Codes P0420 and P0171

[rigormortis]

My daughter's Beetle MIL light is on, throwing codes P0420 and P0171. Car seems to run fine, although every once in a great while she says it stalls.
Any suggestions on troubleshooting? O2 sensors? CAT? How do I check to see if it's an AEG engine that may still be under the extended CAT warranty?
I really appreciate any help!

[MyOtherRidesAVette]

Research your codes here (look for a common denominator) -
Category:Fault Codes - Ross-Tech Wiki

MORAV

[Smileybug]

Any AEG is going to be out of the extended warranty, which was 10 years/120k. AEG engines were from '98-2000. May have extended into 2001 cars, but it would have been the early '01 cars.

The P0420 does, more often than not, point to a failed cat. Notice any rattling? Poor MPGs? Sulfur smell?

[MyOtherRidesAVette]

FYI maybe. I believe the CAT warranty is 12 years (for all vehicles originally delivered) in CA. And the OPer hasn't bothered to give us any info or complete his/her info in the User CP.

M.

[rigormortis]

Originally Posted by MyOtherRidesAVette

FYI maybe. I believe the CAT warranty is 12 years (for all vehicles originally delivered) in CA. And the OPer hasn't bothered to give us any info or complete his/her info in the User CP.

M.

Exactly what kind of info do you want?? If there's something specific you want me to spell out, please tell me rather making a general statement that I haven't bothered to give you any info.

All I need is someone that may have had a similar experience with the same codes to maybe point me in the right direction, rather than spending hours on the internet or $$$$ a some shop or dealer .

[Smileybug]

Year of the car would be helpful, and mileage. And location.

[billymade]

If you want to know if the cat is under warranty; call your local vw dealership with your VIN #... they should be able to tell you over the phone. What year and model is your car?


16804/P0420/001056 - Catalyst System; Bank 1: Efficiency Below Threshold

Possible Causes
Leakage in Intake and/or Exhaust System
Catalyst faulty
Oxygen Sensor(s) faulty
Oxygen Sensor(s) Control faulty

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

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

My own experiences with this code: have been failed 02 sensors and obvious exhaust leaks; most commonly at the flex pipe before the cat (it looks like a large braided section that can flex when the engine moves).

As you can see; there are a number of possibilities, you need to start a step by step process of troubleshooting and eliminate the possibilities one by one. I would recommend getting the bently manual or possibly the cheaper haynes manuals to get you started in the process; if this is beyond your abilities, time, equipment or desire, I would seek out a competent vw indpendant shop to get your vw diagnosed and/or repaired. Good luck and let us know how things progress.

[MyOtherRidesAVette]

Originally Posted by rigormortis

Exactly what kind of info do you want?? If there's something specific you want me to spell out, please tell me rather making a general statement that I haven't bothered to give you any info.

All I need is someone that may have had a similar experience with the same codes to maybe point me in the right direction, rather than spending hours on the internet or $$$$ a some shop or dealer .

Easy. Just basic info, Year, Engine, not even series, just 2.0, 1.8. 1.9, Location, Just what would be in the User CP. We are not physcic. Location affects the length of mandated warraties on some items. Engine type affects how some thrown codes may apply. I do see that this is posted under the 2.0, so don't expend all the extra effort putting that into the User CP.

billymade went to the trouble of looking up one code for you, here is the other

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

Special Notes

• Fuel Trim Info

The common denominator between the codes is intake system leak(s), which may be your problem, or you may have multiple problems which would also initiate multiple codes. As these DTCs don't point to any one specific thing how could you expect any of us to know what the problem is. We are trying to tell you what you can do to find out WITHOUT spending THOSE big $$$$.

I guess, however, if you want to drive on over, I can start checking the other things for you.

M.

[rigormortis]

I just re-read my previous reply - My apologies if I came across as a douche, that wasn't my intention.

It's a 2001, 2.0, auto, ~113k miles, located just outside of Manassas, VA

No rattling or sulfur smell, and I don't detect any exhaust leaks.

I appreciate billymade and MORAV posting the code information ; I found the same things myself from the first link that was posted. That's where I needed the collective expertise from folks such as yourselves to help me sort through the large number of things that can trip those codes and maybe narrow down to a few things I can check myself before taking it to a shop.

[MyOtherRidesAVette]

Originally Posted by rigormortis

I just re-read my previous reply - My apologies if I came across as a douche, that wasn't my intention.

I appreciate billymade and MORAV posting the code information ; I found the same things myself from the first link that was posted. That's where I needed the collective expertise from folks such as yourselves to help me sort through the large number of things that can trip those codes and maybe narrow down to a few things I can check myself before taking it to a shop.

