Originally posted by NJE96SE:
I have researched this, and I think I have it right - I am just looking for a confirmation from the knowledgeable people round here.

Downstream O2 sensors are used solely for monitoring the pre-cat efficiency, correct? The upstream sensors help coordinate the MAF with the fuel injectors by telling the PCM if the exhaust gas is rich/lean. The downstream sensors get a value for O2 concentration that the PCM uses to compare to the upstream sensor value and determine if the pre-cat is oxidizing the nasty stuff. Am I semi-correct here?

The reason I am curious is that I have a downstream sensor that is bad. Can I get a set of MIL eliminators (a pair is cheaper than a single O2 sensor) and plug those in and forget about downstream sensors for good? Do you need a functioning O2 sensor for the MIL eliminators to work?

Thanks in advance for you help.




Mine went bad to, got it fixed Friday though. Also had the mechanic clean the MAF.

Did you get code PO171- to lean bank 1

That is what I had and he said the problem was the downstream O2 sensor.