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DTC codes / P06xx · Computer and output circuits / P06C9

P06C9Cylinder 5 Glow Plug Incorrect

P06C9 indicates that the engine control module has detected an incorrect electrical condition in the glow plug circuit for cylinder 5, typically an open circuit, short to ground, or short to power. The module compares expected glow plug current draw against actual feedback and sets this code when the values fall outside the programmed threshold for that cylinder.

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

Symptoms you may notice

  • Illuminated check engine light or glow plug warning lamp, often with no other symptoms
  • Hard cold starting or extended cranking before the engine fires
  • Rough idle and white smoke from the exhaust immediately after a cold start
  • Misfire-like shudder or hesitation until the engine reaches operating temperature
  • Increased fuel consumption during warm-up and the first few minutes of driving

Common causes, most likely first

  1. Failed glow plug on cylinder 5, typically an open heating element or a shorted internal coil
  2. Damaged or corroded electrical connector at the cylinder 5 glow plug
  3. Chafed, broken, or shorted wiring in the glow plug harness near the cylinder head
  4. Faulty glow plug control module or relay that cannot deliver current to cylinder 5
  5. Poor engine or chassis ground connection affecting the glow plug circuit return path
  6. Loose or oxidized glow plug terminal nut creating high resistance under load

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data to confirm P06C9 is current and not a stored history code
  2. Inspect the cylinder 5 glow plug connector and harness for corrosion, chafing, or loose terminals
  3. Measure glow plug resistance with a digital multimeter and compare it to the specification for the engine
  4. Check for battery voltage and ground at the glow plug connector during the commanded glow period
  5. Test the glow plug control module output and the circuit continuity between the module and cylinder 5
  6. Replace the faulty glow plug or repair the damaged section of harness, then clear codes and verify the repair
  7. Perform a cold-start test and re-scan to confirm the code does not return after a complete drive cycle

What a glow plug code does not always mean

  • A P06C9 does not automatically condemn the glow plug itself, because a corroded connector or a chafed harness wire can produce the same incorrect current feedback.
  • Technicians often replace all glow plugs when only one is faulty, but the code is cylinder-specific and the other plugs may be perfectly serviceable.
  • A weak battery or poor ground can cause glow plug current to fall below the expected threshold and set this code even when the plug is good.
  • The glow plug control module may command all plugs on a shared circuit, so a module fault can set cylinder-specific codes that look like individual plug failures.
  • After replacement, the code may remain stored until several cold-start cycles complete, so clearing codes and verifying over time is essential.

Can I keep driving with P06C9?

The vehicle remains drivable, but cold starting will be harder and the engine may run roughly until warm, so avoid heavy loads and long idling during warm-up. Repair the fault promptly to prevent excessive cranking, battery drain, and unburned fuel from damaging the exhaust aftertreatment system.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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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