P0682Cylinder 12 Glow Plug Circuit
An electrical fault has been detected in the glow plug circuit for cylinder 12, applicable to V12 diesel engines.
Definition
During commanded glow cycles the glow plug control module measures voltage and current on every individual plug circuit. P0682 sets when the cylinder 12 circuit is open, shorted, or drawing current outside its calibrated window. Symptoms are cold-start related: longer cranking, momentary rough idle and white smoke, and an illuminated MIL, with normal behavior once warm. Left unrepaired, cold-start misfire increases emissions and washes fuel past the rings of the affected cylinder.
Common causes
- Failed cylinder 12 glow plug (open element)
- Corroded, loose, or burned plug terminal
- Open or grounded wiring in the cylinder 12 circuit
- Failed glow plug control module driver
- High-resistance ground path
Common misdiagnoses
- Replacing all twelve glow plugs for a single-circuit fault
- Replacing the glow plug control module when the plug element is open
- Battery replacement for slow cold starts
- PCM replacement
Troubleshooting steps
1.Scan for glow plug codes on all cylinders
A cylinder 12-only code isolates the fault; multiple codes shift suspicion to the module or its supply.
2.Measure glow plug resistance
With the terminal off, measure the element to ground; an open reading confirms the plug has failed.
3.Inspect the circuit wiring
Trace the cylinder 12 feed for chafe, heat damage, and corrosion at both connector ends.
4.Check output during a commanded glow cycle
Activate the glow system with a scan tool and verify voltage at the cylinder 12 terminal.
5.Test the module output pin
No output at the module connector with good wiring and a good plug confirms a failed module driver.