P2680 indicates the engine control module (PCM/ECM) has detected an abnormally high voltage signal in the coolant degassing valve control circuit. This valve is part of the cooling system and helps release trapped air or excess pressure, typically controlled by the PCM via a relay or direct output.
The valve itself may be stuck, corroded, or internally shorted, causing a high-voltage condition in the control circuit.
Damaged, frayed, or shorted wiring between the PCM and the degassing valve, or a poor connection at the valve or PCM connector.
If the system uses a relay to control the valve, a stuck-closed relay or internal short could cause a high-voltage signal.
Moisture or corrosion in connectors or wiring can create a high-resistance or short-to-power condition, mimicking a high-voltage signal.
A shorted or failed output driver in the PCM/ECM could cause a high-voltage condition, but this is uncommon and should be diagnosed last.
No, the PCM/ECM is rarely the cause of this code. The issue is almost always due to a faulty degassing valve, wiring problem, or relay failure. Replacing the PCM should be a last resort after all other possibilities are exhausted.
Driving with this code may lead to engine overheating or coolant system issues, especially if the degassing valve is not functioning properly. It is recommended to diagnose and repair the issue as soon as possible.
Testing methods vary by vehicle, but generally, you can use a multimeter to check for resistance or continuity in the valve’s solenoid (if applicable). Some valves may also be tested by applying 12V directly to the terminals to verify operation. Always refer to manufacturer specifications.
The degassing valve helps remove air pockets from the coolant system, which can form after coolant refills or due to system leaks. Air pockets reduce cooling efficiency and can lead to overheating or poor heater performance.