Cylinder 7 Glow Plug Circuit
The glow plug for cylinder 7 isn't heating up properly before engine start, similar to a heating element in an oven failing to warm up. This prevents diesel fuel from igniting efficiently in cold conditions.
The ECU monitors the glow plug circuit's voltage and current draw during the glow plug ON cycle. It detects open circuits, shorts, or resistance faults by comparing actual voltage/current against expected parameters. A fault occurs when the circuit fails to achieve proper heating resistance or shows abnormal electrical behavior.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Glow Plug Circuit Voltage | 11-14V during glow cycle | <8V or >15V, or no voltage detected |
| Glow Plug Current Draw | 15-25A per plug | <5A (open) or >30A (short) |
Code P0677 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0677 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.