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DTC codes / P06xx · Computer and output circuits / P069C

P069CCylinder 10 Glow Plug Control Circuit Low

P069C indicates that the powertrain control module (PCM) has detected a low-voltage condition on the control circuit for cylinder 10's glow plug, which is used in diesel engines to aid cold starting. The PCM expects a specific voltage on the control wire when the glow plug is commanded on, and a reading below the threshold triggers this code.

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

Symptoms you may notice

  • Illumination of the check engine light (malfunction indicator lamp, MIL).
  • Hard starting or rough running when the engine is cold, especially in low temperatures.
  • Excessive white smoke from the exhaust after a cold start due to incomplete combustion.
  • Engine misfire or rough idle until the engine warms up.
  • Often no symptoms besides the warning light, particularly in mild climates.
  • Possible reduced fuel economy during warm-up.

Common causes, most likely first

  1. Faulty glow plug on cylinder 10 (open or shorted internally).
  2. Damaged or corroded wiring or connector at the cylinder 10 glow plug.
  3. Open or shorted control circuit between the glow plug control module and the glow plug.
  4. Failed glow plug control module (also called glow plug relay or controller).
  5. Poor ground connection for the glow plug circuit.
  6. PCM internal fault affecting the control circuit (rare).

How to diagnose and fix it

  1. Inspect the glow plug connector and wiring at cylinder 10 for damage, corrosion, or loose pins; repair as needed.
  2. Measure the resistance of the cylinder 10 glow plug with a multimeter and compare to specifications; replace if out of range.
  3. Check for battery voltage at the glow plug connector when the key is turned on (during glow plug pre-heat); if absent, trace the circuit back to the control module.
  4. Test the control circuit for continuity and shorts to ground or power; repair wiring as necessary.
  5. Verify the glow plug control module is receiving power and ground and is functioning correctly; replace if faulty.
  6. Clear the diagnostic trouble codes (DTCs) and perform a cold-start test to confirm the repair.
  7. If the code persists after all external checks, consult factory service information for PCM diagnostics and reprogramming or replacement.

Glow Plug Circuit Low: Beyond the Plug

  • A low circuit code often results from a glow plug that has failed open, causing the control module to see low voltage on the feedback line, so the plug itself is the most common culprit.
  • Corroded terminals at the glow plug are frequently overlooked because they can mimic a failed plug; always inspect and clean connectors before replacing parts.
  • The glow plug control module may set this code for multiple cylinders if its internal switching fails, but P069C specifically points to cylinder 10, so focus diagnostics there first.
  • In some vehicles, the glow plug circuit is monitored only during the initial key-on pre-heat cycle, so intermittent faults may not set the code until a cold start.
  • A weak battery or charging system issue can cause low voltage on the control circuit and trigger this code, so always verify battery condition and connections.

Can I keep driving with P069C?

You can generally continue driving with this code, but cold starting may be difficult and the engine may run rough until warm; avoid prolonged driving with a misfire and address the issue before winter or cold weather to prevent starting problems.

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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