# Dreaded P0240



## Slaghammer (Feb 8, 2016)

Hey everyone.

I know there are multiple threads out there for this issue, but I have not found a solution that has helped... For those of you that also patrol other forums, this will look familiar. I am at my wits end and am in need of help and hoping someone here might have a solution I haven't tried...

I don't mean to create a dead thread, but here is the story with hopes someone will have additional insight.

I bought a 2005 New Beetle with the 2.0L and manual transmission with a known emissions CEL.
I have replaced: the thermostat, the Cat x2, the O2 sensors.
I have a VAG-COM and can see what codes it is throwing (P0420) and its readiness. 
I have done the SeaFoam trick. 
It has a new air filter.
I have cleaned the MAF sensor.
I have tried new plugs (E3 diamond fire).

What else can I try or do? I would like to get this car on the road so it can start earning its keep!

Again, my apologies for dredging up another dead-end thread; I didn't want to hi-jack someone else's... 

HELP!!!


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## billymade (Jan 29, 2008)

P0240 Catalyst System Efficiency Below Threshold (bank1)

Well, you need to use VCDS; to figure out what is going on. You might start with fuel trims and then other tests (e.g. catalyst aging test, 02 sensors, etc.): 

http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info (+ or - 10% would indicate a problem; requiring more research)

http://forums.vwvortex.com/showthread.php?1265064 

Also, I do not recommend the spark plugs that you installed; many online, have noted them causing problems for people, that use them. I would stick with oem NGK plugs; go to the NGK website, to find the correct part number and install those: 

https://www.ngksparkplugs.com/

If this type of troubleshooting and testing is beyond your abilities or desire to do so, find professional help. One shop in your area; that advertises here is bluewater performance. You might give them a try and see if they can help: 

http://www.bwperformance.com/


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## PoorMansDub (Nov 28, 2010)

When you did the seafoam test did you notice any smoke coming out from any mating surfaces of the header? Sometimes p0420 is caused by a leak in the exhaust system that lets air in and messes up the O2 readings. 

I will tell you a secret that has worked for me over the years...buy an O2 spacer off eBay and install it on the rear O2. This will turn off the code and allow you to get it registered.


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## Slaghammer (Feb 8, 2016)

*More efforts*

Billyman

So I have replaced the spark plugs just to be safe. The long term fuel trim is sitting at 13.5% right now. Is there a test or series of tests to run to check the MAF? I have cleaned the MAF previously, but, it might be time for replacement. All of my readiness codes are clear as well. Additional thoughts?

Poormansdub

I have looked at the spark-plug anti-foulers, but there isn't enough meat left to allow the threads to bite. I will look on ebay.


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## billymade (Jan 29, 2008)

Did you run these tests and see what the results were? 

http://forums.vwvortex.com/showthread.php?1265064

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

http://www.ross-tech.net/vag-com/advertising/DiagnosingA_MAF_TechTip.pdf

Service manual testing procedures: 

http://workshop-manuals.com/volkswa...sor/component_information/diagrams/page_4919/


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## Slaghammer (Feb 8, 2016)

*Thanks*

Poormansdub, I forgot to mention that when I did the Seafoam test, I did not see much of any smoke from the exhaust...

Billymade,

Thanks for the info! I will look into the tests this week. I did do the Group 032 test from the Ross-tech wiki. That was were I got the 13% + in the second field (multiplicative). I appreciate the links! I feel like there is a lot more that the VCDS can do that I am just scratching the surface of... Any tips on a troubleshoot guide with the VCDS? Thanks in advance,

-hammer


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## billymade (Jan 29, 2008)

Maybe download the manual and look over the site, the ross tech wiki has trouble code definitions and other great info! You should also join the Ross tech support forums; they are responsive and helpful on there with questions, you might have.

http://www.ross-tech.com/vcds/download/current.php


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## Slaghammer (Feb 8, 2016)

Billymade,

Below is the results of the tests:
Block 002 - Load Registration - 2.25 g/s
Block 030 - Oxygen Sensor Regulation - 0111 most of the time
Block 032 - Oxygen Sensor Control Learned Values - 12.7%
Block 033 - Pre-Cat Oxygen Sensor Control - flucuates as indicated.

Block 036 - Post-Cat Oxygen Sensor Control - Test off (I could not get it to acutate for a 2.0L BEV engine.)
Block 034 - Aging of Pre-Cat Oxygen Sensor - Test off (I could not get it to acutate for a 2.0L BEV engine.)
Block 046 - Catalytic Converter - Test off (I could not get it to acutate for a 2.0L BEV engine.)

I'm still leaning to the MAF, but have not been able to find a reliable test, other than the idle test.


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## billymade (Jan 29, 2008)

This thread; has some good info, about testing the maf with VCDS @ WOT: 

http://newbeetle.org/forums/2-0-liter-gas/59939-definitive-aeg-maf-test.html


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## blksabbath (Jun 28, 2001)

Pull the trigger and buy a new MAF.


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## Slaghammer (Feb 8, 2016)

OK... so the old MAF had a Multiplicative vaule of 13% (across all RPM's). I replaced it and now the value is 3%. I reset the codes and the CEL didn't come back on for a while. But, all good things must come to an end, and so, the P0420 is back. What next? I haven't been able to find a O2 spacer that has a big enough port to allow the Bosch sensors to fit through and still have enough meat for the threads. :banghead: Any suggestions? 

