P0682
Cylinder 12 Glow Plug Circuit/Open.
- Generic
- Powertrain
- Generic code
- Low severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 6
- AreaComputer and output circuits
- 82
- FaultThe specific fault in that area
What it means
P0682 is the generic code for a fault in the glow plug circuit for cylinder 12, reported as an open circuit. The engine control unit (or glow plug control module) saw no current, or a voltage or feedback signal that matches a broken circuit, when it commanded that glow plug on. Cylinder 12 only exists on large diesel engines, typically V12 layouts, so the cylinder numbering and glow plug layout depend on the engine.
Symptoms
- Glow plug or engine management warning light on
- Hard starting or extended cranking when cold
- White or grey smoke on a cold start
- Rough running or misfire on one bank until warm
- Increased cold-start emissions or noise (diesel knock)
- Stored fault with no symptoms in warm weather
Possible causes
- Failed glow plug on cylinder 12 (open heating element)likely
- Damaged, corroded or loose wiring or connector between the glow plug and the control modulelikely
- Loose or corroded glow plug terminal or connection nut at the plugpossible
- Blown fuse or faulty relay supplying that glow plug circuitpossible
- Faulty glow plug control module output stagepossible
- Wiring harness chafed or broken inside the loom, or rodent or heat damagerare
- Poor earth connection affecting the circuitrare
How to diagnose
- Read all stored and pending codes and freeze frame data, noting engine temperature and battery voltage when the fault set; check for other glow plug codes.
- Check the battery is healthy and the charging voltage is correct, as low voltage can confuse circuit diagnosis.
- Visually inspect the cylinder 12 glow plug connector, terminal and harness for corrosion, heat damage, chafing and looseness.
- Check the fuses and relay for the glow plug circuit against the vehicle wiring diagram, as the layout varies by model and engine.
- With the plug disconnected, measure the glow plug resistance and compare it with the manufacturer specification; an open reading confirms a failed plug.
- Check continuity of the wiring between the module and the plug, and check supply and earth at the connector during a glow cycle.
- If the plug and wiring are good, test the control module output using the manufacturer's procedure and the wiring diagram.
- Clear the code and recheck after repair to confirm it does not return.
How to fix
- Replace the failed cylinder 12 glow plug, and consider replacing the set if they are of similar age, following the correct torque and removal procedure.
- Repair or replace damaged wiring and connectors, ensuring a secure, clean connection.
- Clean and refit loose or corroded terminals, using the correct torque on the terminal nut.
- Replace the faulty fuse or relay, and find out why it failed.
- Replace or repair the glow plug control module if its output is confirmed faulty, following the manufacturer's procedure for any required coding.
Can I keep driving?
Low severity
The car can normally be driven, but cold starts may be harder and smokier. Book it in soon, especially before winter, and avoid repeated long cranking.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.