inability; to read "live data" and pending codes, I would recommend upgrading your scan tool. On the cheap generic OBD II side of things; you could get a app and the ELM327 dongle, bluetooth for Android and Wifi for Apple devices. These are cheap and available on ebay or amazon. 

On the VW specific side of things; you might check out OBDEleven, which runs on Android or the industry standard VCDS by Ross Tech, which runs on a Windows based PC or tablet. 

So, do some research; check out your PCV and see if your fuel pump, is the original one. Then, give us some feedback and we can go from there! Thanks! :wave:


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## addicted2sp33d (Jun 5, 2009)

Thanks for the reply! 

What is really confusing to me is the Freeze Data showing 19% LTFT with 0% STFT at the moment the P0171 happened. 
What do you make of that? 

How is that even possible?  
At freeway speeds the ECU is thinking:

I've had to put in a sustained 19% LTFT for most of my journeys.
At the moment, at freeway speeds, everything is OK so I'm running STFT 0%
But HEY! Just for fun, I'm going to throw a Lean Code anyway! :screwy:


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## billymade (Jan 29, 2008)

This might be helpful; you might borrow a scan tool with live data capability and troubleshoot things, that way. You could also; check things, like the maf readings, as well. Most auto parts stores; will rent a scan tool for free. 

http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info

Meanwhile, checking and repairing thing like a leaking vacuum pump and possible blown pcv; would theoretically, affect fuel trims. You could have multiple problems; which cN make diagnosing the problem, even more confusing. Fix what you KnOW is bad and recheck fuel trims, after each repair is complete and note the changes

Did you inspect the currently installed fuel pump and see if it is a original vw part or aftermarket pump?


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## addicted2sp33d (Jun 5, 2009)

*Fixed One Thing... Now Something New!*

So I installed the Integrated Engineering Vacuum Pump Delete, and used off-the-shelf parts to tap into the N80 vacuum line to get my brake vacuum. I went with the IE plate because it was $20.00 cheaper than Spulen, and it had recessed bolts. In case it matters to anyone, their current plates also have the square IE logo on them, not the flower-thing that you see in some of the pictures. 

To access Vacuum Pump, I removed the Battery, Battery Tray, Intake Pipe, Airbox (top and bottom), and a vacuum line, and there was still a coolant hose that ran right in front of the top 1/3 of the vacuum pump. I decided to work around the coolant hose, since it had enough flex for me to get at the bolts, and I didn't want to pour coolant all over the engine bay or onto the Shift selector electronics. 

Removing the Vacuum Pump was a breeze after removing the little plastic insert inside the pump. There was also oil vapor inside the brake booster line, probably from the vacuum pump not sealing properly. 

While I had the right-half of the engine bay clear, I did some housekeeping and cleaned the throttle body also. 

Putting it all back together, I torqued the IE Vacuum Pump Delete Plate to 15 ft-lb, I think I saw that somewhere, but could not find a good reference. I really need to get my hands on a Factory Service Manual!

Billymade, do you have the torque specs for the 10mm bolts for the Multi-Function Transmission Range Switch? I've heard it called the Selector Switch? Basically the big thing that has an electrical connector on it. I torqued it down to 7-8 ft-lb, just to put everything back together, I really didn't want to strip anything. The selector/switch doesn't move, but the bolt still felt like it should be tighter.

Put everything back in place and spliced my vacuum source from the N80 line. The way I routed the hoses, I didn't have to cut into the engine cover at all, and you can't even see my splicing unless you take the cover off. It looks legit. :laugh:

In total, it probably took me 3-4 hours, mostly because I was also cleaning other things while I had a chance. I think if someone knew what they were doing, 2 hours would not be out of the question. 

I cleared the codes and went for a test drive. 

I'm happy to report, the car runs smoother and quieter, and definitely does not have the rattle anymore. I had always wondered what that rattle was, but it's been like that since Day 1 (we bought it new), so I figured it was supposed to sound like that. 
As far as I can tell, no more oil leak. 

Looking at the Vacuum pump and the cover plate, it definitely had a leak, I could see on the cover where the seal was broken, and there was metal-on-metal contact. 

