I have this 94 940 wagon. Had a rusted out exhaust. had it replaced. I still get a CEL light after about 45 minutes of driving. I pull off the battery lead. reset the light every few days. My question is why does it seem to run worse after the cel comes on? What does the CEL do to the volvo's brain? Mike

 

In order to answer your question you need to know what codes are being set with the ECU computer. Next time the CEL comes on have someone check what codes were set. Once you find out there will be a better chance of finding what the problem is. If the car starts running worse when the CEL comes on it may be going into limp mode. If that is the case you might be getting a significant problem. The CEL is the result of a engine sensor not functioning correctly. Check the codes.

 

I don't think the CEL causes the engine to run poorly, rather when the engine runs poorly due to some malfunction, the CEL does its thing and informs that something is not right... What codes are coming up? Many cars run fine with CELs on--not to say CEL is not important but they definitely may be overkill in some cases, and they don't affect anything just by being on...

 

Not true. A CEL is set when a sensor malfunctions or is out of it's spec. range. If it is an error due to weather related or a gas cap conditions then it will not necessarily cause an immediate problem. If it continues then something will fail. The longer you wait to resolve it may create a bigger problem. Then again in most states you won't pass inspection unless the CEL is off.

 

lets see. I think it idles rougher when the CEL comes on. Like you said" The CEL should just tell you there is trouble" I don't really notice a big loss in performance when the cel comes on. One thing seems that the exhaust has more water vapor, Like when you start the car up on a cold morning. when the CEL is on. Of course it is a big 940 so performance is hard to measure sometimes. I got the cel today and reset it. So if it goes off wed, I'll read. Before I got the exhaust fixed. it was 3 codes. Lambda, lean mixture and something MAF. The cat was rusted all out so of course it was reading lean with all the fresh air.

Just for kicks What does the 940 do to it self when it goes in limp home mode? SC

The c a t is gone. the O2 sensor is in the exhaust pipe. SC

 

Just ordered a o2 sensor off ebay for $23 bucks. Seems like if the cat was rusted out the O2 sensor would be shot. stay tuned. SC

 

A limp home mode uses a fixed set of engine parameters allowing the engine to run. It will not optimize the air/fuel mixture so you will loose some performance as well as getting poor fuel mileage.

 

yep, the best mpg I have gotten is about 19 and I'm running it at 2k rpm all time. hardly ever go over 50. The front end shakes if I goto fast.

The CEL came on quick this morning. it was foggy. code was 222 main relay. I dont know which one is the main one. After work , I flicked them all hard with my finger and wiggled them in the socket. reset the Cel. after about 2 miles it came back on 113 heatset o2 sensor max enrichment sensed. What do you think? SC

 

The O2 sensor came in and its is installed. the engine is smooth and the exhaust smells better. No CEL so far. Cheers thanks Sc