P06C5
Cylinder 1 Glow Plug Incorrect.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 6
- AreaComputer and output circuits
- C5
- FaultThe specific fault in that area
What it means
P06C5 is the generic code for 'Cylinder 1 Glow Plug Incorrect'. The glow plug control module or engine control unit has seen that the cylinder 1 glow plug's electrical behaviour, such as current draw, resistance or the feedback signal, does not match what it expects. The exact test and thresholds vary by manufacturer and engine, so check the model-specific information.
Symptoms
- Engine warning light on, and possibly a glow plug or preheat warning light
- Hard starting or longer cranking on cold mornings
- Rough running, misfire or knocking for the first minute after a cold start
- White or grey smoke from the exhaust when cold
- Slightly higher fuel use and rougher idle until the engine warms up
Possible causes
- Failed or worn cylinder 1 glow plug (open circuit or abnormal resistance)likely
- Corroded, loose or damaged glow plug connector or terminal at cylinder 1likely
- Damaged, chafed or high-resistance wiring between the glow plug module and cylinder 1 plugpossible
- Poor power or earth supply to the glow plug control module, including a weak battery or corroded fuse or relay contactspossible
- Fault in the glow plug control module output stage for cylinder 1possible
- Outdated or faulty control unit software where the manufacturer has a known fix for incorrect glow plug diagnosisrare
How to diagnose
- Read all stored and pending codes and the freeze frame data. Note engine temperature, battery voltage and whether other glow plug codes are present, then check for any manufacturer service bulletins for the engine.
- Check battery condition and charging voltage, as low voltage can upset glow plug diagnostics.
- Visually inspect the cylinder 1 glow plug connector, the wiring loom and the module connector for corrosion, heat damage, chafing or looseness.
- Check the glow plug supply fuses and relay or power feed, following the wiring diagram for the engine.
- With the plug removed from its connector, measure the cylinder 1 glow plug resistance and compare it with the specification and with the other cylinders' plugs.
- Use a scan tool that supports it to activate the glow plugs. Check the current draw and the module's feedback for cylinder 1 against the other cylinders.
- Check voltage and earth at the glow plug connector during activation, and test the wiring for continuity and shorts to earth or supply.
- If the plug, wiring and supplies are good, check for a software update and suspect the glow plug control module.
How to fix
- Replace the cylinder 1 glow plug, using the correct specification and tightening to the manufacturer's torque. Take care not to snap it, as the tip can be brittle or seized.
- Repair or replace the corroded or damaged connector or terminal at cylinder 1.
- Repair or replace the damaged wiring between the module and the glow plug.
- Restore the correct power and earth supply by repairing connections, fuses or relays, and replace a weak battery if it is at fault.
- Replace the glow plug control module if its output has failed and the wiring and plug test good.
- Update the control unit software only where the manufacturer lists it as a fix for this fault.
Can I keep driving?
Medium severity
The car can usually be driven short-term, but cold starting and running may be poor and one failed plug often means others are ageing. Get it fixed soon, and stop driving if there is heavy misfire, persistent white smoke or a knocking noise.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.