I have 94 850 Turbo wagon with a check engine light on - code4-3-3.When I have the codes checked and reset by my indy Volvo guy, the "check engine" light comes back on within a day, or a few miles, as you would expect. I was plannig to replace the knock sensors eventually, when I could afford the 500-600 bucks for the job. The mechanic I typically go to told me to make sure I use good fule, and that the knock sensor problem wasn't a big deal and no real threat to my engine.He did not think of that as an urgent matter to fix, but I might not be able to pass a smog test. I also thought the engine was knocking, but what do I know... Then I get the DMV registration renewal notice, requesting a "Test Only" smog check. So the check engine light is reset again, the next day I pass smog check successfully, and on my way home from thesmog station I get the check engine light on again, with code 433. Meanwhile, various people give me conflicting information regarding whether that's a big problem or a small problem. However, one day I had the oil sump seals replaced (with the engine sounding much better now) , and the reset check engine light did not come back on for more than 800 miles. Now is on again. I am thinking to replace these knock sensors, but now I am not sure that they are really bad. Otherwise why wouldn't the check engin light come on for 800 miles.

Any ideas about what the problem is and what should I check before changing the knock sensors? I would appreciate any suggestions and ideas! Thank you in advance.

 

I would change it soon. There is a set of updated sensors. Also I have seen the ECU's go bad and set that code all the time.