P0677Cylinder 7 Glow Plug Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Modern diesel glow systems switch each glow plug through its own power semiconductor (in a glow plug module or the engine module), so current and faults can be measured per plug. CARB requires glow plugs to be checked for current and voltage drop and, since model year 2010, a single faulty plug to be detected and named. P0677 means the load circuit of the cylinder 7 glow plug is open while glowing. Thresholds: GM engine-module drivers 200 kΩ or more (10 of 20 samples, two trips), GM's L5P glow module less than 4.0 A, Ford's 2023 6.7 L Power Stroke less than 1 A (cylinders 7 and 8 exist only on the V8). Older GM systems (LB7, LML) report open and short under this code. GM fixed false glow plug codes on 2017–20 heavy-duty diesels by reprogramming the glow module.
- What you may notice
- Check engine light (GM also glow plug lamp)
- Harder cold start in low temperatures
- Rough idle and white smoke after a cold start
- Often no symptoms when warm
- Likely causes
- LikelyGlow plug cylinder 7 burnt out (element open)
- PossiblePlug connector loose or corroded, terminal nut loose, wire broken
- PossibleGlow module supply or ground (several cylinder codes at once)
- RareGlow module or driver faulty, or software (GM bulletins)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.