The Diagnostic Module (DM) stores the car's malfunctions (called DTCs) and when they get over the 'threshold', the CE lights.
Go to my web page (click on the 'www house' below) and look at menus # 1, 2, 3 for the rationale behind the CE light. Menu #6 shows the codes stored in the DM. Strictly speaking the codes for your car will be different than those shown but there is a lot of similarity.
Under Menu #2, a LED/switch combo is presented: you can use that to read out the DTC(s) stored in the DM. Follow the procedure outlined, then let me know, we'll you what the problem is.
Regards . . . . JimF
'94 S500 Cpe
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