ECM/PCM Power Relay Sense Circuit Low
The P0689 code indicates that the Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected a low voltage condition on the power relay sense circuit. This circuit monitors the voltage output from the ECM/PCM power relay to ensure the control module is receiving proper power. A low voltage reading suggests a problem with the relay, wiring, or the control module itself, which can lead to intermittent or complete loss of engine control.
1. Most Common Causes
- Faulty ECM/PCM power relay
- Corroded or damaged relay socket or wiring
- Blown fuse for the ECM/PCM relay circuit
- Low battery voltage or poor battery connections
- Faulty ECM/PCM (rare)
2. Symptoms You Will Notice
- Engine may not start or stalls unexpectedly
- Check Engine Light illuminated
- Intermittent electrical issues (e.g., gauges flickering)
- Reduced engine performance or limp mode
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and document freeze frame data.
Step 2: Inspect the ECM/PCM power relay and its socket for corrosion, damage, or loose connections.
Step 3: Check the relay fuse and battery voltage (should be 12.6V or higher).
Step 4: Test the relay by swapping with a known good relay of the same type.
Step 5: If relay is good, check for voltage at the relay control and output terminals using a multimeter.
Step 6: Inspect wiring and connectors between the relay and ECM/PCM for opens or shorts.
Step 7: If all else fails, test the ECM/PCM for internal faults (requires professional scan tool).
4. Frequently Asked Questions
Is it safe to drive with this code?▼
No, it is not safe. The vehicle may stall or fail to start, leading to a dangerous situation. Have it diagnosed and repaired promptly.
How much does it cost to fix?▼
Typically $50-$150 for relay replacement and basic wiring repair. If the ECM/PCM needs replacement, costs can exceed $500.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.