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, potentially causing intermittent or complete loss of power to the ECM/PCM.
01. Most Common Causes
- Faulty ECM/PCM power relay
- Corroded or damaged relay socket or wiring
- Blown fuse for ECM/PCM power relay
- Low battery voltage or poor battery connection
02. Symptoms You Will Notice
- Engine may not start or stalls
- Check Engine Light illuminated
- Intermittent electrical issues
- Reduced engine performance
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and note freeze frame data.
Step 2: Inspect the ECM/PCM power relay and its socket for corrosion or damage.
Step 3: Test the relay by swapping with a known good relay of the same type.
Step 4: Check the fuse for the ECM/PCM power relay and replace if blown.
Step 5: Measure voltage at the relay control and power circuits with a multimeter.
Step 6: Inspect wiring and connectors for breaks, shorts, or poor connections.
04. Commonly Affected Makes
05. 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 parts and labor, but costs can vary if the ECM/PCM itself needs replacement.