# P0170 Code



## rad1026 (May 5, 2016)

New here but I have been lurking for a little while. I will go introduce myself as soon as the moderators approve me. I haven't owned a VW since my 1992 Jetta, which was a great car. Just purchased a pretty yellow 2001 Beetle 1.8T. It has 132,000 miles and just had a dealer service timing belt and water pump less then 5,000 miles ago. The car drives great but on the way from Denver to Albuquerque it threw a P0170 code. I initially thought it was just because we had to drive about 10 miles on a washboard dirt road and thought I possibly jostled an o2 sensor or something. I cleared the code but after about two weeks of driving it has come back. I did a bunch of reading and started by looking for vacuum leaks. I found the hose from the diverter valve to the charge tube behind the engine to have a long tear in it. I have it on order, I hope I ordered the correct part, Pressure control line 1C0145712E.

This weekend I will probably pressurize the system and see if I can find any more leaks. In the mean time I have hooked up my OBD software and have a couple readings that I don't like.
I'm only getting between 2.0 and 2.3 off the MAF at idle and from what I have read it should be between 3-5. Also I am getting 0 volts from the number 1 O2 sensor. Could that pressure control line cause the low MAF reading? Will that affect the O2 sensor reading or should I just plan on replacing the O2 sensor. Maybe the wire connection came lose from the O2 sensor on that washboard road, guess I should check that first.

Anyway, happy to be another VW owner. Love the little beetle. Thanks in advance for any help.


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## billymade (Jan 29, 2008)

What scan tool; are you using? What engine is in your car? I am assuming you have a 1.8T. 

http://www.obd-codes.com/p0170

Sounds like you are on the right track; I would retest things, after your replace that boost hose. A massive vacuum leak; should be repaired, before trying to evaluate readings. The above link; discusses the maf and 02 sensor, being a possibility. As noted; live data and testing is the best way to see what is going on (for the MAF: idle and @ WOT). 

https://www.google.com/search?q=vcd...ome.0.69i59.4416j0j7&sourceid=chrome&ie=UTF-8

Another good indicator of your tune status; is your fuel trim levels, which can give you direction as well: 

https://www.google.com/search?q=vcd...7&sourceid=chrome&ie=UTF-8#q=vcds+trim+levels

Replace the boost hose; repair any vacuum leaks and test your maf, fuel trims and we can go from there. Thanks.


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## rad1026 (May 5, 2016)

I am using ODBCOM software with a USB connection to my laptop. I have had the software for several years. It is reading 16 sensors on the VW including O2 voltages, MAF, fuel trim levels, RPM, throttle position sensor, coolant temp, and some others I can't remember off the top of my head. So that hose, what they call a pressure control line is a boost hose? 

Thanks for the reply. I will get back when I have replaced the hose.


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## rad1026 (May 5, 2016)

okay, had a chance to install the new Pressure Control line hose yesterday. The old one had a 2" long gash in it. I hooked the computer back up and started the car. I noticed the idle was rough and then smooth and rough and then smooth. The Short Term fuel trim was going negative then positive then negative and positive. Hopefully that is an indication it is trying to correct for the long term values. My MAF reading started out at 6 then as the coolant temp increased gradually settled in at its previous readings of around 2.7. So I took the car for a run and did the WOT test to see what readings the MAF gave me. The MAF seems like it is functioning properly WOT readings were over 100. I am still not getting any voltage off the pre-cat O2 sensor. I guess my next step is to replace that unit. I still want to pressurize the system and see if I have any more leaks. I just ran out of time this weekend. I also want to check my fuel pressure. I haven't cleared the P0170 code yet, but I'm thinking it is being cause from the O2 sensor. 

I have a couple questions:
Where do I check the fuel pressure?
Are the two O2 sensors the same? 

Thanks for the help


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## billymade (Jan 29, 2008)

Well, as suspected; it sounds like the boost leak, was causing other things like your Maf to go goofy. From what you're saying; your MAF #'s seem to have stabilized, you might get some MAF cleaner and spray it, just for the heck of it and see if your idle #'s improve a bit. 

CRC 05110 Mass Air Flow Sensor Cleaner - 11 Wt Oz.

https://www.google.com/search?q=MAF...05110+Mass+Air+Flow+Sensor+Cleaner+-+11+Wt+Oz.

Also, you could get some contact cleaner, to spray on the plug and maf sensor, to assure the contacts are good. I also, put some ignition dialectic grease; on mine, to improve the connection. 

CRC 5103 Quick Dry Electronic Cleaner - 11 Wt Oz.

https://www.google.com/search?q=crc...+5103+Quick+Dry+Electronic+Cleaner+-+11+Wt+Oz.

