OBD-II Error Code P0687: How to Fix It (ECM/PCM Power Relay Control Circuit High)

Medium 30-60 minutes Medium Severity Verified June 2026
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Error Code
P0687
Brand
OBD-II Generic
Product Type
automotive
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes
Error code P0687 means your vehicle's engine control module (ECM) or powertrain control module (PCM) has detected a high voltage signal in the power relay control circuit. This usually points to a faulty relay, wiring issue, or a failing ECM/PCM. It can cause starting problems or unexpected stalling.
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Tools You'll Need

How to Fix Error Code P0687

  1. Check for Safety and Gather Tools

    Always disconnect the battery before working on electrical components to avoid shock or short circuits.

  2. Locate the ECM/PCM Power Relay

  3. Test the Power Relay

    Do not apply 12V to the relay coil for more than a few seconds; prolonged power can damage it.

  4. Inspect the Relay Wiring and Connectors

    Be careful not to short any pins while probing with the ignition on.

  5. Test the ECM/PCM Control Output

    Only attempt this if you are comfortable working with sensitive electronics. Static discharge can damage the ECM.

  6. Replace the ECM/PCM if Necessary (Last Resort)

    Replacing the ECM without proper programming may prevent the car from starting.

Parts You May Need

ECM/PCM Power Relay
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ECM/PCM Power Relay
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ECM/PCM Power Relay
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ECM/PCM Power Relay
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When to Call a Professional

If after testing the relay and wiring, the problem persists, or if you suspect a faulty ECM/PCM, call a professional mechanic. ECM replacement requires specialized programming tools. Also seek help if you're uncomfortable working with electrical systems.

Frequently Asked Questions

What does OBD-II error code P0687 mean?
P0687 indicates a high voltage condition in the ECM/PCM power relay control circuit. This relay supplies power to the engine computer. A high signal can prevent the computer from turning on or staying on, leading to no-start or stalling.
Can I drive with a P0687 code?
Not recommended. The code may cause the engine to stall or not start at all. Driving could leave you stranded or cause further electrical damage. Fix the issue promptly.
How much does it cost to fix code P0687?
If it's just a relay, the part costs $10-$30. Labor varies. A mechanic may charge $100-$200 for diagnosis and replacement. If the ECM needs replacement, costs can be $500-$1000 or more including programming.
What causes code P0687?
Common causes: faulty ECM/PCM power relay, corroded or damaged wiring, loose connectors, or a failing ECM/PCM. Water intrusion in the fuse box can also cause issues.
Is P0687 the same as P0686?
No. P0686 indicates a low voltage condition in the same circuit, while P0687 is high voltage. Both relate to the power relay control circuit but have opposite faults.

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