P0681Cylinder 11 Glow Plug Circuit
An electrical fault has been detected in the glow plug circuit for cylinder 11, applicable to V12 diesel engines.
Definition
The glow plug control module monitors each individual plug circuit for correct voltage and current draw during pre-glow and after-glow phases. P0681 sets when the cylinder 11 circuit shows an open, a short, or abnormal current. A single failed plug on a twelve-cylinder diesel may cause only slightly longer cranking and brief white smoke in cold weather along with the MIL, but the underlying misfire on cold starts still raises emissions. Warm starting and warm driveability are typically unaffected.
Common causes
- Failed cylinder 11 glow plug (open heating element)
- Corroded or damaged connector at the plug terminal
- Wiring open or short in the cylinder 11 feed circuit
- Failed output driver in the glow plug control module
- Poor ground connection for the circuit
Common misdiagnoses
- Full glow plug set replacement for one bad circuit
- Glow plug control module replacement without testing the plug
- Battery or starting system repairs
- PCM replacement
Troubleshooting steps
1.Pull codes from the glow plug system
Confirm whether cylinder 11 is the only flagged circuit before condemning any parts.
2.Test plug resistance
Measure the cylinder 11 element to ground and compare against a known-good cylinder; open or far-out-of-spec readings condemn the plug.
3.Inspect wiring and terminals
Look for burned terminals and insulation damage along the cylinder 11 harness branch.
4.Verify commanded output at the plug
During a commanded glow cycle, confirm supply voltage is present at the cylinder 11 terminal.
5.Confirm repair on a cold start
Clear the code and recheck after a cold soak so the glow diagnostic actually runs.