End result, is the P0171 has not returned (not even Pending), but in its place I'm now getting a P0068 and P0101. 
LTFT and STFT are behaving normal now. Live data showed LTFT had a big initial jump to 10% at startup, but then trended back down towards 0%. 
STFT has some occasional jumps under load, but ultimately returns back to 0%. 

Hopefully the P0171 does not return. 

I plan to do a Throttle Body Alignment tomorrow, clear the codes, and go for another drive... see what happens. Fingers Crossed!


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## addicted2sp33d (Jun 5, 2009)

Early Morning, cleared the codes one more time, and ran the Throttle Body Alignment procedure. Car made a bunch of clicks/whiny noises, and was done. 

P0068 and P0101 have not returned, and so-far-so-good on the P0171... but then I was never able to produce the error on any of my test drives. 
Somehow my wife just has the evil magic touch on this one, so we'll see how she does this week. 

The Secondary Air Monitor still hasn't cleared, but it's only been a few hours... and all the other monitors have cleared. 

I think my next task will be to do the official VW Drive Cycle... see if that will get the Secondary Air Monitor to run/pass. 
Time is running out! Registration/Smog is due in the first week of August! I DO have a "Day Job" Monday through Friday.

The car doesn't have a rough idle, and I tested the PCV Valve by putting my finger under the little breather hole that Humble Mechanic talks about in this video: https://www.youtube.com/watch?v=E7wXBW28Tj8. 

No leaks, but I figured since I'm in a fixing-mood, I went ahead and ordered the replacement diaphragm from Dorman. I think I might also change out the fuel pump just because it's old - that's going to hurt though. 

It will easily be the most expensive part I've replaced in this entire adventure:

Bosch Spark Plugs (FR7HPP33+) were $55.00 including shipping. (1 hour of labor)
CTS Oil Filter Housing was $55.99 including Shipping. (1 hour of labor, did it with an oil/filter change)
The Integrated Engineering Vacuum Pump Delete Plate cost ~$59.99 bucks including shipping (I ordered a few other things with it). (4 hours of labor)
Hoses/Adapters/Hose Clamps/etc. cost $15.00.

Cheapest (New) OEM Fuel Pump that I found has been $200-$300+ range. (probably 1-2 hours of labor).


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## billymade (Jan 29, 2008)

Ok, so, it looks like the repairs; have addressed the issues, that we figured were causing the trouble codes. The readiness tests; will take a some time, to pass/fail. You have done excellent work here;  let us know, if any issues, come back, codes return and if all your readiness tests, end up passing! Hopefully, you are all set; for smog testing! eace: Thanks!


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## addicted2sp33d (Jun 5, 2009)

My wife's touch triumphed again. That pesky P0171 has returned. The P0068 and P0101 are gone. 

I am now going back and re-evaluating the things that I had previously thought were good: MAF, O2 Sensors, and Fuel Pump. 

I ordered a new MAF, along with a Foxwell NT201 Scanner. I want to see if the O2 Sensors are oscillating like they're supposed-to. I have OBD Eleven, but its "Live" data only shows instantaneous live data. It does not plot over time. 
Things that change over time at a quick frequency (like O2 Oscillation), don't move in OBD Eleven. For example, if I look at the O2 Voltage output on my OBD Eleven, it just shows 0.455 V with a few small movements at idle. It doesn't show the oscillation. 

On a more positive note, I received the Dorman PCV Diaphragm and installed it last night after work. 
It does not come with instructions, and I had to break the old cover to get it off the valve cover. I understand now why the Dorman diaphragm comes with its own cover! 
Someone with better mechanical skills might be able to pop all 6 of the little pins to slide the cover off in one piece. 
The OEM cover feels more substantial, and the Dorman diaphragm itself feels a little flimsy compared to the OEM diaphragm. 


Repair Expense Tracking:


$55.00 - Bosch FR7HPP33+ Spark Plugs + 1 Labor
$60.00 - CTS Oil Filter Housing + 0 Labor

$60.00 - Integrated Engineering Vacuum Pump Delete Plate + 4 Labor
$21.00 - Dorman PCV Diaphragm
$80.00 - Bosch 0280218071 MAF + 0 Labor
$15.00 - Hoses/Adapters/Hose Clamps/etc. 

I just tell myself that this car is 10 years old with 150k miles, and has been completely trouble-free until the A/C went out last year... so it's about time to change out some of these components anyway!