Permatex/Dielectric tune-up grease
Part Number: 22058

https://www.google.com/search?q=per...8#q=Permatex/Dielectric+tune-up+grease++22058

As for fuel pressure testing; you put the tester inline of the fuel hose, before the fuel rail. Here is the factory fuel pressure testing info: 

http://workshop-manuals.com/volkswa...essure_vacuum_and_temperature_specifications/

http://workshop-manuals.com/volkswa...nosis/with_manufacturers_scan_tool/page_1781/

I used a basic fuel pressure tester; the one I had was from Harbor Freight but you could probably rent one, from your local auto parts store. 

https://www.google.com/search?q=fue...69i57j69i60.4142j0j7&sourceid=chrome&ie=UTF-8

The 02 sensors; are not the same, I recommend oem Bosch and get the "oe" version, not the "universal", that way they will be exactly the same as the originals. You can look up the correct part numbers; on their website: (amazon.com; tends to have the best prices): 

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


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## rad1026 (May 5, 2016)

thanks for the help. I just noticed you are not too far from me down in Las Cruces. I go down to the Butte all the time. 

I will order up a O2 sensor and see how that effects things.


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## billymade (Jan 29, 2008)

Hey, it is a small world, huh?!? :wave: 

A fuel pressure test, checking fuel trims; are a good idea.

As for the B1S1; 02 sensor, being totally dead, that is not good! Here are the service manual pages; for testing the 02 sensor and checking the wiring harness. 

http://workshop-manuals.com/volkswa...r_regulation_after_converter_check/page_3997/


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## rad1026 (May 5, 2016)

Ha! Fuse, guess I should check the fuse before I go any further. Thanks for the diagnostic info.


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## rad1026 (May 5, 2016)

All fuses are good. I went ahead and replaced the wide band O2 sensor last night. I think I wasted $50. The new sensor still shows no voltage. It does however produce a lambda reading, how could that be? I am going to have to email the OBD software company and ask about that. I started up the car after installing the O2 sensor and immediately threw two more codes, P0300 and P0302. Random misfire probably on #2 cylinder. Really? Great..... My MAF sensor idle reading still seems really low, around 2 g/m. Guess I still have some work to do. And I cleared the codes, but I can't get the check engine light to go off. What?


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## billymade (Jan 29, 2008)

What brand and part #; was the new sensor? I had a problem; where I replaced my 02 sensor and the CEL came back on, along with a trouble (02 sensor heater) code. I went ahead and did a hard reset; remove the pos/neg cables, touched them together for a moment and reinstall. This resolved the light and the code. 

As for not "seeing" the 02 sensor; some scanners, I have heard are not able to read it. 

http://wiki.ross-tech.com/wiki/index.php/16684/P0300/000768

http://wiki.ross-tech.com/wiki/index.php/16686/P0302/000770

Check out this thread; for some ideas, about diagnosing the misfires. 

http://forums.vwvortex.com/showthread.php?7881986-2001-NB-1-8T-Runs-Rough


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## rad1026 (May 5, 2016)

I received an email from the OBDCOM software company, "Getting just the lambda reading is normal in the software and of course indicates the sensor is functioning."

So now I know I should have been looking at the lambda reading on the wide band O2 to begin with and not the voltage. 

I'm going to check for DTC codes again tonight and see if anything came up from my wife's drive today and if not I will disregard the new p0300 and 302 for now and just try a re-boot. I will continue to look for vacuum leaks, but the low MAF sensor readings are still concerning me.


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## billymade (Jan 29, 2008)

Now, that you fixed the boost leak; I would recheck ALL your readings, paying particular attention to fuel trims (more than +/- 10 % should be investigated), mafs readings, etc. I would buy a can of maf cleaner and clean your maf, just for the heck of it; see if that improves your readings. Post up that info and we can go from there, thanks. eace:

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


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## rad1026 (May 5, 2016)

I did another test last night ST and LT fuel trims at idle and then at 2000 rpm. After the car is warm and at idle my LT is -14.8% and ST between 3.1-6.3%. At 2000 RPM LT remains at -14.8% and ST between 10.9-15.1%. Huge swings. The LT obviously indicates the PCM is reading a rich condition and trying to compensate with leaning out the trim. But the ST at 2000 going up so high is throwing me. A vacuum leak would cause the ST to immediately lower and the LT to follow suit just more slowly. Am I getting confused? Either way these swings could certainly be caused by faulty readings from the MAF sensor.


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## rad1026 (May 5, 2016)

Last night I cleaned the MAF sensor, disconnected the battery and cleared the codes. After I did that I started the car and hooked up the OBD software. I wanted to clear out the LT fuel trim information and start over. Who knows how long the car had been running with that hose torn and it could have taken a long time to even out the long term numbers. I did get the MAF readings to come up a little to between 2.25 and 2.5. The ST fuel trim seemed to come down especially in the 2000 RPM range. I'm keeping my fingers crossed. My wife is driving it today and we will see if it throws any codes. I will hook it up again tonight and see what the LT fuel trim looks like.


