'01 GLX V6 5spd ATQ 160k
I have read numerous post related to these two codes, have had them both show up intermittently over the last two years, I am also getting some random misfires on all cylinders, some history -
I have had the 'ECU reflash' procedure, I had all four O2 sensors replaced(3 oem & 1 donor) and both CATs swapped from a donor car w 60k, I have replaced the coils( whole OEM part), Plug wires(OEM), and Plugs. I have replaced the air intake filter, fuel filter, Cleaned MAF + Throttle body, replaced Vac lines, EGR purge valve, EGR plastic tubing. I pretty sure SAIP is working properly.
Car runs fine(go figure), I use only 93, my daily commute is short(4mi) an I am in traffic mostly so the car never gets RPMs up much, I have never run the tank dry but have gotten it very low a few times. I have run some injector cleaner through it maybe twice in last two years.
I have heard short trips, over fill oil, run tank dry, SAIP broke, as all being 'possible' causes for symptoms I am experiencing with the CATs
With car started and running fine,I then log in to VagCom(409.1 shareware ver) and check engine module, I get all pass on the 'readiness' with the above codes showing *but* when I hit 'clear codes' it clears but then when I check readiness again it show most systems as 'fail' and car will start to misfire alittle?? <-- could VAGCom itself be causing something?
The CEL will stay off for varying amounts of time before popping back up, weird thing is I always get BOTH P0421 and P0431 every time at the same time. occasionally the other P03xx's will show up as well, never get any other codes than these, WTH??
Any suggestions on what else could I check or do about the misfires?
and the 'Cat below efficiency - intermittent' P0431/P0421 codes before replacing CATs (again)?
Oh yeh car ran fine before and after all above parts were replaced, no difference that I could tell, lol.
I love this car but DAM