I recently had an issue with an ignition coil on cyclinder 1 of my 2002 A4 1.8L (83K) and replaced all four replaced along with the spark plug. Drove it for a few days and got back a catalyst efficiency is below threshold code from the obd2 reader. I have been resetting the code for the last two days or so. The CEL light seems to come back on every second drive cycle. It is good on the fist drive, stop go and 55+ drive for a long period of time. The second time I start it and get it to operating temp (10-15 mins), the CEL comes on and code is shown.

I am not sure if my theory hold true but does it sound like the cat converter is bad? I have NO smell of rotten eggs, noise, lack of power or smoke. I talk to the dealership on the phone and told me that most likely it is the cat converter (~$2000 repair from them). I was thinking it might be the first or second 02 sensor might be bad (no O2 code is showing) and/or the difference between the two might be off? I do not want to put dump all that money into a cat. Any ideas on how to test or what to do? I've been running some carbon cleaning products to clean out the system. I need to get this car passed for the emissions test via a OBD2 method. Problem is, I can't get all the sensors to be "ready" for the test.

Any help would be much appreciated.

 

oh ye, check the voltage from the oxygen sensors first, then if its good thne probably the CAT, go with universal one.

 

Its the cat if there is no o2 sensor codes

And codes will only set the CEL if the computer sees a fault for two drive cycles in a row

 

replace it with a test pipe and do the diy no codes fix. If you got to replace it yo might as well get some power.

 

What is the diy no codes fix? If I do that will I still pass a state emissions test using the OBDII method?

Also, any suggestions on how to do the bent pipe? It sounds like a sweet idea!

 

yes, you will still pass the obdII emissions testing because there is not a smog tester. Look at it in the diy part.