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## billymade (Jan 29, 2008)

Yes, after 10 years 100k miles; we typically see, a number of parts, reach “end of life” and need replacement. 10 years without any major problems; i think is pretty good actually, i’ve had much more problems with my earlier 2000/2002 new beetle 1.8T’s. Each vw has it’s unique issues but i got the feeling the later models, they worked out, many of the “bugs”, the older models had. The 2.5L; seemed like a pretty solid engine aside from early timing chain assembly failures and pcv’s eventually going bad. @ 150k, you might check the timing chain tensioner/buffers for wear and if the chain, is stretched out and loose. While, they do last longer then timing belts; they do eventually wear out, get noisy and need replaced. Keep in mind; a related catastrophic failure , would result in bent valves and a expensive repair bill. 

While you are waiting for parts; it might be a good time ti test your fuel pump and see if it is in spec, if it is the original pump @150k, it is probably due for a new one.

Fuel pressure testing: (2007 bpr engine code):

https://workshop-manuals.com/volksw...l_pressure/system_information/specifications/


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## addicted2sp33d (Jun 5, 2009)

I already tested the Fuel Pump: 

10-psi when stone-cold
45-ish psi once you turn the car on (without starting)
55 psi at idle

I think that's still within the normal operating range, and again that would be the most-expensive component, so I'm saving that for last. 
The Vacuum Pump was the most-difficult install, so the fuel pump will be a comparative breeze. 

The Freeze Data for this most recent-P0171 says the car was only moving at 33mph with something like 30% throttle, where the car shows 15% throttle even at idle... that's why I think this might now be a sensor issue, either MAF or O2, maybe a loose connection or an intermittently failing sensor? 

I assumed the MAF and O2 sensors were OK since they passed the OBD II diagnostics, but they COULD pass those tests and still provide inaccurate readings. We'll see how the new MAF works out... it arrives tomorrow. 

Once I get my new scanner (also arriving tomorrow), I'll be able to see if the O2 Sensors are oscillating like they're supposed-to. 


Who knows... I might end up changing out O2 Sensors and a Fuel Pump this weekend!


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## addicted2sp33d (Jun 5, 2009)

So something weird happened yesterday: the MIL light turned off on its own! 

Surprised, I decided to plug in my new toy (Foxwell NT201), and see WTF was happening. 
I plug it in, and SURPRISE SURPRISE! No Codes, No Pending Codes. 
I thought that is WEIRD... codes don't just go away on their own. 

Foxwell still has not earned my trust, so I bust out my old reliable Actron. 
Actron finds the P0171 is still there, with another Pending P0171... but for some reason the Foxwell just can't see them. 
I think the Foxwell only has 60 DTCs, while my Actron has 192. 

Also, the Foxwell can see live data, but for some reason it does not give me O2 Sensors as one of the available live-data options. It doesn't even offer live LTFT or STFT. 
Live Data options only include boring stuff like System Voltage, Throttle Position, and other things that were not important enough to remember. 

I even tried Foxwell's device update feature. No dice. 
Foxwell still sees no codes, though it DID see that the Secondary Air was still pending, but any $10.00 Readiness Tester device can tell you that these days. 

I decided to plug this Foxwell into my Mk7 Alltrack just to see if it was the tool or the Beetle CANBUS. 
Turns out it's about half and half. I did have more Live Data Options in the Mk7, but I still didn't have O2 Sensor Voltage. I DID gain LTFT and STFT. 
Either way, I think I'm going to return this Foxwell for the simple reason that it couldn't see codes that my 20 year-old Actron could see. Yay Amazon Prime! 

I swapped in the new MAF, cleared the codes, and went inside for dinner.


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## billymade (Jan 29, 2008)

Yes, I think the Foxwell; should be sent back. Foxwell, does make some VAG specific scan tools; that are probably more capable but their pricing is getting into the range of the better quality VW/Audi specific scan tools, like VCDS. If you are looking for a inexpensive way; to check live data, consider a ELM327 and a obd II app. Get a Wifi version for Apple devices and Bluetooth for Android; tablets or phones and even a windows pc, will work with the ELM327. While inexpensive; you would be surprised, at it's capability, when combined with a OBD II app on your phone or other mobile device. 

https://www.google.com/search?q=ELM...rome..69i57.6710j0j7&sourceid=chrome&ie=UTF-8

