What are the common causes of P0686?

A weak or failing power relay. A short to ground in the control circuit. A corroded relay connector. Low battery voltage. A faulty ECM driver.

Read the relay control voltage on a scan tool. Check the control circuit for a short to ground. Test the relay coil and contacts. Verify battery voltage and charging. Replace the relay or repair the circuit. Clear the code and retest.

P0686

ECM/PCM Power Relay Control Circuit Low

System: Computer output circuits (P code)
Lamp: Check Engine Light
Category: Powertrain - Computer and Auxiliary Controls

What it means

P0686 means ECM/PCM Power Relay Control Circuit Low.

Where it lives

For P0686, the circuit described runs through the relay. The description of P0686 reports a fault at the relay.

Check these first

A weak or failing power relay
A short to ground in the control circuit
A corroded relay connector
Low battery voltage
A faulty ECM driver

What to do next

Read the relay control voltage on a scan tool
Check the control circuit for a short to ground
Test the relay coil and contacts
Verify battery voltage and charging
Replace the relay or repair the circuit
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.