P0677 means Cylinder 7 Glow Plug Circuit. The glow plug controller has detected an open or out-of-range circuit for the cylinder 7 glow plug. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0677 means
Many diesel engines use glow plugs to heat each combustion chamber so the engine can start in cold weather; others, including Cummins engines in Ram pickups, use an intake air heater instead. A glow plug control module or relay switches the plugs on before and after a cold start and monitors each circuit. Glow plug codes usually point to one failed plug, its wiring, or the controller that feeds them all, and the symptoms show up mainly in cold weather.
P0677 symptoms
- Harder starting in cold weather
- Rough running or white smoke for the first minutes, often on cylinder 7
- Check engine or glow plug light
Common causes of P0677
- Failed glow plug in cylinder 7
- Damaged connector or wiring at the plug
- Fault in the glow plug controller output
How to diagnose P0677
- Unplug the glow plug and measure its resistance; an open plug confirms it
- Check the connector and harness near the valve cover
- Check for voltage at the plug during the glow cycle
Can you drive with P0677?
Yes in warm weather; expect hard cold starts until it is fixed.
P0677 tips
Cylinder 7 and 8 glow plug codes only appear on V8 diesels; check the plug and wiring on the correct bank.
Will P0677 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0677 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0380 | Glow Plug/Heater Circuit A |
| P0670 | Glow Plug Module Control Circuit |
| P0683 | Glow Plug Control Module to PCM Communication Circuit |
Guides that help
When it is more than a sensor
Glow plug faults are almost always fixed with plugs, wiring or the controller rather than major parts. If hard starting turns out to be low compression or injector problems, see how long diesel engines last and compare replacement engines on our Cummins engines page.
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