My check engine light on my '89 300 SE came on two days ago. I disconnected the battery, with made it go out, but it came back on within about 15 minutes. The car starts, runs and idles perfectly. I can't detect any fault. I checked the duty cycle and it's right at 50%.

I spent many weeks tracking down a start,stall,start,stall,start,chug-chug,run fault, during which I replaced many parts, the last was the injectors, which cured the problem.

Where do I start to find out why the CEL is on, when the car is running perfectly? Any hint as to where to start would be greatly appreciated.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire