Faulty glow plug on cylinder 9; Damaged or corroded electrical connector at the cylinder 9 glow plug; Open or shorted glow plug wiring harness; Failed glow plug control module or relay; Poor ground connection for the glow plug circuit; Engine control module software issue or internal fault

DTC codes / P06xx · Computer and output circuits / P06C1

P06C1Cylinder 9 Glow Plug Circuit Range/Performance

Q: What does code P06C1 mean?

Cylinder 9 Glow Plug Circuit Range/Performance. P06C1 indicates that the engine control module has detected an out-of-range or poor-performance condition in the glow plug circuit for cylinder 9, typically on diesel engines with individual glow plug control. The computer monitors the circuit's electrical behavior and flags this code when the voltage or current does not match expected values during glow plug activation or self-test.

P06C1 indicates that the engine control module has detected an out-of-range or poor-performance condition in the glow plug circuit for cylinder 9, typically on diesel engines with individual glow plug control. The computer monitors the circuit's electrical behavior and flags this code when the voltage or current does not match expected values during glow plug activation or self-test.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

Illuminated check engine light, often with no other symptoms
Hard starting or rough idle when the engine is cold
Excessive white smoke from the exhaust after a cold start
Reduced fuel economy during warm-up
Misfire or rough running shortly after cold start
In rare cases, a no-start condition in very cold weather

Common causes, most likely first

Faulty glow plug on cylinder 9
Damaged or corroded electrical connector at the cylinder 9 glow plug
Open or shorted glow plug wiring harness
Failed glow plug control module or relay
Poor ground connection for the glow plug circuit
Engine control module software issue or internal fault

How to diagnose and fix it

Inspect the cylinder 9 glow plug connector and wiring for damage, corrosion, or looseness
Measure the resistance of the cylinder 9 glow plug and compare to specifications
Check for battery voltage and ground at the glow plug connector during the glow plug on-time
Test the glow plug control module and its relay for proper operation
Repair or replace any damaged wiring or connectors in the circuit
Replace the faulty glow plug if resistance is out of range
Clear the code and verify the repair with a scan tool and a cold-start test

Glow Plug Circuit Checks Before Replacement

A glow plug that tests good on resistance can still cause this code if the control module's current monitoring circuit is faulty, so always verify the module's output signal.
Corrosion inside the glow plug connector often mimics a failed glow plug, and simply cleaning the terminals can resolve the code without parts.
The code may set intermittently if the glow plug only fails when cold, so testing at room temperature can miss a marginal plug.
On some engines, a single failed glow plug can affect the entire glow plug system's self-test, leading to multiple glow plug codes being stored.
After replacing a glow plug, the engine control module may need a relearn or adaptation reset to clear the code permanently.

Can I keep driving with P06C1?

You can generally drive the vehicle with this code, but cold starting may be difficult and prolonged driving with a faulty glow plug can lead to excessive smoke and increased engine wear. Avoid heavy loads or high speeds until the issue is repaired, especially in cold weather.

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.