What Does P0690 Mean?
The PCM has detected a high voltage condition on the ECM/PCM power relay sense circuit. The sense wire is reading higher voltage than expected, which may indicate the relay contacts are seeing a voltage spike, there is a short to a higher voltage source, or a feedback issue exists in the sense circuit. This can cause the PCM to incorrectly assess its own power supply stability.
Safety Warning
High voltage on the PCM power sense circuit can cause the PCM to enter protective shutdown or operate erratically. If caused by an overcharging alternator, the excess voltage can damage other electronic modules throughout the vehicle. Diagnose and repair promptly.
Common Causes
30%
Short to battery or ignition voltage in the sense wire
25%
Overcharging condition from alternator pushing system voltage too high
20%
ECM/PCM power relay with erratic contact behavior (arcing/bouncing)
15%
Corroded or improperly terminated sense wire at PCM connector
10%
Voltage spike from inductive load on shared circuit
Diagnostic Steps
1
Measure system voltage with the engine running; it should be 13.5-14.5V. Readings above 15V indicate an overcharging alternator or failed voltage regulator.
2
With the engine running, measure voltage at the PCM sense circuit input pin; compare to actual battery voltage. A higher reading indicates a short to another voltage source.
3
Check the sense wire routing for contact with other power wires that could backfeed a higher voltage into the circuit.
4
Inspect the relay contacts for signs of arcing or pitting by removing and visually examining the relay; degraded contacts can cause voltage spikes during operation.
5
Verify proper suppression diode function on the relay coil (if equipped); a failed diode can cause voltage spikes that feed back through the sense circuit.
Estimated Repair Cost
$50 - $550
Parts + labor, varies by vehicle and location
The PCM has detected a high voltage condition on the ECM/PCM power relay sense circuit. The sense wire is reading higher voltage than expected, which may indicate the relay contacts are seeing a voltage spike, there is a short to a higher voltage source, or a feedback issue exists in the sense circu...
The most common cause of P0690 (ECM/PCM Power Relay Sense Circuit High) is: Short to battery or ignition voltage in the sense wire
Typical repair costs for P0690 range from $50 to $550, depending on the vehicle, location, and whether you do it yourself or go to a shop.
High voltage on the PCM power sense circuit can cause the PCM to enter protective shutdown or operate erratically. If caused by an overcharging alternator, the excess voltage can damage other electronic modules throughout the vehicle. Diagnose and repair promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0690 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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