1991 Mercedes Benz 300CEFACTORY OEM SERVICE PROCEDURE

Clearing Codes

Disconnecting battery WILL NOT erase codes. Each code stored in CIS-E control unit and MAS unit memory must be erased individually. After malfunction code is displayed, wait 2 seconds then press START button for at least 6-10 seconds. LED will blink once, or impulse readout will display "=1", indicating code is erased. Continue this sequence until all codes are erased and only "=1" is displayed. Disconnect test equipment.

Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.