On a different note, around a 1/4 of a tank of gas, the car will randomly cut out cruzing down the highway. It will only do it once and is like someone unhooked the coil. I have not been able to force it to happen twice. And potentially as unrelated, the battery drained this past weekend and when my wife tried to start it, the gas cap light was on. For the $8 for a new cap, I will test that out tonight. Any other suggestions would be greatly appreciated.


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## billymade (Jan 29, 2008)

You said; you replaced the MAF sensor, what brand did you replace it with? It is CRUCIAL that you replace it with the correct oem Bosch part; as aftermarket versions, can underperform or prematurely fail. You can look up the correct part for your car here: https://www.boschautoparts.com/en/

Since you have VCDS; you might try the catalyst aging, 02 sensor tests and see what the results are. 

http://forums.vwvortex.com/showthread.php?1265064

As for the "cutting out" with a low tank; have you ever done a fuel pressure test and see if the psi is in spec? Many of these older New Beetles; have weak fuel pumps and this can cause all kinds of problems. 

fuel pressure testing procedures: 

http://workshop-manuals.com/volkswa...l_pressure/system_information/specifications/

Bad and cracked coil packs; are a common problem for misfires as well. 

http://forums.vwvortex.com/showthre...eshooting-Coil-pack-on-2-0-AZG-AVH-BEV-or-BBW

So, as you currently stand; are you getting any new trouble codes, aside from the P0420? 

http://wiki.ross-tech.com/wiki/index.php/16804/P0420/001056


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## Slaghammer (Feb 8, 2016)

Hey Billymade,

I have replaced the MAF with the correct Bosch Part Number: 0280218060. Same with the O2 sensors. 

I have not thought to test the catalyst aging as it is only a month old, however it is an aftermarket (the second one I've tried, actually). I have not been able to find an O2 spacer that will fit the sensor.

There is one other code that comes up: P1539 - 35-00 - Clutch Pedal Switch Implausible Signal. Other than that, the VCDS shows a clean bill of health. I replaced the gas cap last night since the cap light came on when I had to jump it. I am assuming that this was more of a low voltage issue, but $8 is cheap insurance. I cannot think of what else it may be... What are your thoughts? There is a part of me that says to put the original Cat back in to see if that has an effect... It feels like I am close to the solution, but am missing the spark of a solution.

-Slag


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## Slaghammer (Feb 8, 2016)

This is the freeze frame data that is throwing the code:

Freeze Frame Data for address 10
PID02 DTC that caused freeze frame data storage: P0420 
PID03 Fuel system 1/2 status: Closed loop, using O2 sensors
... Engine off 
PID04 Calculated load value: 36.9 % 
PID05 Engine coolant temperature: 84 °C 
PID06 Short Term Trim - Bank 1: 0.0 % 
PID07 Long Term Trim - Bank 1: 1.6 % 
PID12 Engine RPM: 2750 /min 
PID13 Vehicle speed: 51 km/h 
PID14 Ignition timing advance for cyl #1: 28.5 Degrees 
PID15 Intake air temperature: 3 °C 
PID16 Mass Air Flow: 15.86 g/s 
PID17 Throttle position sensor: 20.0 % 
PID18 Secondary Air Status: Atmosphere/off 

Thoughts?


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## billymade (Jan 29, 2008)

I'm certainly no expert; the only things, that jumped out at me were the coolant and intake temps seemed low. I don't know; if the car was fully warmed up to top operating temps or what the ambient temps were outside at the time. Normal operating temps are in the 190-210 f range; you might have a soft or stuck open thermostat or a bad intake temp sensor, if you see low temps when driving a fully warmed up engine. 

In this case; I think, looking at live data and possibly logging things, would be more helpful. As noted before; the cat aging test, coolant temps and 02 sensor activity would be things to look at. 

Some people; have had problems with aftermarket cats, not able to work at the same level as the oe/oem versions and thus the trouble code. Knowing the cats efficiency through the use of the aging test and looking at the operating temps, could give you a sense of how it is working.

http://wiki.ross-tech.com/wiki/index.php/16804/P0420/001056

Looking at the info about the trouble code; here are things to check (again), to see if they are in spec: 

Possible Solutions

Check Intake and Exhaust System for Leaks
Check Catalyst
Check Oxygen Sensor(s)
Check Oxygen Sensor(s) Control
Perform Oxygen Sensor(s) Aging Check

If you have legit copy of VCDS; I highly recommend that you join the support site, they could look over your info/logs and give you expert info/analysis about what your problem could be. 

Start by registering and posting in the "new user forum": 

http://forums.ross-tech.com/

You might seek pro help; if things get beyond your ability to figure things out.


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## Slaghammer (Feb 8, 2016)

*Problem Solved!!!*

So, after shotgunning parts, I finally got the car to pass emissions. I put the original Cat back on... As near as I can tell, the MAF was going out (13% long term adjustment) and I created a new problem by using an aftermarket cat. Unfortunately I replaced the MAF with an aftermarket cat in place, so I couldn't see an immediate benefit. Now what to do with the two fail cats...


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## billymade (Jan 29, 2008)

Wow, sounds like a conundrum! Glad you got it worked out; maybe sell the cats on ebay or try to return them for a refund? :banghead: :facepalm: That is good news; you passed your smog test! Good job with the troubleshooting and repairs! eace:


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