What it means
The cylinder 12 glow plug circuit is not performing within the expected range. The cause may be the glow plug, its wiring or connections, or the control circuit.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The cylinder 12 glow plug heats the cylinder to support cold starting and reduce incomplete combustion while the engine warms. The control module monitors the cylinder 12 glow plug circuit’s response and sets this code when performance is outside the expected range.
Common causes
Most likely first.
- Faulty glow plug
- Damaged or corroded wiring or connector
- Glow plug control circuit fault
Symptoms
- Glow plug warning light on (often orange coil symbol)
- Hard cold start or no start in cold weather
- White smoke from exhaust during warm-up
How to diagnose it
- Review freeze-frame and live glow plug data to see when the cylinder 12 fault occurred and whether its response differs from the other cylinders.
- Inspect the cylinder 12 glow plug connector and harness for corrosion, loose contacts, heat damage, or chafing.
- Test the cylinder 12 glow plug using the manufacturer's procedure and compare the result with the manufacturer's specification.
- Test the cylinder 12 circuit wiring and connections for continuity and unwanted resistance using the wiring diagram.
- If the glow plug and wiring pass, test the controller's cylinder 12 output and control circuit according to the manufacturer's procedure.
Common fixes
- Clean and reconnect the cylinder 12 glow plug connector securely.
- Repair damaged wiring or corroded terminals in the cylinder 12 circuit.
- Replace the cylinder 12 glow plug if it does not meet the specified test result.
- Repair the glow plug controller or its cylinder 12 output circuit if testing finds a fault.
Can I keep driving?
If the engine starts and runs normally, limited driving may be possible, but cold starting may become unreliable and warm-up emissions may rise. Avoid repeated cranking if it will not start, since it can drain the battery; repair the fault before cold-weather use.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.