Does your car have the small black box with a red LED and a button on the frewall near the battery? If you hold down the button for 4-6 seconds, the LED light will flash the fault code(s). At least that's how my 89' 300SEL worked. My CEL would come on intermittently while driving, the problem ended up being a bad Air Mass Meter potentiometer.

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

If your car is Cal version, here are the codes ..

FAULT CODE TABLE

DTC Readout Possible Cause of Failure
1 No fault found
2 Throttle position switch - wide open throttle fault
3 Engine coolant temperature sensor
4 Air flow sensor position indicator
5 Oxygen sensor
6 Not used
7 TD-signal (rpm)
8 Altitude correction capsule
9 Electronic hydraulic actuator (EHA)
10 Throttle position switch - closed throttle position fault (idle)
12 Exhaust gas recirculation temperature sensor

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A Dalton

Mine was bought new in Florida, so would it have totally different codes?

I will look on Sunday to see if it has that. 88-89 should be identical, but since yours was a California car and mine is a Florida car, it may be different in that aspect? I will look though. Thanks!