On-Board Diagnostic System

The CIS-E control unit monitors emission control components that either provide input signals to or receive output signals from the control unit. Malfunctions or failures of any of these units are indicated by the "Check Engine" light on the dashboard and codes are simultaneously stored in the ECU memory.

On California models, an on-board 8-pin test connector is located in engine compartment by the firewall on passenger side or on the left fenderwell on 560SL models. Test connector is equipped with a push button and a Light Emitting Diode (LED). To activate on-board diagnostics, turn ignition on. Press push button for 2-4 seconds, LED should start flashing. Cause of malfunction is indicated by the number of blinks/flashes. By pressing push button again for 2-4 seconds, a further possible malfunction (code) will be indicated. If no other malfunctions (codes) are detected, the CIS-E control unit switches over to the on-off ratio readout.

Each code stored in the memory must be erased individually. After blink impulse (code) readout, wait 2 seconds then press push button for at least 6 seconds. LED will blink once, indicating code is erased. Continue until all codes are erased.