Since you have multiple Volkswagens in your life; you might check out OBDeleven, which has allot of features, that makes it easy to change various settings on later model VW/Audi cars and it is a similar wireless dongle type device but is only Android based at this time. 

https://www.google.com/search?ei=Hx...01...0i227i273k1j0i131i20i264k1.0.BnXK8Bya1bo

After that; VCDS by Ross Tech is a very mature product and runs on a Windows based PC, not a convenient as OBDeleven or the ELM327 but it really shines, in the support it provides by a USA based company, lifetime software updates, to keep it compatible with the latest VAG models and solid documentation, widespread use in the professional/diy VW repair industry. 

https://www.google.com/search?ei=bh...4k1j0i131i20i264k1j0i22i10i30k1.0.GYmbZMJXuNQ

Let us know; how the parts swap goes, how the car runs and if you get any codes, popping up again! eace:


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## petethepug (May 25, 2001)

Damn good info on the meat and potatoes involving the 2.5. I have to remove my air compressor and install the Spulen brake vacuum delete kit. I've also had no power assist on the brakes for over a year that I've been putting off. I've been really busy tipping the scales on things to do and creating other problems. This thread will get me over the hump to getting my 07 NB 3x White Vert back into ship shape. By pulling the driver/pass seats to clean and detail the leathers, get 10+ years of crap out from under them and pull the console to replace the Tip shifter guts I have to reset my air bags.

This is no big deal though because the steering wheel needs to be replaced and it appears as though the VCDS will allow me to recoup my investment quickly. Thank you so much for the info on how you dug into the vacuum delete kit. My underside is completely protected from rust and wear with a nice film of oil.

I needed the info and feedback on the VCDS Pro. I'll have to do a little research and see how cross compatible it is for the '02 allroad 6SP M and the Beetle. I'd love to get two birds with one stone.

I also have to invest in a "tech II" scanner for my '08 Denali XL AWD. I have 15K worth of service contract left on the truck and must have a diagnostic to ensure nothing gets missed that the contract will pay for on a vehicle that has over 125K clicks on the clock. Those service contracts are like kryptonite. I'm already $1K over in replacement parts and service in what I paid for the contracts. I fully intend to get my money's worth. Life is good because it just paid for the rear bagged suspension and its compressor installed by the GMC stealer. Thanks guys!!!


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## billymade (Jan 29, 2008)

VCDS by Ross Tech; is compatible with all VW’s and Audi’s from about 1996-on; I think it is a great value @ $200 with lifetime free software updates. 

http://www.ross-tech.com/vag-com/cars/applications/


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## addicted2sp33d (Jun 5, 2009)

Day 1 with new MAF... so far so good... but again, my wife has not driven it yet. 

Hoping we don't see a P0171 this weekend and we can smog the car on Monday!


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## billymade (Jan 29, 2008)

Cool! Good luck!


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## addicted2sp33d (Jun 5, 2009)

After a few days, P0171 is back! 

I have a new Bosch 1150 Scanner coming-in which should get here by Wednesday. 
Will this be the one to replace my trusty Actron 9175? 

Then I'll be able to see if the O2 Sensors are REALLY working. 
At this point, I still don't think it's the fuel pump. The car goes a few days without triggering a P0171, and if the fuel pump was failing I think it would be happening with more regularity. 

I may just order new O2 sensors and a Fuel Pump just for fun. At that point, I will have done a pretty complete 150k mile fuel/emissions service. Hahaha.

One thing I noticed, is that the P0171 freeze data always show that the car is in-motion and my wife says it always turns on after leaving our house. Sometimes she's on the freeway already (we live about 1 mile from the onramp). 
This makes me think it is happening once the O2 Sensors get warmed up and the ECU starts caring what the Sensors report. 

Smog deadline is looming... I may have to seek "Professional Help". Hahaha.


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## billymade (Jan 29, 2008)

Bummer! :banghead: Well, as always; it is BEST, to troubleshoot, using hard cold facts, that are a result of proper vw factory service manual testing procedures (verifiable data). Testing, the fuel pressure; would be a way, to rule that out as a problem. Most fuel pumps; get weak, after 10 years/100k and they just can't provide, the needed fuel volume, as needed, under load or when the pump gets hot. As noted; stick with high quality oem pumps, probably VDO is the oem for your car. Also, I believe, the fuel filter; has the fuel pressure regulator built into it, so that is another part, that could/should be replaced, as a regulator maintenance item. 

