Not quite true. Yes, different parts numbers, not interchangeable. Front is a wideband O2 sensor, the rear is a narrow band O2 sensor. ECU looks for different electrical ranges from each, and while they share the same socket and same wiring connector, the same voltage reading from each means something different to the ECU.

When the brand is the same between the two, the front O2 should be the more expensive one. I don't have the part numbers on hand to provide them.


Incidently (since this was my thread originally), my front O2 sensor was in deed shot at the time, replacing it helped. My failed cat did it's damage to the engine as well, and it took another 40,000 miles for the compression to drop below minimum spec from the slow coolant leak.

 

For the record, the rear o2 sensor can affect mixture. If it reads lean it will drive the commanded AFRs rich. Seems to be more of a safety feature than a control function. If disconnected it will not effect anything other than a CEL. So if you suspect an o2 sensor and can't/don't want to decipher logs, disconnect the rear and see if millage/performance improves.

 

^ understood. I've learned a bit from your recent trial and error efforts