Faulty or degraded cylinder 12 glow plug (high or low resistance); Corroded, loose or damaged connector or terminal at the cylinder 12 glow plug; Damaged, chafed or high-resistance wiring between the glow plug control module and the glow plug; Poor power or earth supply to the glow plug control module or its fuse; Fault in the glow plug control module or the driver for that output; Outdated or faulty control unit software where the manufacturer has a known fix.

P06C4

Cylinder 12 Glow Plug Circuit Range/Performance.

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
C4: FaultThe specific fault in that area

What it means

P06C4 is a generic code meaning the engine control unit has found the glow plug circuit for cylinder 12 operating outside its expected range or performance. The control unit monitors current draw, voltage or feedback from the glow plug output, and it saw values that did not match what it expected. This code only applies to engines with at least twelve cylinders, so it is rare and the exact glow plug control layout depends on the model and engine.

Symptoms

Malfunction indicator or glow plug warning light on
Harder or longer cold starting, especially in cold weather
Rough running or white smoke for a short time after a cold start
Slightly higher emissions or fuel use when the engine is cold
Other glow plug circuit codes stored alongside it

Possible causes

Faulty or degraded cylinder 12 glow plug (high or low resistance)likely
Corroded, loose or damaged connector or terminal at the cylinder 12 glow pluglikely
Damaged, chafed or high-resistance wiring between the glow plug control module and the glow plugpossible
Poor power or earth supply to the glow plug control module or its fusepossible
Fault in the glow plug control module or the driver for that outputrare
Outdated or faulty control unit software where the manufacturer has a known fixrare

How to diagnose

Read all stored and pending codes and note any other glow plug or cylinder-specific codes, then review the freeze frame data for engine temperature and battery voltage.
Check battery condition and charging voltage, as low voltage can cause range or performance faults.
Inspect the glow plug wiring, connector and terminal for cylinder 12 for heat damage, corrosion, chafing and a loose fit.
Check the relevant fuses, relays and the power and earth connections to the glow plug control module, following the model's wiring diagram.
Measure the cylinder 12 glow plug resistance and compare it with the manufacturer's specification, which varies by engine.
Test the wiring from the control module to the glow plug for continuity, shorts to earth or shorts to supply, with the circuit isolated.
With a suitable scan tool, check the glow plug current or feedback values in live data and run the glow plug output test if the vehicle supports it.
Check whether a software update exists for the control unit for this model before condemning the module.

How to fix

Replace the cylinder 12 glow plug if it is out of specification, using the correct type for the engine and tightening to the specified torque.
Clean, repair or replace the damaged connector or terminal for the cylinder 12 glow plug.
Repair or replace damaged wiring between the control module and the glow plug.
Restore correct power and earth supply by replacing faulty fuses or repairing poor connections.
Replace or reprogram the glow plug control module only after the wiring and glow plug have been proven good.
Apply a manufacturer software update if one is available and applies to this fault.

Can I keep driving?

Low severity

The car can usually be driven, as glow plugs mainly help cold starting. Book it in soon, particularly before cold weather, and stop if it starts to run very roughly or other warning lights appear.

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