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DTC codes / P06xx · Computer and output circuits / P069D

P069DCylinder 10 Glow Plug Control Circuit High

P069D indicates that the powertrain control module (PCM) has detected an abnormally high voltage on the control circuit for cylinder 10's glow plug, which is used in diesel engines to warm the combustion chamber for reliable cold starts. The PCM commands the glow plug on and monitors the circuit; a high voltage reading typically means the circuit is open, shorted to voltage, or the glow plug itself has failed in a way that prevents current flow.

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 and increased emissions during warm-up
  • In rare cases, a no-start condition in very cold weather

Common causes, most likely first

  1. Failed glow plug on cylinder 10 (open internal element)
  2. Damaged or disconnected electrical connector at the cylinder 10 glow plug
  3. Open or shorted wire in the glow plug control circuit for cylinder 10
  4. Faulty glow plug control module (GPCM) or relay affecting that circuit
  5. Corroded or loose ground connection for the glow plug circuit
  6. PCM internal driver fault for the cylinder 10 glow plug control

How to diagnose and fix it

  1. Inspect the cylinder 10 glow plug connector and wiring for damage, corrosion, or looseness; clean and reseat as needed
  2. Measure the resistance of the cylinder 10 glow plug with a multimeter and compare to the manufacturer's specification; replace if out of range
  3. Check for voltage on the control circuit with the key on and engine off; verify the PCM is commanding the glow plug on and that voltage is present at the plug
  4. Test the glow plug control module or relay by swapping with a known-good unit if accessible, or perform a functional test with a scan tool
  5. Perform a voltage drop test on the ground circuit for the glow plug to ensure a solid connection
  6. Inspect the wiring harness for chafing, shorts to voltage, or opens between the PCM and the glow plug, repairing as necessary
  7. If all external components test good, diagnose the PCM driver circuit or replace the PCM after confirming no other faults

Glow plug circuit checks that save time

  • A high voltage code on a glow plug circuit often results from an open circuit rather than a short, so a simple resistance check of the glow plug can quickly confirm a failed element.
  • The glow plug control module may set this code even when the glow plug itself is good, so testing the module's output before replacing parts is essential.
  • Corrosion inside the glow plug connector is a frequent hidden cause that can mimic a failed glow plug and is often overlooked during visual inspection.
  • On some diesel engines, a faulty glow plug can cause a misfire code for that cylinder, leading to misdiagnosis as a fuel or compression issue.
  • The PCM may command glow plugs on after engine start for emissions control, so a circuit fault can affect post-start performance even when cold starting seems normal.

Can I keep driving with P069D?

You can generally drive the vehicle, but cold starting may be difficult and the engine may run rough until warm; avoid heavy loads and extended idling until the fault is repaired, and address it promptly to prevent further damage to the glow plug system.

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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