P0688 - ECM/PCM Power Relay Sense Circuit/Open

The ECM detected an open or fault in the ECM/PCM power relay sense circuit.

Code Overview

The ECM detected an open or fault in the ECM/PCM power relay sense circuit.

Common Causes

• Relay, module, sensor, or control-circuit fault
• Damaged wiring or connector
• Power-supply or ground issue

Diagnostic Steps

1. Inspect related relay, connector, and harness condition
2. Check power, ground, and control signal where applicable
3. Review companion codes before replacing parts

Likely Repairs & Cost Guides

Use test results to confirm the fault before pricing the repair.

Related OBD Codes

Browse the closest code-family pages when the same fault pattern often shows up nearby.

Next Steps

Move from the code to a diagnosis path, then into repair pricing once the fault is confirmed.