I just recently got an 1995 850 Turbo, with 121K on it.

While driving to work (a 400 mile drive, I do it weekly), I got the check engine light. I pull off the interstate, check in the ops manual, and it says emissions issue.

No problem, I continue on. I have a B5234T engine. I discover the A2 socket, watch the blinking light, and I have a 4-3-6 error code, at least the way I read it, "Rear Heated Oxygen Sensor Compensation". However, that code is for the Fenix 5.2. According to vlvworld.com, the B5234T has the Motronic ECU, not the Fenix, and the Motronic doesnt have (well, I cant find it if it does), an error associated with 4-3-6.

Also, what the hell does sensor compensation mean anyway? Other than that, it runs just great.



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91 740 Wagon (RIP) 138K / 95 850T Wagon 122K and climbing (HMC member)

The 436 is for ALL models, and says the rear O2 sensor has maxed. Try reseting it, if you haven't already and put some good brand name gas in your tank.
Klaus
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98 V70Rawd(108Kmi), 95 854T(88K mi), 75 164E(173K mi)

I am not at work right now so I do not have access to all of my manuals and stuff but typically if you are posting a rear O2 sensor code it is indicative of a bad cat. The rear sensor is there for one reason only and that is as a reference sensor for the front one. When the rear sensor starts to read like the front one it interprets that as the catalytic converter is not doing it's job. The sensor signal varies with the amount of oxygen in the exhaust gas content and the cat uses that O2 to catalyze the other gases. So the O2 levels going in tend to peak and valley and when they come out they are much more of an even level so the front sensor typically bounces up and down and the rear is a flat line, when the rear starts to bounce up and down like the front then it determines that the cat efficiency is falling off. Fenix may post other codes for the rear O2 (why I don't know) but the only LH and Motronic codes I have seen are for the rear O2 are for catalyst efficiency. Hope this helps a little.

Mark