Greetings. This code isn't new here, but it seems every instance is a little different. Here's my sitch, maybe you have some insight:
1999 4Runner SR5 / RWD
3.4 V6, 135K miles
California Emissions (and living in CA)
P0420 came on several times now.
Front A/F sensor & rear O2 sensor heater resistance checks out.
Pretty sure I don't have a vacuum leak.
Engine runs fine, good power.
Mileage has suffered recently a bit.
After the engine is hot the front A/F sensor stays fairly close to 0.65V. Short term trim is near 0% on the front A/F sensor. When I snap the throttle and/or rev the engine the A/F reading moves up / down by about 0.1V, but not more than that. (Seems a little on the low end of variation).
I've had a bit of inconsistent behavior from the rear O2 sensor. First time I checked it was fluctuating widely, suggesting the Cat was bad, but I did not do a thorough warm up (couple minutes at idle). This second time, I let the engine warm up a lot longer and rev'd it at 2500 RPM for 3 minutes per the FSM. Then the rear O2 reading varied quite slowly from about 0.3V to 0.7V.
The trim on the rear sensor is +100% which is definitely worrisome!
The front & rear sensors are Bosch, which I now know is not the best choice. They are probably 2-3 years old.
Since I'm in CA a front & rear CAT will set me back about $600 (I do the labor) whereas a new pair of Denso sensors will be about $150 total.
Any ideas how to make a dead-nuts diagnosis on this one?
Much appreciated!
-Jonathan
1999 4Runner SR5 / RWD
3.4 V6, 135K miles
California Emissions (and living in CA)
P0420 came on several times now.
Front A/F sensor & rear O2 sensor heater resistance checks out.
Pretty sure I don't have a vacuum leak.
Engine runs fine, good power.
Mileage has suffered recently a bit.
After the engine is hot the front A/F sensor stays fairly close to 0.65V. Short term trim is near 0% on the front A/F sensor. When I snap the throttle and/or rev the engine the A/F reading moves up / down by about 0.1V, but not more than that. (Seems a little on the low end of variation).
I've had a bit of inconsistent behavior from the rear O2 sensor. First time I checked it was fluctuating widely, suggesting the Cat was bad, but I did not do a thorough warm up (couple minutes at idle). This second time, I let the engine warm up a lot longer and rev'd it at 2500 RPM for 3 minutes per the FSM. Then the rear O2 reading varied quite slowly from about 0.3V to 0.7V.
The trim on the rear sensor is +100% which is definitely worrisome!
The front & rear sensors are Bosch, which I now know is not the best choice. They are probably 2-3 years old.
Since I'm in CA a front & rear CAT will set me back about $600 (I do the labor) whereas a new pair of Denso sensors will be about $150 total.
Any ideas how to make a dead-nuts diagnosis on this one?
Much appreciated!
-Jonathan
