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DTC codes / P06xx · Computer and output circuits / P064C

P064CGlow Plug Control Module 1

P064C indicates that the powertrain control module (PCM) has detected a fault within the glow plug control module, which is the electronic unit responsible for cycling the glow plugs on diesel engines. The PCM monitors the control module's communication and electrical performance, and when the expected signals or voltage levels fall outside the programmed range, it stores this code and illuminates the check engine light.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light or service engine soon light
  • Hard starting or extended cranking when the engine is cold
  • Rough idle or misfire immediately after a cold start
  • White smoke from the exhaust during cold running
  • Often no symptoms besides the warning light, especially in mild weather

Common causes, most likely first

  1. Faulty glow plug control module
  2. Damaged or corroded wiring or connectors between the PCM and the glow plug control module
  3. Blown fuse or poor ground connection for the glow plug control module circuit
  4. Failed glow plug causing excessive current draw that stresses the control module
  5. PCM software issue or internal PCM fault
  6. Water intrusion or corrosion inside the glow plug control module housing

How to diagnose and fix it

  1. Scan all modules for related codes and record freeze-frame data to understand when the fault occurs
  2. Inspect the glow plug control module fuse and relay, and check for power and ground at the module connector
  3. Visually inspect the wiring harness and connectors between the PCM and the glow plug control module for chafing, corrosion, or loose pins
  4. Test the glow plugs for resistance and compare to specifications to rule out a failed plug that may have damaged the module
  5. Perform a voltage drop test on the control module ground circuit and repair any excessive resistance
  6. If all external circuits test good, substitute a known-good glow plug control module and clear the code to see if it returns
  7. Verify the repair by clearing codes, performing a cold-start test, and confirming the monitor runs without resetting the code

What the glow plug module code hides

  • A failed glow plug can draw excessive current and damage the control module, so always test the plugs before replacing the module to avoid a repeat failure.
  • Corroded or loose ground connections at the module are a frequent cause that is often overlooked because the module itself tests fine on a bench.
  • The code can set intermittently due to a wiring harness rubbed through near the engine block, so a wiggle test while monitoring live data is essential.
  • On some vehicles, a weak battery or charging system fault can cause the module to log this code because low voltage disrupts its operation.
  • The PCM may set P064C even when the glow plug system is functioning, if communication on the control circuit is briefly interrupted by electrical noise from other components.

Can I keep driving with P064C?

You can usually drive the vehicle, but cold starting may be difficult and prolonged cranking can wear the starter and battery. Avoid heavy loads or long trips until the fault is repaired, and do not rely on the glow plugs for cold starts in freezing conditions.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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