P0686 means ECM/PCM Power Relay Control Circuit Low. The main power relay control circuit is reading low, as if shorted to ground. 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 P0686 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.
P0686 symptoms
- No start or stalling
- Check engine light
Common causes of P0686
- Shorted control wiring
- Failed relay
- Corroded socket
How to diagnose P0686
- Check the relay and socket
- Check the control circuit for shorts
Can you drive with P0686?
Not reliably.
P0686 tips
Check the relay socket for corrosion from water entering the fuse box, and check the fuse box lid and seals for damage. A low-circuit code points to a short to ground in the control wiring, so inspect the harness between the relay and the computer if the relay and socket are good.
Will P0686 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 P0686 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 |
| P0562 | System Voltage Low |
| P0606 | Control Module Processor |
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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