P06C1
Cylinder 9 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
- C1
- FaultThe specific fault in that area
What it means
P06C1 means the engine control unit (or glow plug control module) has judged the cylinder 9 glow plug circuit to be operating outside its expected range or performance. The measured current, voltage or resistance for that plug did not match what was expected during a heating or diagnostic cycle. It does not always mean a total circuit failure, so a weak plug, high resistance or a poor connection can all set it. Cylinder numbering and the number of glow plug circuits depend on the engine, so confirm which physical cylinder is number 9 for the vehicle.
Symptoms
- Malfunction indicator lamp or glow plug warning lamp on
- Harder starting in cold weather
- Rough running or misfire for the first minute after a cold start
- White smoke from the exhaust on cold starts
- Slightly higher emissions or fuel use when cold
- No obvious symptoms in mild weather
Possible causes
- Worn or failing cylinder 9 glow plug with abnormal resistancelikely
- Corroded, loose or damaged connector or terminal at the cylinder 9 glow pluglikely
- Damaged, chafed or high-resistance wiring between the glow plug control module and the plugpossible
- Poor power or earth supply to the glow plug control module, or a blown fuse or relay feeding that circuitpossible
- Faulty glow plug control module output stage for that cylinderpossible
- Outdated or faulty control unit software affecting glow plug diagnostics, where the manufacturer has issued an updaterare
How to diagnose
- Read all stored and pending codes and note the freeze frame data, including coolant temperature, battery voltage and engine state, and check for other glow plug codes on neighbouring cylinders.
- Confirm which physical cylinder is number 9 on this engine using the manufacturer's data, as numbering and bank layout vary by model.
- Visually inspect the glow plug connector, terminal and wiring for corrosion, heat damage, chafing, oil contamination or loose fit.
- Check battery condition and charging voltage, then check the relevant fuses, relays and the power and earth connections to the glow plug control module.
- With the plug disconnected, measure its resistance and compare it with the specification for the engine; also check for a short to earth.
- Check the wiring for continuity and voltage drop under load from the control module to the plug.
- Use a scan tool that supports it to activate the glow plug circuit and watch current draw and commanded duty for cylinder 9 against the other cylinders.
- Check for any applicable software updates or technical bulletins for the engine before replacing the control module.
How to fix
- Replace the cylinder 9 glow plug if its resistance or current draw is out of specification, following the correct torque and removal procedure to avoid snapping the plug.
- Clean or replace the corroded or damaged connector and terminals at the glow plug.
- Repair or replace damaged wiring or the harness section between the control module and the plug.
- Restore a good power or earth supply, and replace any faulty fuse or relay, after finding why it failed.
- Replace the glow plug control module only if testing proves its output for that cylinder is faulty.
- Apply a manufacturer software update if an outdated calibration is confirmed as a known cause.
Can I keep driving?
The car can usually be driven, as glow plugs mainly help cold starts, but book it in soon. Cold starting may become difficult and a seized plug can be harder to remove the longer it is left.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.