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 computer in the car found a problem with the little heater in the engine that helps it start when it's cold. It's like when a toaster doesn't heat up because there's a problem with the electrical plug.
The P066F code indicates that the engine control module (ECM) has detected a high voltage condition in the glow plug control circuit for cylinder 3.
The glow plug is a heating device used to aid in starting diesel engines. The ECM monitors the voltage and current in the glow plug circuit. If it detects a voltage that is higher than expected, it sets the P066F code. This could be due to a short to voltage, an open circuit, or a faulty glow plug.
• Hard starting when the engine is cold
• Engine misfire
• Check Engine Light illuminated
• Faulty glow plug for cylinder 3
• Open or shorted glow plug circuit
• Faulty glow plug control module
• Corroded or damaged connectors or wiring
Glow Plug: A device used to heat the air in a diesel engine to help it start.
ECM: Engine Control Module, the computer that controls the engine's functions.
• Use an OBD-II scanner to confirm the code.
• Inspect the glow plug and its wiring for damage or corrosion.
• Test the glow plug control module for proper operation.
• Replace the faulty glow plug.
• Repair or replace damaged wiring or connectors.
• Replace the glow plug control module if necessary.
• OBD-II scanner
• Multimeter
• Socket set
$100 - $300
Moderate
• Ford F-250
• Chevrolet Silverado
• Dodge Ram 2500
• Regularly inspect glow plugs and wiring.
• Ensure proper maintenance of the electrical system.
• Use high-quality glow plugs.
Sensor Issue
• Have a professional inspect the glow plug system.
• Avoid using the vehicle in very cold conditions until repaired.
Check with the vehicle manufacturer, as glow plugs may be covered under powertrain warranty.
Glow plug issues are common in diesel engines, especially in colder climates where they are used frequently.
Moderate – It should be addressed soon to avoid starting issues.
Ignoring this issue may lead to starting difficulties and potential engine damage.
• Engine must be cold to test the glow plug system.
• Ensure the battery is fully charged.
The glow plug for cylinder 3 is located on the engine block, typically near the top of the cylinder head.
Q: Can I drive with a P066F code?
A: It's possible to drive, but you may experience hard starting and engine misfires, especially in cold weather.
Q: How do I know if a glow plug is bad?
A: Symptoms include hard starting, engine misfire, and a check engine light. A multimeter can be used to test the glow plug's resistance.
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Fitment Required · Vehicle-fitment part
Commonly relevant for misfire, ignition-efficiency, and some drivability-related repairs.
Misfire and ignition-related faults commonly involve spark plugs as part of the repair path.
Check the correct plug type, gap, and engine application for your vehicle.
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Fitment Required · Vehicle-fitment part
Relevant when the fault points toward ignition-coil performance or cylinder-specific ignition issues.
Some ignition faults involve coil performance or cylinder-specific coil problems.
Match the coil to your engine and confirm the failed component before ordering.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.