I have been running on regular unleaded for the last seven months (7000 miles) with no issues until recently when the check engine light turned on. I decided to put super unleaded in the car and after about one-hundred miles the light turned off. I'm currently on a trip and have racked up about 1200 miles but the light did not come on till I filled up halfway through the trip in a different state. Early today I filled up with super unleaded and after about an hour the light went off. Am I stuck running super to keep the CEL off?

 

It may be coincidence or any number of things, like an O2 sensor on its way out. To know what is causing this, go to a parts store and have the codes checked.

 

is your s40 turbo'd? If so I highly advise you to only use premium unleaded fuel, you need the higher octane levels for your turbo and engine to run efficiently...

 

The light is off now so I can't read the codes since they are no longer in the computer. Yes this a turbo 1.9L (aren't they all?) and I've been running regular for about six months in the car with no issues. One of the guys I work with has the same car and also runs regular with no problems. I thought maybe bad plugs but the O2 sensor is a possibilty. Yesterday the "Service" light came on for a few minutes and then turned off.