Check Engine Light on 01 S40 Volvo

The check engine light on my 01 S40 Volvo has been on for 6 weeks. I brought it to my repair guy - the code read faulty 02 sensor. We replaced one, then still got code, so we pulled out and put a new one in case it was faulty. Still got code, so we replaced the other 02 sensor. My guy thinks that the only thing that it can be is a faulty control module. He ordered me a used one, but I had to take to Volvo to put it in. Volvo looked at car, ran a ton of tests, and told me that it was a “undiagnosable problem”. Volvo tech said not to replace computer. I decided to wait a bit to see what code reads in a month or so, but I doubt that it will be any different. Has anyone else had this problem? I have stumped two shops, am out $750 and still have the light on! It’s making me hate my car!

It would be nice to know what the error code was. The trouble could be with the ECU, the wiring to the O2 sensor, or possibly the in the power to the ECU. Some one with good electrical troubleshooting skills should be able to find the trouble.

Thanks for your response. Unfortunately, the only thing that I know about the code reading is that it is always the same thing - bad 02 sensor. It kept saying that after we replaced both of them. Interestingly, after the work was done, the light always came back on within 50 miles and when I was driving at 55 mph or higher. Everyone is stumped. Volvo said that the control modules don’t usually go bad and they don’t think that this is the case b/c they are still able to communicate with it. (And their tech, who just won an an award for one of the best in the country, can’t figure it out - even a call to their “Volvo hotline” didn’t work).

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Regarding warning lights:

  1. if the coolant temp light comes on, shut off the engine ASAP

  2. if the oil warning light comes on, shut off the engine ASAP

  3. if a FLASHING MIL/CEL comes on, shut off the engine ASAP

    ASAP means driving to the berm of the highway right now and not waiting for the next exit.

But if the MIL/CEL is not flashing, then it’s not an urgent indicator.

Top 10 Things That Will Trigger the Check Engine Light on a 2001 Volvo

  1. Circular rotation of the wheels
  2. Circular rotation of the earth
  3. Wireless signal received from mechanic?s bank: ?Mortgage payment due on Ft. Meyers time share?
  4. Swedish holiday VALBORGSM?SSOAFTON
  5. Starting the car
  6. Flimsy 10-cent radiator hose fitting gives coolant an exit strategy, which causes engine to get so hot so fast that even former Chernobyl control room operators run away like toddlers chased by bears
  7. BP is probably involved somehow
  8. Not feeling so good today, will have to miss work
  9. Could it be the pulsing, quivering, throbbing steering wheel?
  10. Like any Swede, car is simply being prudent, in this case about need for reliable transportation

by Jeff Sawyer,