P0686
ECM/PCM Power Relay Control Circuit Low
P0686 is an OBD-II diagnostic trouble code meaning: ECM/PCM Power Relay Control Circuit Low. Common causes: short circuit of the relay control wire to ground, open circuit in the power supply of the relay control coil. Estimated repair cost: $6–111.
Symptoms
- Unstable engine operation
- Check Engine Light
- Possible spontaneous engine shutdown
- Malfunctions of the car's electronic systems
- Difficulty starting the engine
Causes
- Short circuit of the relay control wire to ground
- Open circuit in the power supply of the relay control coil
- ECU power relay malfunction
- Oxidation or damage to the relay connector
- Internal ECU fault
How to Fix
- Read OBD-II codes
- Locate the ECU power relay according to the diagram
- Measure the control signal voltage at the relay (normal: about 12 V with active control)
- Check control wire for short to ground
- Check the relay and its connector
- If the external circuit is working properly - ECU diagnostics
Related codes
Error P0686 by Vehicle Brand
FAQ
What does the P0686 code mean?
P0686 is an OBD-II diagnostic trouble code that indicates: ECM/PCM Power Relay Control Circuit Low
What causes a P0686 error code?
The most common causes of P0686 include: Short circuit of the relay control wire to ground; Open circuit in the power supply of the relay control coil; ECU power relay malfunction; Oxidation or damage to the relay connector.
How do I fix a P0686 diagnostic trouble code?
To fix P0686: Read OBD-II codes. Locate the ECU power relay according to the diagram. Measure the control signal voltage at the relay (normal: about 12 V with active control). For a complete diagnosis, use an OBD-II scanner.
Is it safe to drive with P0686?
Do not drive — repair immediately
How much does it cost to fix P0686?
The estimated repair cost for P0686 is $6–111. Actual cost depends on your vehicle, location, and labor rates.
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