What it means
The control module has detected an incorrect condition in the cylinder 4 glow plug circuit. The code does not by itself establish that the wrong plug type was fitted.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The cylinder 4 glow plug preheats the cylinder so a diesel engine can start and combust fuel more cleanly when cold. The control module monitors the cylinder 4 circuit’s electrical response and records this code when it detects an incorrect condition, which does not by itself prove the plug type is wrong.
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
- Read freeze-frame and glow plug live data to identify the conditions behind the cylinder 4 fault and compare its response with the other cylinders.
- Inspect the cylinder 4 glow plug connector and wiring for corrosion, loose contacts, heat damage, or chafing.
- Test the cylinder 4 glow plug using the manufacturer's procedure and compare the result with the manufacturer's specification.
- Verify the installed plug is the type specified for the vehicle and check cylinder 4 circuit continuity and connections using the wiring diagram.
- If the plug and harness test correctly, check the controller's cylinder 4 output and associated control circuit.
Common fixes
- Clean and secure the cylinder 4 glow plug connector.
- Repair damaged wiring or corroded terminals in the cylinder 4 circuit.
- Replace a failed or incorrect cylinder 4 glow plug with the specified type.
- Repair the controller or cylinder 4 control circuit if testing confirms a fault.
Can I keep driving?
Driving may be possible if the engine starts and runs normally, but cold-start difficulty and white smoke during warm-up can increase. Avoid repeated cranking if it will not start, and repair the fault before relying on the vehicle in cold weather.
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.