98 S70 N/A code 0422 (Cat efficiency)

Post by **FLXC90** » 27 Sep 2014, 09:23

History, purchased car with recent timing belt, water pump etc.. but battery was dead. New battery, working through kinks as I can. Replaced MAF yesterday for code 0102 and 1272. (vacuum system also rejuvenated) Did re-learn on ECU. this morning at 25 miles on the reset, CEL came on. First scan was P0001 (something about fuel trim-open?) second code was 0422. I know the car had been running rich both by codes, and by 15ish mpg. I was on my way to fill the tank and start logging mileage when CEL came on. I hope this code is really only symptomatic of the rich fuel trim history, and that the rear O2 sensor needs to adapt to re-normed fuel trim. Does this sound feasible? no bad smells, idle is smooth at 850-900, throttle response is good after recent tweaks. Car has 222k by the odometer, compression 170-180 across the board. (after 2 seafoam treatments).

Thanks

Patrick

Post by **rmmagow** » 27 Sep 2014, 09:55

It is the second O2 sensor that pops that code. Can you get a hold of a real-time streaming code reader (Torque on an Android with the ELM adapter would work)? You need to watch the voltage fluctuations of both O2 sensors, the front one should fluctuate a lot and with regularity, the second should be semi-stable with much lower amplitude fluctuations. If the second one moves a lot, that indicates the CAT isn't doing its job and is either bad or really dirty/clogged. If the front doesn't seem very active, it could be bad or going bad which would make the second one fluctuate too much. If you see this, a new front sensor might be in order or sometimes a good long high speed run can clean it a bit. The RICH history of engine running points to probably a sooted up front o2 sensor. I've heard of taking it out and burning off deposits with a blow torch, me, I'd just put in a new one and be done with it.

Post by **timmybdaddyof3** » 27 Sep 2014, 10:08

sensor can cause this and I have seen it a few times....are you sure you got the ltft's cleared and the computer was totally reset before you tried the relearn?

Post by **FLXC90** » 27 Sep 2014, 12:12

First, thanks for the response, I did the hard reset of the ECU as listed in the thread in this forum. Disconnected neg battery terminal, tapped brakes a few times to dissipate residual current, reconnected and performed drive profile, is there an additional step to clear ltft history aside from what I've done?