Failed or degraded cylinder 5 glow plug (open circuit or out-of-range resistance); Corroded, loose or damaged connector or terminal at the cylinder 5 glow plug; Damaged or chafed wiring between the glow plug control module and cylinder 5 plug (open or short circuit); Low battery voltage or poor earth or supply connections affecting glow plug current; Faulty glow plug control module or its output stage for that cylinder; Damaged plug tip, or a plug of the wrong specification fitted previously.

P06C9

Cylinder 5 Glow Plug Incorrect.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
C9: FaultThe specific fault in that area

What it means

P06C9 means the engine or glow plug control module has judged that the cylinder 5 glow plug is not behaving as expected. This is a diesel-specific fault. The control unit compares the plug's current draw, resistance or feedback signal with what it expects during pre-heat and post-heat, and sets the code when the value is out of range. The exact test and thresholds depend on the vehicle and glow plug system.

Symptoms

Engine warning light or glow plug warning light on
Hard starting or extended cranking in cold weather
White smoke and rough running after a cold start
Noticeable misfire or lumpy idle on cylinder 5 until the engine warms up
Higher emissions and fuel consumption on cold starts

Possible causes

Failed or degraded cylinder 5 glow plug (open circuit or out-of-range resistance)likely
Corroded, loose or damaged connector or terminal at the cylinder 5 glow pluglikely
Damaged or chafed wiring between the glow plug control module and cylinder 5 plug (open or short circuit)possible
Low battery voltage or poor earth or supply connections affecting glow plug currentpossible
Faulty glow plug control module or its output stage for that cylinderpossible
Damaged plug tip, or a plug of the wrong specification fitted previouslyrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting engine temperature, battery voltage and whether other glow plug codes are present.
Visually inspect the cylinder 5 glow plug connector, wiring and the module connector for corrosion, heat damage, chafing and looseness.
Check battery condition and charging voltage, as low voltage can cause glow plug faults.
With the engine cold and ignition off, measure the resistance of the cylinder 5 glow plug against the manufacturer's specification and compare it with the other cylinders.
Check the supply, earth and continuity of the wiring to the cylinder 5 plug, and look for shorts to earth or to supply.
Use a scan tool with live data or actuator tests, if the vehicle supports them, to watch glow plug current or status on cylinder 5 during pre-heat.
If the plug and wiring are good, check the glow plug control module output and its connections following the model-specific procedure.

How to fix

Replace the cylinder 5 glow plug, and consider replacing the full set if they are of similar age, using the correct specification and tightening torque.
Clean or repair the connector and terminals, or replace them if damaged.
Repair or replace damaged wiring between the control module and the cylinder 5 plug.
Restore battery health or repair poor supply and earth connections.
Replace the glow plug control module if testing shows it is faulty, and carry out any coding or adaptation the manufacturer requires.

Can I keep driving?

Low severity

The car can normally be driven short term, but cold starting may be poor and emissions higher, so book it in soon. Stop and get it checked if there is a persistent misfire, heavy smoke or any burning smell from the wiring.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.