P0686 Fault Code

ECM/PCM Power Relay Control Circuit Low

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

The P0686 fault code indicates a problem with the ECM (Engine Control Module) or PCM (Powertrain Control Module) power relay control circuit. This code signals that the power relay is not functioning correctly, which can affect engine performance and electrical systems in the vehicle.

• The ECM/PCM relies on a stable power supply to operate effectively.
• A low voltage signal detected in the power relay circuit can cause performance issues or prevent the engine from starting.

What are the symptoms of the P0686 code?

When the P0686 code is present, you may notice:

• The engine may not start or have difficulty starting.
• Electrical components may exhibit erratic behavior due to fluctuations in power.
• Potentially poor engine performance, including stalling or rough idling.
• Dashboard warning lights, particularly Check Engine Light, may be activated.

What causes the P0686 code?

Several factors can lead to the P0686 code being triggered:

• A faulty ECM or PCM that cannot regulate power correctly.
• Damaged wiring or connectors in the power relay circuit.
• A malfunctioning power relay that fails to supply adequate voltage.
• Blown fuses that disrupt the power flow to the ECM/PCM.

How to fix P0686?

To resolve the P0686 fault code, follow these steps:

• Inspect the wiring and connectors for any signs of damage or corrosion.
• Test the power relay to ensure it is functioning correctly, and replace it if necessary.
• Check related fuses for continuity and replace any blown fuses.
• Use a diagnostic scanner to clear the code and test drive the vehicle to ensure the issue is resolved. If the code reappears, further diagnosis of the ECM/PCM may be required.