O2 Sensor Voltage

Hi Guys,
I need some help/advice form those of you with O2 sensor issues and/or cat replacement. My 2006 with 175k had a check engine light and the code reader said P0430 bank 2. I replaced the downstream O2 sensor with a new Denso unit, cleared the code, but the same P0430 returned after about 15 miles of driving.

Searched the treads and one mentioned the pre cat 02 sensor can go bad, but still throw a P0430 code, essentially tricking the post cat sensor into to thinking the cat is bad. Has anyone recently experienced this?

Any ideas? Thanks!

 

Yes, this can actually happen. The downstream sensor only monitors the cats and technically doesn’t know what the front sensor is or isn’t supposed to be doing. So... in a situation in which the front O2 is is reading wonky, the rear O2 will tell you that the catalytic converter isn’t keeping up with the fuel its supposed to be cleaning out, not realizing that there might be so much field getting poured into that bank due to the upstream sensor being bad, that it throws the rear O2 code. The ECM doesn’t know what the sensor is supposed to be at, since it uses it a reference for what is actually being expelled from the cylinders. Therefore, the ECM is only pushing out what the upstream sensor is telling it, not realizing that the rear O2 is actually reading correctly, but yet not matching what the upstream sensor is technically reading. Hopefully that makes sense.

Also, about the only true way to confirm that the sensors are reading wonky is with a data list. You have to watch the sensor modulation to be able to determine if its actually going bad and not just an air leak in the exhaust, for example.

 

Never had a check engine light go off for this, but when testing the rear original Denso o2’s I recently replaced (just because they looked old) I confirmed they were bad (per Ohms test in FSM). I replaced the 7 year newer Bosch fronts, as well, with Denso.