A number of cars I have worked on; have had a lean code and it ended up, being the fuel pump, even though, the fuel pressure seemed to have "normal" fuel pressure. On my 2002 1.8T New Beetle; the residual fuel press, after the car was turned off, went to zero (the check valve was bad). On, a 2001 2.0L Jetta; the fuel pressure at idle, was within spec but under load, the car ran horribly, had a hard time starting when hot but when cooled down, started ok. In that case; the lean code, seemed to kick on, on highway speeds and high volume/load scenarios. The fuel pump; was bit hard to diagnose but running issues, kept getting worse, worse, as time went on and while, typical testing procedures, didn't indicate a bad pump, a new one, fixed the problem!  So, I think; you can do the best you can with testing procedures and resources you have, then make a decision, as to what changes to make. After installing new parts; take a test drive and retest; to confirm, the problem is fixed, that is the best you can do, aside from taking it to a pro shop. Although, at this point with many shops; being over $100 an hour, replacing some questionable parts, is probably still cheaper, then having them fix it. At the end of the day; you have to decide what to do, I think, you have narrowed things down, to a couple of things on the list! eace:

http://wiki.ross-tech.com/wiki/index.php/16555/P0171/000369

_Note: the list of possible issues; I would work my way down the list and hopefully, you will find the problem, through a process of elimination! _

*16555/P0171/000369 - Fuel Trim; Bank 1: System Too Lean

Possible Causes

Mass Air Flow Sensor (G70) defective
Intake System Leak(s)
Possible Solutions
Check Mass Air Flow Sensor (G70)
Check Fuel Pressure Regulation
Check Fuel Pump
Check Injectors
Check Intake System for Leaks
Check Exhaust System for Leaks
Check Secondary Air System for Leaks
Check Vacuum Pipes for Leaks*

_You have been doing great so far; I hope, you find the culprit and can pass your smog test! Good Luck! _


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## addicted2sp33d (Jun 5, 2009)

So I got my new Bosch Scanner and it can definitely replace my Actron 9175. It recognizes more PIDs (329) than my Actron (192). 
I think I might be putting my Actron on eBay or Craigslist in the near future. 

But you're not here to read about my toys, you're here to see what is happening with that P0171! 

I hooked up my fancy-new scanner to look at the Pre-Cat O2 Voltage, and it does indeed oscillate like it's supposed-to... for a little bit. 
Then it just plateaus at about 0.7V - 0.8V and stays there... at least at Idle. I didn't do a drive test yet. 

It starts oscillating again upon application of throttle, but again, it only oscillates for a little bit and then it plateaus again... with the car on the driveway, no driving. It was late and I was wearing pajamas. 

I'm still undecided if that's normal or not... I don't think-so. I will do a drive test after I get home tonight... see what it looks-like. 
Everything that I've seen online says it should always oscillate, even at idle. 

I think that 0.7V plateau (O2 is reporting Rich Condition) tricks the ECU into thinking it's putting too much fuel in. 
ECU dials-back the fuel, in reality, creating its own lean condition.
Then in a "moment of clarity" when it's actually oscillating properly, the O2 sensor catches the lean condition and records the P0171. 
This theory would explain the intermittent nature of this particular P0171: It doesn't turn on right away, doesn't happen at idle, and does not happen all the time.


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## billymade (Jan 29, 2008)

No worries; about discussing scan tools, they have become, crucial in troubleshooting modern cars. I use VCDS, and a cheap ELM327 with a my iPhone with a obd II app. 

As for the 02 sensor; I have heard of "tired" sensors, that, as they get old, cannot or do not, respond as quickly as they used to or get stuck, at a certain reading/setting. Do you have any idea; how old, the 02 sensors are? If you decide to replace them; stick with oem Bosch. You can get them pretty cheap online or use the various discount codes, many local auto parts stores, post on their websites (e.g.: pep boys, autozone, oreilly's, advance auto, etc). Most will allow you to purchase them online with the discount codes and go pick up the parts, at the store. I got a coupon code at Pep Boys and purchased it online; picked it up at the store, I got a genuine Bosch 02 sensor, for less then $50. My car ran better; the sensor, seemed to react quicker and I have better gas milage. I think, 02 sensors; are becoming close to, "tune up parts" and should be replaced, a certain interval, to keep our cars running at their best tune levels. I found the install; to not be too hard and it was definitely, worth it and inexpensive, definitely, made a difference. 

