• Difficulty starting the engine
• Check Engine Light illuminated
• Reduced engine performance
• Faulty Glow Plug Control Module
• Open or shorted CAN bus wiring
• Faulty ECU or software issue
ECU: Engine Control Unit
CAN bus: Controller Area Network bus, a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer
• U0100
• U0101
This code means that the car's computer isn't able to talk to the glow plug control module, which helps the engine start, especially when it's cold.
U0686 indicates a communication failure with the Glow Plug Control Module.
The U0686 code is set when the vehicle's main computer (ECU) cannot communicate with the Glow Plug Control Module over the CAN bus network. This communication is essential for coordinating the operation of the glow plugs, which are used to heat the engine cylinders in diesel engines for easier starting.
• Check for other codes and address them first.
• Inspect CAN bus wiring for damage or disconnection.
• Test the Glow Plug Control Module for faults.
• Repair or replace damaged wiring.
• Replace the Glow Plug Control Module if faulty.
• Reprogram or update ECU software if needed.
• OBD-II scanner
• Multimeter
• Wiring diagram
$150 - $500
Moderate
• Ford F-250
• Chevrolet Silverado 2500
• Ram 2500
• Regularly inspect wiring for damage.
• Ensure software updates are performed.
• Keep the engine and electrical components clean.
Communication Error
• Avoid driving long distances until the issue is resolved.
• Consult with a professional mechanic for accurate diagnostics.
Check with the vehicle manufacturer for warranty coverage on electrical components.
This code has been more common in diesel vehicles due to their reliance on glow plugs for starting.
Moderate – It can affect starting and engine performance, but immediate repair is not critical unless symptoms worsen.
Driving with this code may lead to starting issues, which could be inconvenient or unsafe in certain situations.
• Engine off
• Key in the ON position
The Glow Plug Control Module is typically located near the engine or attached to the engine block.
Q: Can I drive with a U0686 code?
A: It's possible, but you may experience starting issues, especially in cold weather.
Q: How can I reset the U0686 code?
A: Fix the underlying issue and then use an OBD-II scanner to clear the code.
