Code P0690 indicates that the engine control module (ECM) or powertrain control module (PCM) has detected a voltage higher than the expected range on its power relay sense circuit. This circuit monitors the voltage supplied by the ECM/PCM power relay, and a high reading typically points to a relay stuck closed, a short to battery voltage, or a charging system fault.
The most common cause. A relay that remains closed will supply continuous battery voltage to the sense circuit, causing a high reading.
A chafed or damaged wire in the sense circuit can make direct contact with a 12V source, bypassing the relay and causing a high signal.
Poor connections can create resistance or allow voltage leaks, but in this case a short across terminals is more likely; still, inspect connectors for damage.
If the entire electrical system is running at an abnormally high voltage, the sense circuit will also read high. This is less common but possible.
Rare, but the PCM itself can fail internally, causing a high sense voltage. This should only be considered after thoroughly testing all other components.
It is not recommended. The high voltage condition may cause erratic engine behavior, stalling, or even damage to the PCM or other electronics. Have the issue diagnosed and repaired promptly.
Yes, if you have basic automotive electrical skills. However, first confirm the relay is the cause by testing it. Replacing a good relay will not fix a shorted wire or overcharging alternator.
Very rarely. The PCM is almost never the cause of this code. Most cases are resolved by replacing a stuck relay or repairing a shorted wire. Only consider PCM replacement after all other possibilities have been ruled out by a professional.
It means the PCM is seeing a voltage on the sense wire that is higher than expected (usually above a calibrated threshold). This typically indicates the relay is stuck closed, a wire is shorted to 12V, or the charging system is overvoltage.