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DTC codes / P06xx · Computer and output circuits / P067C

P067CCylinder 5 Glow Plug Control Circuit Low

P067C means the engine computer has detected a low-voltage condition on the control circuit for cylinder 5's glow plug, which is used to heat the combustion chamber for cold starts in diesel engines. The computer monitors the circuit and sets this code when the voltage on the control side is lower than expected, indicating a short to ground, a failed glow plug, or a wiring problem.

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

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Hard starting or rough idle when the engine is cold
  • Excessive white smoke from the exhaust after a cold start
  • Engine misfire or stumbling during the first few minutes of operation
  • Reduced fuel economy during cold-weather driving

Common causes, most likely first

  1. Failed glow plug on cylinder 5 (open or shorted internally)
  2. Damaged or corroded electrical connector at the cylinder 5 glow plug
  3. Chafed, broken, or shorted wire in the glow plug control circuit
  4. Faulty glow plug control module (GPCM) or relay
  5. Poor ground connection for the glow plug circuit
  6. Engine control module (ECM) internal driver fault (rare)

How to diagnose and fix it

  1. Scan all modules for stored codes and freeze-frame data to confirm P067C is active and not historical.
  2. Visually inspect the cylinder 5 glow plug connector and wiring for corrosion, looseness, or damage.
  3. Measure the resistance of the cylinder 5 glow plug with a multimeter and compare it to the manufacturer's specification.
  4. Check the control circuit for a short to ground by disconnecting the glow plug and testing the wire from the control module.
  5. Test the glow plug control module or relay operation, including power and ground feeds, using a wiring diagram.
  6. If the glow plug is faulty, replace it and clear the code; if the circuit is shorted, repair the wiring harness.
  7. After repairs, clear codes and perform a cold-start test to verify the glow plug system operates correctly and the code does not return.

Glow plug circuit low: what techs check first

  • A low-voltage code on a glow plug circuit often results from a short to ground in the harness rather than a failed glow plug itself, so always inspect the wiring before replacing parts.
  • The glow plug control module may set this code if it detects excessive current draw from a shorted glow plug, but a faulty module can also mimic a circuit fault, so test the module's output signal.
  • On some vehicles, a weak battery or poor charging system can cause low voltage on the glow plug circuit and trigger this code, so verify battery condition and connections.
  • P067C is specific to cylinder 5, but a single failed glow plug can cause the entire glow plug system to shut down on certain models, leading to multiple glow plug codes.
  • Do not overlook the ground path for the glow plug circuit; a corroded ground strap can create a low-voltage condition that sets this code without any faulty component.

Can I keep driving with P067C?

You can usually drive with P067C, but cold starting may be difficult and the engine may run rough until warm. Avoid heavy loads or long idling until the fault is repaired, and address it promptly to prevent further glow plug system damage.

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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