What it means
The control line for the glow plug on cylinder 4 is open or shorted to supply - the plug cannot be heated.
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 warms the air in that cylinder to support cold diesel starts. The engine controller monitors the cylinder 4 glow plug control circuit, and this code sets when it detects an abnormally high circuit reading, which can happen with an open circuit or a wire shorted to supply voltage.
Common causes
Most likely first.
- Open in plug or wiring
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
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
- Save freeze-frame data and check glow plug status and related codes to determine the conditions when cylinder 4 heating was lost.
- With the engine off and cool, inspect the cylinder 4 glow plug connector and harness for disconnection, corrosion, pin damage, or contact with a power source.
- Test continuity through the cylinder 4 glow plug and its wiring using the manufacturer's procedure to locate an open circuit.
- Check the cylinder 4 control wire for a short to supply voltage, following the manufacturer's circuit test procedure.
- If the plug and wiring are intact, verify the cylinder 4 output from the glow plug control module against the manufacturer's specification.
Common fixes
- Reconnect the cylinder 4 glow plug connector or clean and secure its corroded contacts.
- Repair an open or damaged section of cylinder 4 wiring.
- Reroute or repair wiring shorted against a supply source.
- Replace the cylinder 4 glow plug if it is open or outside specification.
- Repair or replace the glow plug control module if its cylinder 4 output is faulty.
Can I keep driving?
You may be able to drive if the engine runs smoothly, but cold starting can become difficult and white smoke may appear during warm-up. Avoid repeated long cranking to reduce battery drain and starter wear.
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.