Check Engine light solved - for winter people

[Glenn 328is]

I plug my car in during the night. And I noticed that when I start the car and leave it plugged in, the check engine light comes on. At first I was worried because I didn't know what happened, but it went off after 4 starts. I did it again, and again the CE light came on. And after 4 starts it went off again. Why does it not like having it plugged in while running? My other cars didn't seem to mind? Now I know though......

[bungy42]

Well, I bet that the alternator doesn't like battling the charger. Both of them are trying to charge the battery at the same time. Although I agree with you, I've never had this type of problem on any other car. BMW's electrical system must be more sensitive than most.

[jsp98m3]

I'm assuming you are talking about a heater for the water hose on the radiator etc?

The car is probably confused about the various temperature sensors not agreeing with each other when first started.

[Glenn 328is]

I'm assuming you are talking about a heater for the water hose on the radiator etc?

What are you referring to here Jim? I am talking about the block heater being plugged in....the only thing the block heater does, is warm the block up - the corresponding oil and anti-freeze - making it easier to start.

[jsp98m3]

Exactly. Most check engine lights are caused by some sensor being out of the expected range.

If one part of the system sees 60 degrees and another part of the system that should see something within 10 degrees of that reads 20 degrees then the ECU may throw a soft fault complaining about there being an unexplained temperature differential.

That's all I'm saying. It may not even be true. But it is an explanation. If it takes 4 run cycles to get the light to reset then you can probably satisfy your curiousity by having someone with a code reader pull the codes out of the ECU for you.