The P0688 trouble code indicates an open circuit in the power relay sense circuit of the Engine Control Module (ECM) or Powertrain Control Module (PCM). The power relay sense circuit is responsible for monitoring the voltage output of the ECM or PCM power relay. When the ECM detects an open circuit in the power relay sense circuit, it triggers the P0688 code.
P0688 ECM/PCM Power Relay Sense Circuit Open
Code symptoms P0688.
1. Check Engine Light (CEL) illuminated on the dashboard.
2. Engine may not start or may experience difficulty starting.
3. Engine may stall or hesitate during operation.
4. Decreased engine performance and fuel efficiency.
5. Other related trouble codes may be present, depending on the specific issue.
This code is common in brands such as:: Chevrolet, Renault, Ford, Toyota, Nissan, Mercedes Benz, Honda.
Causes of the code P0688.
1. Faulty ECM or PCM power relay sense circuit.
2. Poor electrical connection in the power relay sense circuit.
3. Open or shorted wiring in the power relay sense circuit.
4. Faulty ECM or PCM.
Code Solutions P0688.
1. Use a diagnostic scanner to retrieve freeze frame data and all associated trouble codes. This information can help pinpoint the root cause of the issue.
2. Inspect the wiring and connectors in the power relay sense circuit for any signs of damage, corrosion, or loose connections. Repair or replace damaged components as needed.
3. Test the ECM or PCM power relay sense circuit using a multimeter to ensure it is functioning properly. Replace any faulty components.
4. Check the voltage at the power relay sense circuit using a multimeter. If the voltage is incorrect or not present, diagnose and repair any issues with the power relay or related components.
5. If the wiring, connectors, and ECM or PCM power relay sense circuit are in good condition but the code persists, it may indicate a fault in the ECM or PCM. In this case, the ECM or PCM may need to be replaced or reprogrammed by a qualified technician.
6. After any repairs are made, clear the trouble codes and perform a test drive to verify that the issue has been resolved. If the code returns, further diagnosis may be necessary to identify the underlying problem.
7. Follow manufacturer-specific diagnostic procedures outlined in the vehicle’s service manual to accurately diagnose and repair issues related to the ECM or PCM power relay sense circuit. If needed, seek assistance from a qualified technician or dealership.