Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the car's computer and the glow plug controller aren't talking to each other properly, which can make it hard for the engine to start, especially when it's cold.
The P0684 code indicates a communication issue between the Glow Plug Control Module (GPCM) and the Powertrain Control Module (PCM). This can affect the glow plug operation, crucial for starting diesel engines in cold conditions.
The Glow Plug Control Module is responsible for managing the glow plugs, which preheat the combustion chamber in diesel engines to ensure smooth starting. The PCM monitors the GPCM's performance. If the communication between these two modules is outside the expected range, the P0684 code is triggered.
• Difficulty starting the engine, especially in cold weather
• Check Engine Light is on
• Rough engine idle
• Faulty Glow Plug Control Module
• Wiring issues between GPCM and PCM
• Faulty PCM
PCM: Powertrain Control Module
GPCM: Glow Plug Control Module
• Scan for codes and freeze frame data
• Inspect wiring and connectors between GPCM and PCM
• Test the Glow Plug Control Module
• Repair or replace damaged wiring/connectors
• Replace the Glow Plug Control Module
• Replace the PCM if necessary
• OBD-II scanner
• Multimeter
• Wiring diagram
$150 - $600
Moderate
• Ford F-250
• Chevrolet Silverado 2500
• Dodge Ram 2500
• Regularly inspect and maintain wiring and connectors
• Ensure glow plugs are in good condition
• Keep the engine control modules updated
Communication Issue
• Have the vehicle inspected by a professional if the Check Engine Light is on
• Avoid starting the engine repeatedly in cold conditions if experiencing starting issues
Check with the vehicle manufacturer for warranty coverage on engine control components.
This code has been more prevalent in diesel engines due to their reliance on glow plugs for cold starts.
Moderate – While the vehicle may still operate, starting issues can worsen, especially in cold weather.
Ignoring this code can lead to starting difficulties, which may result in being stranded in cold conditions.
• Cold engine start
• Normal operating conditions
The Glow Plug Control Module is typically located in the engine compartment, near the engine block.
Q: What happens if I ignore this code?
A: Ignoring this code can lead to increased difficulty starting the engine, especially in cold weather, and may eventually prevent the engine from starting at all.
Q: Can I drive with this code?
A: You may be able to drive, but it's not recommended, especially in cold weather, as starting issues could leave you stranded.
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