First link posted was me, you know, the one you lashed out at! (lol)

No problem many of us are here to help, so be willing to help with anything that may be pertinent. Never know what may or may not be so filling out the User CP info makes it easier. Some problems can even be specific climate or elevation related. Sometimes A/T or M/T, sometimes even specific engine series, not size.

Check on the easy, no equipment required, things first. As I said, since there is a common denominator of intake leak(s), that is where I would start. I read about a lot of these around the MAF. If you need more help, even with doing that, post up. We can also help you with the more involved, that may require equipment and testing. Just don't start thorwing new parts at things as some do. Cheaper to have things checked if you get it narrowed down to that and can't or are not comfortable running the diagnostics.

M.

[MyOtherRidesAVette]

As an update, researching something else, I just learned that a leak downstream of the MAF will throw a P2187 code also, so I'd concentrate looking for a leak in or before the MAF.

M

[rigormortis]

Thanks MORAV, I appreciate the insight. I'll check around the MAF tomorrow and start looking in detail around the intake and vacuum lines for leaks. I can deal with that or one or both O2 sensors, but I'm really hoping it's not the CAT *fingers crossed, garlic around neck, and knocking on wood*

[Smileybug]

If it is the cat, you can get it replaced with an aftermarket unit for cheap. I had mine done last year for less than $200, parts and labor.

[MyOtherRidesAVette]

I'm going to make a generalized statement about a bad cat which is probably going to bring the rath of a few down on me. Cats don't just fail. They fail because the car was (mechanically at any rate) poorly maintained (like driving for months with a CEL on - I've read ppl wanting to kill the light so they could pass emissions), they fail from external damage, and they might fail ultimately from wearing out, but this doesn't happen naturally at 11 years and 115k miles. I have never had need to replace a cat, and I have had two vehicles to 440k miles, one to 375k miles, and I presently have two at 280k miles

M.

[Smileybug]

Mine was rattling, which is what the extended recall was about. No CELs, extremely well maintained and it wasn't damaged externally. It failed from the inside, as the honeycomb stuff just came apart. My car was at 11 years and 90k. Hubby's Honda on the other hand, at 173k and 11 years never had it replaced. And its maintained enough, but not tenderly cared for like our VWs With the AEGs, the cats were poorly made.

The cat may also fail gradually, but not throw a CEL right away either. Could have been on its way out for a bit with no CEL. Mine was rattling for probably 4 months or so before the light came on (I assumed it was a loose heat shield since I had no CEL and couldn't get it on a lift to check it out). Then the CEL finally came on with the P0420 code. Sadly, even though the mileage was waaayyy under for the extended recall and I had the exact symptoms that the recall was issued for, VW wouldn't do anything for me because it was just barely 11 years old.

[MyOtherRidesAVette]

Originally Posted by Smileybug

Mine was rattling, which is what the extended recall was about. No CELs, extremely well maintained and it wasn't damaged externally. It failed from the inside, as the honeycomb stuff just came apart. My car was at 11 years and 90k. Hubby's Honda on the other hand, at 173k and 11 years never had it replaced. And its maintained enough, but not tenderly cared for like our VWs With the AEGs, the cats were poorly made.

The cat may also fail gradually, but not throw a CEL right away either. Could have been on its way out for a bit with no CEL. Mine was rattling for probably 4 months or so before the light came on (I assumed it was a loose heat shield since I had no CEL and couldn't get it on a lift to check it out). Then the CEL finally came on with the P0420 code. Sadly, even though the mileage was waaayyy under for the extended recall and I had the exact symptoms that the recall was issued for, VW wouldn't do anything for me because it was just barely 11 years old.

Is this the recall you are talking about? I don't read this (looking at all the documents) as an extended warranty/recall type of thing. This is not a recall for a bad or defective part. This is a recall for replacement of a part for which the wrong part was installed. It is defined by VIN. I have attached the page showing the picture of both the wrong one and the right one.

MORAV

[rigormortis]

Here's the extended warranty/recall I think Smileybug is referring to: VW Catalyst Warranty Extension | Cars and Light Trucks | US EPA

While changing her front brake pads and rotating her tires, I went through the intake, cleaned the MAF, and changed the spark plugs (it was time anyway). I didn't find any obvious issues, and the car still runs about the same. There is a rattle from the underside when I rev the engine, but I haven't had a chance to get under it to localize it (football to watch, beer to drink )

I borrowed a scanner tool to reset the MIL; I'll see how long it takes to come back and see if it gives me the same codes.

[Smileybug]

If its rattling, its likely the cat. Could be a heatshield, but its likely the cat, especially since you are getting the P0420 code.