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## billymade (Jan 29, 2008)

Cool, let us know; how the reset readings turn out, after all the readiness codes are set to "on" again.

https://www.google.com/search?rlz=1...QvwUIFygA#hl=en-US&q=vw+readiness+drive+cycle


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## rad1026 (May 5, 2016)

well I'm back. Took about a week and the P0170 code showed up again. I again went searching for any vacuum leaks and still have not located anything. I thought maybe the MAF sensor cleaning wasn't enough and I went ahead and replaced the MAF sensor with a BOSCH part. Cleared the code again and it took about two weeks to come back. I'm frustrated now. Also in the last few weeks my son has been driving the car. He says it has stalled on him now twice. Once on the freeway just driving along and it just died and once again not too far from his house. The second time he says he was running the air conditioning with the outside temp at about 101 degrees and it sputtered slightly before it stalled. The first time he said it started right back up and he was on his way. The second time he said he had to wait about 20 minutes before he could get it started again. 

I know my jeep has done that when I'm 4 wheeling in some hot temps. They call it "heat soak". It gets so hot under the hood the injectors act like the old carburetor vapor lock. 

I'm going to pull codes again hopefully tonight and see if anything else has come up. 

Any ideas?


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## billymade (Jan 29, 2008)

Scan and post the codes; we can go from there. My first thought; would be failing crank sensor, ignition or a fuel delivery issue. Smoke testing; is supposed, to be one of the most effective ways to find vacuum leaks.

http://www.obd-codes.com/p0170


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## rad1026 (May 5, 2016)

I was thinking crank sensor also, although the Cam sensor went out on my jeep and that gave the same issue. I replaced that several years ago and have never had that problem again. I will scan tonight and see if there are any new codes.


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## rad1026 (May 5, 2016)

finally had a chance to scan the code last night and the only code that came up was once again the P0170. The Short Term Fuel Trim was hovering between -1.6 and 1.6, so it seems like it is trying to get things in line. The Long Term was right at 3.1% which is a lot different from my initial readings a few weeks ago of -14. I looked for about an hour with a good flashlight and my glasses on and I still don't see any hoses that might be leaking. I think I'm going to have to try the smoke method or something. I really don't want to have to take this in to have someone look at it.


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## billymade (Jan 29, 2008)

You fuel trims levels; look a lot better, Ross Tech says under + or - 10% is acceptable or "normal". Watch the video; for more info: 

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

Are all your readiness set; to pass? 

http://www.ross-tech.com/vcds/tour/readiness.html

Did you check your maf readings; are they in spec at idle and WOT?

https://www.google.com/search?q=maf...ourceid=chrome&ie=UTF-8#q=+ross+tech+maf+test

Have you ever; checked your fuel pressure?

While, this may not be the primary issue; I have noticed, a dirty throttle body can cause more air to enter the system and cause some problems. A throttle body cleaning and alignment; couldn't hurt, especially, if it hasn't been done in a long time. Its amazing, how butter smooth a 1.8T; will idle, after a fresh clean (don't forget to clean the iat sensor as well; located right after the TB). I use the CRC 05078 Throttle Body and Air-Intake Cleaner - 12 Wt Oz. with excellent results.


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## rad1026 (May 5, 2016)

I don't have the VCDS software so I am not sure about the readiness. I know the software I have goes through a series of tests when it is communicating with the vehicle. I will have to pay more attention to what those tests are. 

I have not gone back through the MAF sensor readings. I really need to do a wide open throttle test and see how that reads.

I have not checked fuel pressure but I have a gauge and will do that and report back.
I will also clean the throttle body and iat and see how that goes. Thanks for the help!


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## billymade (Jan 29, 2008)

Cool, let us know; how it goes! :wave:


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## rad1026 (May 5, 2016)

I cleaned the throttle body and iat sensor last night. The throttle body was pretty dirty. Not saying it has never been done, but for sure it has been a while. It did make a difference in the idle. Not sure what aligning the TB means.


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## billymade (Jan 29, 2008)

Basically, it is the ecu; resetting, the parameters of the throttle body angles. If you don't have a vw scan tool; some say a "poor mans alignment", is turning the ignition to the "on" position and leaving it there for a couple of minutes, until the throttle body stops making noises. This has been debated ad nauseum, over the years but that is seen as one way to do it, if you do not have a vw specific scan tool. 

https://www.google.com/search?q=thr...ome..69i57.11289j0j7&sourceid=chrome&ie=UTF-8


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