View Full Version : need suggestion for fixing cat ineff CEL (i've done research already, need direction)

09-29-2007, 08:18 AM
So I've had P0-430 (cat inefficiency) for a while and got it scanned again and now I'm getting P0-420 which is "cat inef below threshold" or something. i figure this is probably time to get this fixed as i've had this off and on CEL for the last year at least and i can tell when it comes back on (after getting it cleared at autozone a week or two later usually) the car doesn't drive as smooth.

i understand it could be any of the following:

cats going bad. if so, how do i tell? the scan should say "bank x" and that tells me which side right? any more info?
O2 sensors. same thing, does the scan say which bank = which side to give me a better idea? i know there's pre and post sensors on both sides. i'd like to avoid guessing if possible.
apparently there's a TSB about the ECM being too picky and throwing CEL. i'm out of the 8 year/80k mile fed warranty but, i'm in a 2001 2.8 so i'm assuming i would have the most recent flash right? dealership said they'd flash me for $70, worth trying that first?

i've heard of hitting on cats with a rubber mallet to see if they're bad, etc. what are some tips with the info i've given about that will help me pinpoint this problem w/o wasting money replacing diff things?

09-29-2007, 09:31 AM
you could try the flash first.

if you have VAG-COM you can log the front and rear 02 sensors.

the fronts should vary up and down, and the rears should be steady after the engine is fully warm.

if you see a similar fluctuation in a rear sensor similar to a front, it is most likely a bad CAT, although it could be an exhaust leak.

if everything looks steady on the rears, then one dips or spikes or stays very low, its probably that sensor.

09-30-2007, 08:52 AM
excellent info, thanks man. i can log all that with an ebay cable and software right? i've looked in to what can and can't be done w/ that and i think i'm safe saving money and getting that cable to do this.