P0681
UniversalECM/PCM Power Relay Sense Circuit/Open
High SeverityThis code indicates an electrical issue where the Powertrain Control Module (PCM) or Engine Control Module (ECM) is not receiving the expected feedback signal from its main power relay, suggesting an open circuit. This can lead to the engine computer not powering up correctly, resulting in a no-start condition, unexpected stalling, or various other drivability problems.
⚠️ Before You Begin (Safety First)
Electrical system diagnostics can be dangerous. Always disconnect the battery before inspecting or working on electrical components to prevent electrical shock or damage to the vehicle's computer systems. Ensure the engine is cool before working near engine components.
Common Symptoms
- Check Engine Light illuminated
- Engine cranks but does not start
- Engine stalls unexpectedly while driving
- Intermittent loss of engine power
- Vehicle may not start at all
- Various other electrical system malfunctions
Common Causes
- Faulty ECM/PCM power relay
- Open circuit or high resistance in the ECM/PCM power relay sense circuit wiring
- Corroded, loose, or damaged electrical connectors for the relay or ECM/PCM
- Blown fuse associated with the ECM/PCM power supply
- Faulty ECM/PCM (less common, but possible)
Frequently reported on: All Makes
Diagnostic Steps
- Visually inspect all fuses related to the ECM/PCM and the main power relay. Replace any blown fuses.
- Locate the ECM/PCM power relay and visually inspect it and its connector for signs of damage, corrosion, or loose terminals.
- Using a digital multimeter, test the ECM/PCM power relay for proper operation according to your vehicle's service manual, or temporarily swap it with a known good, identical relay from a non-critical circuit if available.
- Access vehicle-specific wiring diagrams and use a multimeter to test for continuity and proper voltage signals along the ECM/PCM power relay sense circuit, checking for any open circuits or excessive resistance.
- Carefully inspect the entire wiring harness for the ECM/PCM power relay circuit for any signs of chafing, pinching, or damage, especially where it passes through firewalls or near moving engine parts.
👨🔧 When to Call a Professional
If you lack experience with automotive electrical diagnostics, particularly using a multimeter to test voltage, continuity, and circuit integrity, it is best to consult a professional mechanic. Incorrect diagnosis or repair can lead to further damage to the ECM/PCM or other electrical components.
Commonly Asked Questions
Can I drive my car with a P0681 code?
Driving with a P0681 code is not recommended as it indicates an issue with the main computer's power supply. This can lead to unexpected engine stalling or a no-start condition, making the vehicle unreliable and potentially unsafe.
What is the most common cause of a P0681 code?
The most common causes for a P0681 code are a faulty ECM/PCM power relay, a blown fuse in the power circuit, or an open circuit in the wiring related to the relay's sense circuit.
How can I test the ECM/PCM power relay?
You can test the relay using a multimeter to check for continuity and proper switching when power is applied to its control terminals. Alternatively, you can temporarily swap it with a known good, identical relay from another non-critical circuit in your vehicle.
Does a P0681 code always mean my ECM/PCM is bad?
Not necessarily. While a faulty ECM/PCM can sometimes be the cause, it is typically one of the last components to consider after thoroughly ruling out issues with the power relay, associated fuses, and the wiring harness.
Will clearing the P0681 code fix the problem?
Clearing the code will only turn off the Check Engine Light temporarily. The underlying electrical issue must be diagnosed and repaired for the code to stay off and for the vehicle to function correctly and reliably.