Hello Fellows.

I have been chasing a P0133 for a couple of years now and really getting frustrated.

This code maps to both Volvo codes 435 (front O2 slow to respond) and 436 (rear O2 compensation - whatever that means).

I have replaced the front O2 sensor twice with the bosch direct-fit replacement and still get the code.

I am very sure I don't have any vac leaks, though I have not smoke tested yet (been meaning to make a DIY smoke tester but haven't gotten around to it yet). I have replaced every vac and PCV line on the car recently and see no wearing/softening/etc.

I am also very sure there are no exhaust leaks, though I have not smoke tested yet (see above). I have done the 'plug the end and look for smoke' test and see no exhaust escaping.


I did the test as described by tmannian (http://www.brickboard.com/AWD/volvo/1457038/850/code_436new_o2_sensor.html) in a recent thread about a similar problem. I found the rear O2 did NOT respond as predicted by the test. It read 0.48V the entire time no matter what I did to introduce a vac leak or make the mixture rich by clamping the return fuel line. I was able to watch both sensors output in real time on my scan tool.

"Great!" I thought. I'll just replace the rear O2 and be done with this.

I today replaced the rear O2 sensor with one that bench tested fine. I am not sure what the sensor I pulled is (maybe a walker?) but the one I put in was a bosch.

I then ran the rear O2 tests again and saw the EXACT SAME THING - 0.48 through all tests.

Any ideas about what's going on? The MIL hasn't come back on yet because I haven't really taken the car anywhere (down the road to the in-laws). I suspect it will though.

Does this point to a bad CatConv? A bad FPR?

Any and all ideas are welcomed.
--
1998 V70 AWD->FWD Turbo 200k+