My '94 850 has been throwing codes 143(front knock sensor) 443(rear knock sensor) and 153(rear o2 sensor) for as long as I've owned it, which has been the last 3 years. It's a salvage job, and the ECU has probly always been thowing these codes, as they gentleman that sold me the vehicle had the Check Engine light wired to the Radiator light... yeah nice guy... ANYHOO... Last week I replaced my knock sensors and cleared the codes. Life was great with no Check Engine light untill today when it came back on, and sure enough, codes 143, 443 and 153. (yeah, I almost had an aneurism) So my thoughts are this:
Maybe its not the sensors, but the ECU? With the codes clearing, the Rear O2 sensor should have thrown a code by itself, but didnt, and then, when the codes do return, this is included.
Or even worse, a faulty relay cable buried somewhere deep in the guts of the car? (possibly damaged when the engine was reinstalled) Has anyone heard of the ECU acting this way? Any input would be greatly appreciated, y'know, before I turn into the Incredible Hulk and throw my volvo accross the river. [sm=wtf.gif]
-Thanks

 

I have seen 2 cars have a bad ECU and throw those codes.

 

I would have to side with Tech. If you had a wiring problem, the codes would set quickly. My 93 would set various transmission codes 3 to 4 times a year until the transmission module was replaced. Make sure you purchase the same part number for the module if you choose to replace it. Good luck!

 

Thanks guys. I'll get a new ECU and let you know if that was the problem.
Thanks again!