What it means
The control line for the glow plug on cylinder 4 is shorted to ground or the plug is internally shorted.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The glow plug in cylinder 4 heats the air in that cylinder to help a diesel engine start when cold. The engine controller monitors the cylinder 4 glow plug control circuit, and this code sets when it detects the circuit voltage or current is lower than expected, such as from a short to ground or a shorted plug.
Common causes
Most likely first.
- Control line shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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
- Record freeze-frame data and check glow plug status and related fault codes to see when the cylinder 4 circuit fault occurs.
- With the engine off and cool, inspect the cylinder 4 glow plug connector and harness for corrosion, loose pins, or insulation rubbed through to ground.
- Check the cylinder 4 glow plug and its control wire for a short to ground using the manufacturer's test procedure.
- Compare the cylinder 4 plug's electrical readings with the manufacturer's specification and with other cylinders if the design allows.
- If the plug and wiring pass, test the glow plug control module output for cylinder 4 according to the manufacturer's procedure.
Common fixes
- Clean or repair corroded or loose contacts at the cylinder 4 glow plug connector.
- Repair chafed cylinder 4 control wiring and restore its insulation.
- Replace the cylinder 4 glow plug if it is internally shorted or outside specification.
- Repair or replace the glow plug control module if its cylinder 4 output is faulty.
Can I keep driving?
If the engine runs normally, a short local trip may be possible, but cold starts can become difficult and exhaust smoke may increase during warm-up. Avoid repeated long cranking, which can drain the battery and strain the starter.
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.