You can look up the correct Bosch part number; for your car here:

https://www.boschautoparts.com/en/ 

Let us know; what you do next and decide, what to do, any results from changes you make. Thanks! 

PS: in discussing 02 sensors; keep in mind, they are "reacting" to issues, upstream from them. SO, testing your fuel delievery; like, fuel pressure and the fuel pump, should not be ignored.


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## addicted2sp33d (Jun 5, 2009)

*O2 Sensor is Being Weird...*

Did a drive test after work yesterday and was able to reproduce the linear O2 Voltage signal pretty consistently. 
The O2 Voltage would start at 0.455V, then oscillate for a few seconds, then it would flatten out at ~0.7 Volts. 
While pulling away from a stoplight, the O2 Voltage would start oscillating again, but then return to a plateau at ~0.7V. 
I don't think this is normal O2 behavior, so I will swap out the O2 Sensor this weekend. 


The strange thing is the LTFT reads +18%, while the O2 is reading a persistent 0.7 Volts. 
The ECU thinks there's not enough fuel, while the O2 Sensor is reporting that there's too much fuel. 

Shouldn't the ECU bring the fuel trims down if the O2 is reporting a rich condition? Is the ECU just ignoring the O2 Sensor, even in Closed Loop operation?
But then where does the P0171 come from? How is a lean condition possible with the ECU dumping so much extra fuel and the o2 Sensor reporting a rich mixture? 

If the ECU thinks the engine/O2 are "cold", then it would ignore the O2, but then why would it go into Closed Loop if it thought the engine was still cold? 
Maybe a stuck thermostat? I checked the coolant temp, and it was consistently in the 190F - 200F range. Nothing really out of the ordinary there. 


Any other theories Vortex Geniuses?


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## billymade (Jan 29, 2008)

I always; read over the ross tech page on fuel trims, to think over things, when evaluating my fuel trim readings. 

http://wiki.ross-tech.com/wiki/inde...ifferences you see with any changes you make.


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## addicted2sp33d (Jun 5, 2009)

*Awwwww Yeah...*

So I ordered and installed three things this past weekend: 

1. Fuel PumpContinental VDO 2910000105100 Fuel Pump (OEM Manufacturer for VW/Audi).​VW/Audi Part Number 1J0919051N for Mk4's with a Metal Fuel Tank. 
The VW/Audi branded one was $500+.
The OEM pump I pulled from the car does not have a VDO part number, but it has "VDO" stamped on the fuel-level sender. 
https://www.fcpeuro.com/products/volkswagen-fuel-pump-assembly-vdo-1j0919051n 

From what I can tell, the "metal fuel tank" thing applies to CA and HI cars. I'm guessing Beetles in other states have different pumps. 
I originally ordered this one because it was still BOSCH and was MUCH cheaper, not knowing there was difference, and of course it did not fit:
https://www.amazon.com/Bosch-69740-Original-Equipment-Replacement/dp/B001C602HW​

2. Bosch 17024 O2 Sensor:My O2 Sensor was not oscillating like it is supposed-to, and would get "pegged" at 0.7V, basically reporting a rich condition all the time.
https://www.amazon.com/gp/product/B0028MN546​

3. Valve Cover Gasket:I noticed an oil leak from the valve cover gasket on the passenger side of the valve cover.
https://www.amazon.com/gp/product/B004983ESE​


I waited until the fuel level was lower in the tank, as I didn't want to work in a gasoline swimming pool. 
Saturday night, the Fuel light came on, and I knew it was time. 

This morning, I parked the car with the passenger-side wheels on the sidewalk, creating a notable slant to the car. All the remaining fuel sloshed over to the driver's side, which made the fuel pump area a little bit dryer. The fuel pump is under the rear cushion, on the passenger side of the car. I took the rear seat cushion out completely, which greatly improves the workspace. 

