1992 965 110K mi.
I am having trouble with a code 2-1-2,O2 sensor code. I tested the sensor and it
was questionable so today I replaced it with the OEM Bosch part, cleared the codes and all was well…. for about 6 miles. Now the "Check Engine" light has come back on. Have not checked the code yet, but I am sure it is the same. The car runs good,idles good, good fuel mileage and has no drivability problems. What should I look for next? Any and all help is welcomed and greatly appreciated.
Thanks Rob. F

When you checked the O2 sensor, what made you think it was questionable. I beleive the voltage readings should be between .1 & .9 volts and if the signal goes high(1.1) or low(.09) for too long a period or if the sensor voltage does not delivers its average 0.5V (signal absent 3 minutes after the engine temperture reaches 167F and a certain amont of load has been experienced then you get a 212 code.

Signal too high
signal lead short-circuited to live
Defective O2 sensor

Signal too low
Signal lead short-circuited to ground
Defective O2 sensor
Air leakage or fuel pressure too low
Faulty MAF sensor signal

Signal absent
Break in signal lead
Break in power lead
Break in ground lead
Contact Resistance in connections
Defective O2 sensor

Fault Sympton
High fuel consumption

Don't use releasing spray or oil on the O2 sensor connection

This should help you get started on finding a solution. Good Luck

I replaced my sensor based on the advice of the mechanic working on the car and still wound up with 2-1-2 codes. Sometimes like you within 6 miles and other times 100 to 500 miles. The true problem turned out to be a bad connection in one of the relays next to the DTC( one of the relays was reported bad so I went ahead and replaced both) and once that was corrected, I haven't seen the code in 5 months.

Jerry
Thanks for the reply.
I suspected the O2 sensor because it did not react correctly with an induced lean condition.
This may have been from me not knowing how to correctly use the old digital multi meter I was using and the inability to find the directions.
Any way I figured with 110k Mi. and 10 years it was only a matter of time any way.
I am sorry, what is the DTC. Are you referring to the two solenoids near the diagnostic
Connection?
Thanks again
Rob

Yes I am referring to the two relays next to the diagnostic trouble code (black box with a wire attached on the outside. One relay is for the injection valves and has red(comes from the battery), blue-yellow tracer, green -red tracer and solid black. The other relay goes to the coil paks and has red(comes from the battery) blue, and two solid black. Hope this clears up any question you have.

Thanks Jerry
I checked the connections on these relays today and cleaned then up and
put them together with a little grease. Now I will keep my fingers Xed. And hope for the best.