P0688 Fault Code

ECM/PCM Power Relay Sense Circuit

• What does that mean?
• Symptoms
• Causes
• Solutions

The P0688 fault code indicates an issue with the ECM/PCM power relay sense circuit. This circuit is responsible for ensuring the engine control module (ECM) or powertrain control module (PCM) receives proper voltage to function effectively. If the relay sense circuit detects an abnormal condition, it triggers the P0688 code, which may lead to various performance issues in the vehicle.

What are the symptoms of the P0688 code?

When the P0688 code is present, you may observe:

• The engine may fail to start or have difficulty starting.
• The vehicle may experience stalling or erratic engine behavior.
• There may be warning lights illuminated on the dashboard, primarily the check engine light.
• The vehicle's performance may degrade, leading to reduced power or acceleration.

What causes the P0688 code?

Several factors can cause the P0688 fault code, including:

• A faulty ECM/PCM power relay that is not functioning properly.
• Wiring issues or shorts in the relay sense circuit.
• Poor connections or corroded terminals that disrupt the electrical flow.
• A malfunctioning ECM or PCM that cannot correctly interpret the signals received from the relay.

How to fix P0688?

To resolve the P0688 fault code, follow these steps:

1. Begin by using a scanner to verify the code and perform a visual inspection of the ECM/PCM power relay.
2. Check the relay for proper operation and replace it if defective.
3. Inspect the wiring and connectors in the relay sense circuit for any signs of damage or corrosion, repairing as needed.
4. Test the ECM/PCM to ensure it is functioning correctly and replace it if necessary.
5. Clear the fault codes and conduct a road test to confirm that the issue is resolved.