P0687 means ECM/PCM Power Relay Control Circuit High. The main power relay control circuit is reading high, which can mean the relay is staying on after the key is off. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0687 means
Modern vehicles have many control modules that share information over a network, usually called the CAN bus. Codes starting with U mean a module has stopped hearing another one, and voltage and processor codes mean a module is not getting clean power or has an internal fault. Low battery voltage, poor grounds, blown fuses and damaged wiring cause many of these codes, so test the battery and charging system first.
P0687 symptoms
- Battery drain overnight
- Check engine light
- Possible stalling
Common causes of P0687
- Stuck relay
- Control circuit shorted to voltage
- Corroded socket
How to diagnose P0687
- Check whether the relay stays on with the key off
- Test the relay
- Check the control circuit
Can you drive with P0687?
Usually yes, but watch for battery drain.
P0687 tips
If the battery goes flat overnight, listen for the main relay clicking off after the key is removed; a relay that stays on drains the battery.
Will P0687 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0687 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0685 | ECM/PCM Power Relay Control Circuit/Open |
| P0686 | ECM/PCM Power Relay Control Circuit Low |
| P0562 | System Voltage Low |
Guides that help
When it is more than a sensor
Voltage and network codes come from wiring, the battery, the charging system or a module, not from engine or transmission wear. If a lost-communication code has left the transmission in limp mode, rule out the module and wiring before deciding the unit has failed, and see our transmissions only if testing confirms internal damage.
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