What Does P0687 Mean?
The PCM has detected a high voltage condition on the ECM/PCM power relay control circuit. This indicates the control wire is being held at a higher voltage than expected, which could be due to an open ground on the relay coil or a short to battery voltage in the control circuit. The relay may not function properly, causing intermittent power loss to the PCM.
Safety Warning
This is a safety concern. An improperly functioning PCM power relay can cause sudden engine shutdown while driving, resulting in loss of power steering and reduced braking. The vehicle should be diagnosed and repaired before normal driving, especially on highways.
Common Causes
30%
Open ground circuit for the ECM/PCM power relay coil
25%
Short to battery voltage in the relay control circuit
20%
Failed ECM/PCM power relay with open ground side
15%
Corroded or loose ground connection in relay circuit
10%
PCM relay driver circuit stuck high
Diagnostic Steps
1
With the relay removed, check the relay coil ground circuit for continuity to chassis ground; an open ground will cause a high voltage reading on the control side.
2
Measure the relay coil resistance to verify the relay itself is not open internally (should be 60-100 ohms).
3
Inspect the relay control circuit wiring for any contact with battery voltage sources; the wire may be chafed against a power feed wire in the harness.
4
Verify all ground connections in the fuse box and relay panel area are clean and tight, with less than 0.1 ohm resistance to the battery negative terminal.
5
Substitute a known-good relay and retest; if the code clears, the original relay's internal ground path was the issue.
Estimated Repair Cost
$50 - $500
Parts + labor, varies by vehicle and location
The PCM has detected a high voltage condition on the ECM/PCM power relay control circuit. This indicates the control wire is being held at a higher voltage than expected, which could be due to an open ground on the relay coil or a short to battery voltage in the control circuit. The relay may not fu...
The most common cause of P0687 (ECM/PCM Power Relay Control Circuit High) is: Open ground circuit for the ECM/PCM power relay coil
Typical repair costs for P0687 range from $50 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This is a safety concern. An improperly functioning PCM power relay can cause sudden engine shutdown while driving, resulting in loss of power steering and reduced braking. The vehicle should be diagnosed and repaired before normal driving, especially on highways.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0687 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Control Module Power Supply
Difficulty
Type
Generic (SAE)
Recommended Tools
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