P0689
UniversalECM/PCM Power Relay Sense Circuit Low
High SeverityThis code indicates that the Powertrain Control Module (PCM) or Engine Control Module (ECM) detected a low voltage condition in the circuit that monitors its main power supply relay. This can prevent the ECM/PCM from receiving consistent power, leading to engine performance issues or a no-start condition.
⚠️ Before You Begin (Safety First)
Always disconnect the battery before performing any electrical work on your vehicle to prevent accidental shorts or injury. Ensure the engine is cool before working on any components that might be hot.
Common Symptoms
- Engine cranks but does not start
- Engine stalls unexpectedly
- Intermittent engine misfires or rough running
- Check Engine Light illuminated
- Vehicle will not start at all
Common Causes
- Faulty ECM/PCM power relay
- Corroded, loose, or damaged wiring in the relay control circuit or power supply circuit to the PCM/ECM
- Blown fuse for the ECM/PCM power relay
- Faulty PCM/ECM (less common)
- Poor ground connection for the PCM/ECM
Frequently reported on: General/Universal
Diagnostic Steps
- Using an OBD-II scanner, confirm P0689 is the only code present.
- Locate the ECM/PCM power relay and its associated fuse(s) in your vehicle's fuse box (consult your owner's manual).
- Visually inspect the relay and fuse for any signs of damage, corrosion, or a blown filament.
- Test the ECM/PCM power relay by swapping it with a known good, identical relay from another non-critical system (e.g., horn relay), or by using a multimeter to check its functionality.
- With the battery disconnected, carefully inspect the wiring harness and connectors leading to the ECM/PCM power relay and the PCM/ECM for any signs of fraying, corrosion, or looseness.
- Use a multimeter to check for proper voltage at the relay socket and for continuity in the relevant wires, as per your vehicle's wiring diagrams.
👨🔧 When to Call a Professional
If you have checked the ECM/PCM power relay and associated fuses, and the issue persists or if you are uncomfortable diagnosing complex electrical circuits, it is best to consult a professional mechanic. Improper electrical diagnosis can lead to further damage to vehicle systems.
Commonly Asked Questions
Can I drive with a P0689 code?
It is not recommended to drive with a P0689 code. This issue can lead to unexpected engine stalling or a no-start condition, which can be dangerous and leave you stranded.
Where is the ECM/PCM power relay located?
The location of the ECM/PCM power relay varies by vehicle make and model. It is typically found in the under-hood fuse box or a dedicated relay center. Refer to your vehicle's owner's manual or a service manual for its exact location.
Is a P0689 code always caused by a bad relay?
While a faulty relay is a common cause, the P0689 code can also be triggered by a blown fuse, corroded or damaged wiring in the relay's circuit, poor ground connections, or, in rare cases, an internal fault within the PCM/ECM itself. Thorough diagnosis is key.
How can I test the ECM/PCM power relay?
You can test the relay by carefully swapping it with a known good, identical relay from a less critical circuit (like the horn or fog lights). If the problem resolves, the original relay was likely at fault. You can also use a multimeter to test for continuity and proper operation according to your vehicle's service manual.