What Does P064C Mean?
The glow plug control module (GPCM) has an internal malfunction or communication error. This code applies to diesel engines and indicates the ECM cannot properly communicate with or detect proper operation of the module that controls glow plug activation for cold starting. The driver may experience hard starting in cold weather, excessive white smoke on startup, or rough idle until the engine warms up.
Common Causes
35%
Failed glow plug control module (internal relay or driver circuit failure)
25%
Corroded or damaged wiring/connector at the GPCM
20%
Loss of power supply or ground to the glow plug control module
15%
CAN bus communication fault between ECM and GPCM
5%
Low battery voltage causing GPCM malfunction (glow plugs draw very high current)
Diagnostic Steps
1
Check for additional glow plug codes (P0380-P0384, P067x) and communication codes (U-codes). Verify battery voltage is at least 12.4V — glow plug systems are very sensitive to low voltage.
2
Locate the glow plug control module (typically on or near the engine valve cover). Inspect the connector for corrosion, melted pins, or heat damage — these modules handle very high currents.
3
Measure B+ at the GPCM power input (should be within 0.2V of battery voltage under load) and ground resistance (must be less than 0.1 ohms due to high current requirements).
4
Using a scan tool, attempt to communicate with the GPCM and command glow plug activation. Monitor individual glow plug current draw if the scan tool supports it.
5
With a clamp-on ammeter on the GPCM power feed, activate the glow plugs and verify total current draw matches specification (typically 8-15A per glow plug). Uneven or absent current draw confirms module failure.
Estimated Repair Cost
$200 - $800
Parts + labor, varies by vehicle and location
The glow plug control module (GPCM) has an internal malfunction or communication error. This code applies to diesel engines and indicates the ECM cannot properly communicate with or detect proper operation of the module that controls glow plug activation for cold starting. The driver may experience ...
The most common cause of P064C (Glow Plug Control Module) is: Failed glow plug control module (internal relay or driver circuit failure)
Typical repair costs for P064C range from $200 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle is drivable once started, but cold starting will be very difficult or impossible in cold weather. Prolonged cranking can damage the starter motor and drain the battery. Avoid driving in situations where you might need to restart a cold engine in freezing conditions until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P064C to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Glow Plug System
Difficulty
Type
Generic (SAE)
Recommended Tools
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