O2 Sensor Question

[Thecatmilton]

So one of my friends recently purchased a 1999 323i. The seller told us that the car was not recognizing the post cat O2 sensor. As in the computer can't see or detect it. The seller did replace the sensor, but it didn't make a difference. Has this happened to anyone else?

[All2kool]

The seller did replace the sensor, but it didn't make a difference.

If the seller replaced it with after-market Chinese crap, it's likely a failure of a new part. O2 Sensors on a BMW should always be a Bosch part. After-market crap can have an out of box failure rate exceeding 50%.

[Thecatmilton]

I don't know how or why, but we drove the car up on oil change ramps and the CEL went off. We are going to drive it a bit and see if the CEL stays off. We tried getting it inspected, but the battery was dead when we got the car so we need to drive it 100 miles first.

[MIKYZZ4]

Check for loose or shorted wiring connections hanging off the post-cat sensor under car.

[whiskychaser]

FWIW, I am working on two faults. Post cat heater doesn't throw the service light let alone CEL. But I know it is duff and am about to replace it. Lean on both banks just throws the occasional service light which I can turn off and it will not reappear for months. I have some new O rings to fix that. So maybe you need to read the fault codes and establish what the ECU thinks is wrong?