P0688 Mercedes-Benz Electronic Control Module Power Relay Control Circuit Open
Possible causes
– Weak battery- Low voltage while cranking
– Faulty Engine Control Module (ECM) relay
– Blown ECM fuse
– Faulty ECM
– ECM harness is open or shorted
– ECM circuit poor electrical connection
– Faulty Engine Control Module (ECM) relay
– Blown ECM fuse
– Faulty ECM
– ECM harness is open or shorted
– ECM circuit poor electrical connection
Tech description
Check all the ECM fuses, if the fuses are OK try replacing the ECM relay.
Symptoms
– Engine Light ON (or Service Engine Soon Warning Light)
Mercedes-Benz Vehicle:Mercedes-Benz C-Class,Mercedes-Benz CL-Class,Mercedes-Benz CLK-Class,Mercedes-Benz CLS-Class,Mercedes-Benz E-Class,Mercedes-Benz G-Class,Mercedes-Benz GL-Class,Mercedes-Benz GLK-Class,Mercedes-Benz M-Class,Mercedes-Benz R-Class,Mercedes-Benz S-Class,Mercedes-Benz SL-Class,Mercedes-Benz SLK-Class,Mercedes-Benz SLS-Class,Mercedes-Benz Sprinter 2500,Mercedes-Benz Sprinter 3500,