P0684 Fault Code

Glow Plug Control Module to PCM Communication Circuit Range/Performance

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

The P0684 fault code indicates an issue with the communication between the Glow Plug Control Module and the Powertrain Control Module (PCM). This communication is essential for the proper functioning of the glow plugs, which are used to preheat the engine air for better cold starting performance. When this code is triggered, it suggests that the signal between the two modules is either out of range or not performing as expected.

What are the symptoms of the P0684 code?

Symptoms that may be associated with the P0684 code include:

• Difficulty starting the engine, particularly in cold weather
• Increased engine crank time
• Poor fuel economy due to incomplete combustion
• Engine misfires or rough idle
• Dashboard warning lights illuminated, such as the Check Engine Light

What causes the P0684 code?

Common causes of the P0684 code include:

• Faulty Glow Plug Control Module
• Damaged wiring or connectors between the Glow Plug Control Module and the PCM
• Short circuits or open circuits in the communication lines
• A malfunctioning Powertrain Control Module
• Corrosion or water intrusion in the electrical connectors

How to fix P0684?

To resolve the P0684 fault code, consider the following steps:

1. Inspect and repair any damaged wiring or connectors between the Glow Plug Control Module and the PCM.
2. Test the Glow Plug Control Module to ensure it is functioning correctly. Replace if necessary.
3. Check for any short or open circuits in the communication lines.
4. Perform a PCM software update if the module is functioning but not communicating properly.
5. Clear the fault code and conduct a test drive to see if the code returns.