Well I have a month truly to clear them before I go to the emissions test. Of course, I cleared them with the tester, but they will come back. Here is what I know. I used my OBDII tester and pulled the following codes:

P0133 O2 sensor CKT slow Response ( bank1 sensor1)
P0171 System too Lean (bank 1)
P0420 Catalyst efficiency below threshold ( Bank 1)

What does it all mean?

 

the codes are pointing to the rear O2 sensor not responding fast enough. With that said, sometimes there can be an air leak (ie vacuum lines, intake tubing boots) or dirty intake parts (MAF, idle air valve, throttle body) that can throw the mix just off enough to trigger a code that blames the sensor. My suggested first step would be to check vacuum lines/trees/connectors and the intake tubing (you can spray carb cleaner etc to see if anything gets sucked that bumps the idle) then if you find nothing, check/clean the MAF, IAV and intake (use MAF cleaner - not carb cleaner as the filaments are sensitive). Finally you may need to replace the rear O2 sensor - also read up on whether your year may have a bulletin where an insert may be recommended to move the sensor out a bit... (I think that may be the 02s but can't recall).

 

It has been a week. I did check for vacuum leaks. I hate that job. I NEVER find any. I have an 85 VW with CIS injection and a type 4 air cooled with L-jet and I NEVER find any leaks. I hope that is cause I don't have any....

THis is my first car with turbo. The air leaves the cleaner box and goes into a large corrugated pipe and heads down to around the turbo. If there are leaks down there, i will need to lift the car.

I have MAF cleaner and gave it a shot.... I am not sure what "IAV" is. Can you help?

After i checked the codes last week, I cleared them. Today I have no CEL but the 420 code is pending. all the rest stayed clear.

 

IAV is short for idle air valve, aka idle control valve... it sits right near the MAF near the throttle body. You can probably find some vids on youtube for cleaning up the intake, you should do the MAF, the intake to the throttle body and the idle valve. LOL agree on vacuum leaks (never did fix my 84 Audi - I still have an idle valve for that car on my parts shelf!). Sometimes you need to have a smoke test particularly for the tubes and elbows that hide under the intake manifold. The air path you want to trace is from the turbo into the intercooler (part of the radiator set up) and up into the throttle body.

 

I have ordered the IAC gasket and I cleaned the MAF sensor with the proper cleaner.


I noticed the CEL light was back on. I guess the 420 code is NOT pending anymore. I will pull the codes again and see if any others are pending. But maybe the MAF cleaning cleared up the others.

 

BTW: I bought a CEL boss and it solved my problem. just mounted it in the exhaust boss, cleared the code and the code never came back. and of course I passed emissions.

 

Thanks for the update. I think you proved that the upper cat convertor is still working fine. I used the CEL Boss on my 2001 to get rid of the same annoying code.