My queston is this. Is there any running conditions that would cause a rich condition that would not set off the MIL light? Only thing ive found so far is a loose TPS switch. I assume that MIL/ECM is working as they should, I can pull a code 12 properly, and within the last month or 2, it did correctly indicate a "32" which is what I found needed diagnosing.

Any help appreciated, Im hoping to avoid taking it in, but I only get two (after fail) all expense paid trips to the sniffer.

Scott

 

A weakening or contaminated oxygen sensor will create a rich condition, yet will not set a MIL (since the O² sensor is the only thing reporting exhaust gas oxygen to the ECM). If all other avenues are exhausted (no pun intended) you might try a fresh O² sensor. If the old sensor is 30K miles old or more, it may be time for one anyway.

 

OK, may replace, replaced 2 yrs ago, about 14K for miles. What would contaminate on O2 sensor? Would burning a little bit of oil do it? (leaky valve seals) Also had the cat replaced, about 3 yrs ago, less than 30K miles.

Thanks!!

 

Age, oil contamination, and escpecially coolant contamination and incompatible RTV type sealants will "kill" an oxygen sensor rather quickly. You can remove and test the existing sensor if you like. Connect a voltmeter and expose the sensor tip to a p[ropane flame. The sensor should produce at least 0.9VDC in the presence of a propane flame and drop to below 0.1VDC within a few seconds of being exposed to normal air (no flame).