What does it mean?
P1399 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Glow Plug Circuit Low Voltage - Cylinder 5 .
Symptoms
- MIL on and the glow plug warning lamp may flash
- Hard cold starting and extended cranking in cold weather
- White or blue smoke from the exhaust until the engine warms up
- Rough running and shaking for the first minutes after a cold start
- Reduced power on a cold engine, sometimes stalling right after start-up
Likely causes
- Open or high resistance glow plug on cylinder 5
- Corroded, loose or broken terminal and pigtail at that glow plug
- Damaged glow plug bus bar or supply strip feeding the row
- Faulty glow plug control module output for that circuit
- Low battery voltage or a poor engine ground during preheat
- Chafed harness shorting or dropping voltage on the glow plug feed
- Heavy carbon build-up seizing the plug and destroying its element
How to fix it
- Measure the resistance of every glow plug and compare them; an open or very high value identifies the faulty one
- Check the cylinder 5 terminal and pigtail for corrosion, tightness and breakage
- Measure the voltage at the plug terminal during the preheat cycle with a multimeter
- Use a clamp meter to check current draw per plug while the system energises
- Verify battery condition and charging voltage, low system voltage affects the whole circuit
- Inspect the glow plug control module, its connector and its outputs
- Replace the faulty plug carefully to avoid breaking it in a carboned bore, then retest the whole set