Considering the tight quarters in the tank, the job was remarkably easy.
For removing the fuel pump itself, I found that it REALLY helps if you unlock the fuel pump from the in-tank cam-base, and lay the pump on its side inside the tank. Don't worry about "shorting" any of the electronics. This pump is normally submerged in fuel, so you're not exposing it to anything it hasn't seen before. 
Everything is done "by feel" as the hole is only big enough to put your hand in OR look inside the tank... but never both. 

This video series helped me a lot: 
Video 1: https://www.youtube.com/watch?v=hvLs31Zw-zo
Video 2: https://www.youtube.com/watch?v=A-mOX9_PZJg
Video 3: https://www.youtube.com/watch?v=a0lE03lI6T8
It's not mentioned in the videos, but I found that laying the pump on its side will give you more room (and slack in the hoses) to maneuver and disconnect all the hoses. 

The Fuel pump itself only took me about 15-minutes to remove and swap out. Not difficult at all.
The only thing to be careful-of is to surround the tank with disposable towels and not let the fuel hit the carpets. There WILL be fuel spillage. 

Be careful as you lift the pump out of the tank... this pump will retain about 3-4 cups of fuel INSIDE the pump, so it will constantly drip. I noticed a hole at the top, so I flipped the pump upside down and poured the fuel back into the tank. 

Other than managing the spillage, the removal/install was remarkably easy. The Vacuum Pump removal/install was WAAAY more work. 

O2 Sensor is pretty straightforward. I rented the O2 tool from Autozone, and swapped in the new sensor. 

Valve Cover was also very easy, just a lot of bolts. 
I did notice the Fel-Pro gasket that I purchased was about 1-2 mil thicker than the OEM gasket that I pulled out. Not sure if the OEM gasket compressed with age, but the new Fel-Pro definitely created a tighter seal than the old gasket. 
Hand-start all the bolts to make sure everything is properly threaded.
Then hand-tighten all the bolts with just the socket and an extension (no ratchet driver). 
Then torque down to 10 NEWTON METERS. This works out to be 7.5 ft-lb! 

The whole job took about 2 hours including a quick neighborhood test drive just to make sure everything was working. 

After getting everything back together, went for a longer test drive, and so-far-so-good. 

I don't know which part actually fixed the problem, but the O2 Sensor now oscillates like it's supposed to, and the LTFT now reads about 3%. I did a few Ricer Full-Throttle pulls onto the freeway, and kept an eye on the O2 Voltage, STFT, and LTFT... all looked normal. 

The Integrated Engineering Vacuum Delete Plate is still holding, with no oil spray. 
My Brake Vacuum re-route is still holding.

All the Emissions Monitors have cleared (except the Secondary Air)... but I can pass with one incomplete Monitor. 
The key is that the P0171 has not returned, and I don't even see any pending P0171 codes.

Here's my final tally of parts: 


$359.00 - VDO 2910000105100 Fuel Pump Assembly + 30 Minutes Labor
$15.24 - Fel-Pro VS 50735 R Valve Cover Gasket + 30 Minutes Labor
$89.78 - Bosch 17024 O2 Sensor + 30 Minutes Labor
$55.00 - Bosch FR7HPP33+ Spark Plugs + 1 Labor
$60.00 - CTS Oil Filter Housing + 0 Labor (Oil Change)

$60.00 - Integrated Engineering Vacuum Pump Delete Plate + 4 Labor
$21.00 - Dorman PCV Diaphragm + 30 Minutes Labor
$80.00 - Bosch 0280218071 MAF + 30 Minutes Labor
$15.00 - Hoses/Adapters/Hose Clamps/etc.
​
Total Parts: $755.02
Total Labor: 8 Hours

How much of it was really necessary? Who knows. 
I'm estimating this would have been about $1600-2000 to do all the same work, but I also think I've upgraded the car with the new CTS Oil filter and IE Vacuum Pump Delete. 
This is the first major issue that we've had this with this car... and even then, if it wasn't for California Emissions, the car otherwise drive's perfectly fine. I probably would have stuck with the current setup until something legitimately failed. 

I have previously worked on P0171 on my S14 and my wife's EK Civic (the car she had before the Beetle), and both were easily resolved with new O2 sensors. 
Maybe I should have started there? But what fun would that have been? 

Time to go ace the Smog Test!


If anyone has any questions, feel free to PM me.


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## billymade (Jan 29, 2008)

Excellent work; I’m glad your problems, have been resolved.


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