The P0684 trouble code indicates a range or performance issue in the communication circuit between the glow plug control module and the powertrain control module (PCM). The glow plug control module manages the operation of the glow plugs in a diesel engine, preheating the combustion chamber for easier cold starts. When the PCM detects a discrepancy or inconsistency in the communication signals between these modules, it triggers the P0684 code.
P0684 Glow Plug Control Module to PCM Communication Circuit Range/Performance
Code symptoms P0684.
1. Check Engine Light (CEL) illuminated on the dashboard.
2. Difficulty starting the engine, especially in cold weather.
3. Rough idle or misfiring during cold starts.
4. Decreased engine performance and fuel efficiency, particularly during cold starts.
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 P0684.
1. Faulty glow plug control module.
2. Wiring or connector issues in the communication circuit between the glow plug control module and PCM, such as corrosion, damaged wires, or loose connections.
3. Faulty PCM.
Code Solutions P0684.
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 communication circuit between the glow plug control module and PCM for any signs of damage, corrosion, or loose connections. Repair or replace damaged components as needed.
3. Test the glow plug control module using a scan tool capable of bi-directional control to ensure it is functioning properly. Replace the module if it is found to be faulty.
4. If the wiring, connectors, and glow plug control module are in good condition but the code persists, it may indicate a fault in the PCM. In this case, the PCM may need to be replaced or reprogrammed by a qualified technician.
5. 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.
6. Follow manufacturer-specific diagnostic procedures outlined in the vehicle’s service manual to accurately diagnose and repair issues related to the communication circuit between the glow plug control module and PCM. If needed, seek assistance from a qualified technician or dealership.