The P0690 code is a generic OBD-II diagnostic trouble code indicating “ECM/PCM Power Relay Sense Circuit High.” It means the powertrain control module detected excessive voltage in its main power relay sense circuit when the relay should be off.
This code does not automatically prove the relay or control module has failed. Diagnosis requires testing the main power fuses, the relay control circuit, and the ignition switch feeds before replacing components.
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Key Takeaways
- The P0690 code indicates the control module detected a high voltage condition in the ECM/PCM power relay sense circuit.
- Possible causes include a failed main power relay, a short to voltage in the sense wiring, or an internal control module fault.
- Diagnosis involves checking the main PCM fuses, testing the power relay, and verifying the ignition switch feeds.
- Repairs may involve replacing the relay, repairing the wiring harness, or replacing the control module if internal faults are confirmed.
P0690 Code Description and Implications
The P0690 code indicates that the powertrain control module detected a high voltage state in the ECM/PCM power relay sense circuit. This generic category of trouble codes applies to most OBD-II equipped vehicles.
The main power relay supplies battery voltage to the control module when the ignition is turned on. The module monitors a dedicated sense circuit to verify that the relay is functioning correctly and cutting power when the ignition is off.
When the module detects voltage on this sense circuit while the relay is commanded off, it stores this code. This electrical fault can prevent the module from entering sleep mode or cause a no-start condition.
Common Causes of the P0690 Code
A short to voltage in the wiring harness between the PCM power relay and the control module sense pin is a primary cause. This can occur if the wire chafes against another powered circuit.
A mechanically stuck or internally shorted main PCM power relay can continuously feed voltage to the control module, even when the ignition switch is turned off.
An internally failed powertrain control module can misinterpret the voltage signal on the sense circuit, though this is less common than external wiring or relay faults.
Symptoms Associated With P0690
An illuminated Check Engine Light is expected once the monitor detects the circuit fault. MIL behavior varies by application, but the light commands when the electrical fault is verified.
You may experience a no-start condition or a no-crank event if the main power relay fails to engage or if the control module does not receive the proper wake-up signals.
In some applications, the vehicle may experience battery drain because the control module remains powered on after the ignition is switched off, preventing the system from entering sleep mode.
Diagnosing the P0690 Trouble Code
Diagnosis must begin by confirming the exact factory definition and checking for related communication or power supply codes. Record freeze-frame data to see the ignition and voltage states when the code set.
Locate and test the main PCM power relay and its associated fuses in the underhood fuse block. Verify that the relay clicks and that battery voltage is present at the supply pins.
Inspect the wiring harness between the relay and the control module. Use a multimeter to test the sense circuit for a short to voltage or continuity issues.
If the relay and wiring test correctly, the fault may lie within the control module itself, requiring module-level diagnosis according to the exact service information.
Repairing the P0690 Issue
Repairs must follow confirmed diagnosis. If the wiring harness is found to be shorted to another voltage source, repair the circuit and secure the harness away from sharp edges.
If electrical testing confirms the main PCM power relay is internally shorted or mechanically jammed, replace the relay using a component meeting the exact vehicle specification.
If the manufacturer diagnostic procedure confirms the control module as the fault, follow the applicable module service or replacement procedure, which may require programming.
Cost Considerations for P0690 Repairs
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Replacing a standard underhood relay or repairing a localized wiring short involves minimal parts and moderate labor expenses.
If the powertrain control module requires replacement and programming, the cost of the component and the required software configuration will dictate the overall repair price.
Prevention Strategies for Future Occurrences
Inspecting the underhood fuse box and relay center for moisture intrusion or corrosion during routine maintenance can help prevent electrical faults in the main power supply circuits.
Ensuring that aftermarket accessories are wired correctly and do not backfeed voltage into the ignition or PCM sense circuits helps prevent false circuit high codes.
Some electrical component failures occur due to normal aging and cannot be reliably prevented.
Troubleshooting Tips and Best Practices
Do not attempt to fix a P0690 code by simply replacing the powertrain control module without checking the main power relay and ignition switch feeds first. External wiring faults are a frequent cause.
Always verify the exact location of the PCM power relay. On many applications, it is located in the main underhood fuse block and may be labeled as the ECM, PCM, or Main relay.
Check for technical service bulletins for your exact vehicle application, as some manufacturers release updated relay designs or revised wiring harness pigtails to address chronic power sense faults.
More OBD-II Codes
| P0688 | P0685 | P0606 | P0605 |
| P0604 | P0603 | P0602 | P0601 |
| P0600 | P0607 | U0100 | U0101 |
| U0107 | P0700 | P0641 | P0651 |
| P0652 | P0654 | P0650 | P0657 |
| P0638 | P0633 | P0625 | P0620 |
Frequently Asked Questions
Is the P0690 code generic or manufacturer-specific?
Yes, P0690 is a generic SAE OBD-II diagnostic trouble code. However, the exact power relay circuit architecture and testing procedures vary by manufacturer and vehicle application.
Will a P0690 code cause a no-start condition?
It can. The main PCM power relay supplies voltage to the control module. If the relay or sense circuit fails, the module may not receive power or wake-up signals, preventing the engine from starting.
Does a P0690 code mean my PCM is broken?
Not necessarily. While internal module faults can occur, this code is frequently caused by a shorted wire, a failed main power relay, or a blown fuse. Proper electrical testing is required first.
Can a bad ignition switch cause a P0690 code?
Yes. The ignition switch commands the main power relay. If the switch fails and backfeeds voltage or fails to trigger the relay correctly, it can cause faults in the PCM power sense circuit.
Can I clear the P0690 code without fixing the problem?
Clearing the code only resets the warning light. If the underlying wiring short, failed relay, or module issue remains, the monitor will detect the high voltage condition immediately and turn the light back on.
What Should You Do About the P0690 Code?
Confirm the exact factory definition and check for related power supply codes for your specific vehicle application. Follow the applicable manufacturer diagnostic procedure to verify whether the fault lies in the main power relay, the wiring harness, or the control module itself.
Once testing confirms the root cause, repair or replace the confirmed failed component in the relevant system, then retest the ignition power cycles to ensure the control module wakes and sleeps correctly.
