I have a 2001 Volvo S40 2.0T...about 156,000 miles on it. Sometime in the past few months, I began to get an intermittent check engine light, then of late it has become a solid check engine light. I didn't notice any difference in the way the car has been running, but whenever the code was checked, it indicated the oxygen sensor (bank 2), so I finally broke down and had that replaced.

Check engine light is still on and still indicating the sensor.

I had Maxi perform an emissions test. There are no leaks (although they can't check the turbo), plugs are working, the oxygen sensor (the new one) is working...they couldn't find anything wrong.

I'm not going to throw money down a useless drain searching for non-existent problems, which I'm thinking is what is happening now. But I would like to figure out if there really is some issue, however minor, and I would also like to be able to clear the check engine light to be able to see something real when it does happen.

Has anyone who has had this problem successfully dealt with it? Please inform me how if so.

 

This may be a stupid question but did they erase all the stored codes when you checked the codes? And they replaced the bottom O2 sensor not the top one?

 

If by "bottom" you mean the one downstream, the one that usually gets replaced, yes. (Sorry, I'm not a big car person by nature, and I'm having to catch up on oxygen sensor lingo lately.) I'm not sure they erased it...they cleared it, twice. When I first picked up the car, it was clear and as I pulled out of the parking lot, the light came back on. I turned around, they checked the code, it was the same code, they cleared it again, and next morning, it came back. (This was done at an NTB.)

I called Volvo and they recommended I get the system pressure checked for leaks, check the plugs, and check the sensor. They wanted $85 for that...Maxi would do it for $39.95, so I went to Maxi. They couldn't find anything wrong so they didn't even charge me that, so here I am, trying to figure out what's really going on here.

I don't know much about cars, but I do know a bit about electronics in my distant past. I suspect that this code isn't about the O2 sensor at all, but something to do with the computer itself, or maybe the turbo, since Maxi couldn't check that. And so, here I am, looking for answers. I've also looked around a few other boards and seen several people who have replaced both O2 sensors and the problem persists, which again, leads me to think its something else and the computer is interpreting it (or misinterpreting it) as an O2 problem.

 

Ok, I haven't had this particular problem yet. I had a code set for the 1st O2 sensor. It's the top one before the cat converter. I bought the generic Bosch O2 sensor and spliced the old sensor's connector onto the new O2 sensor.

Our cars also have an extra harness between the O2 connector and the car's connector. When I traced out the wires it appears the extra harness switches one wire around. If you follow the wires from the O2 sensor they hide behind a little plastic cover on the firewall. Remove that and you can see if the extra harness is there.