Cylinder 12 Glow Plug Circuit
The glow plug for cylinder 12 isn't heating up properly, like a car's pre-heater not working before starting a diesel engine. The engine control unit detected an electrical problem in the circuit that powers this heating element.
The ECU monitors voltage and current draw through the glow plug relay circuit for cylinder 12. It verifies the heating element reaches proper temperature before fuel injection. A fault occurs when voltage is too low, resistance is too high, or the circuit opens unexpectedly.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Glow Plug Circuit Voltage | 11-14V during glow phase | Below 8V or circuit open |
| Glow Plug Resistance | 0.5-2 ohms cold | Above 5 ohms or infinite (open) |
Code P0682 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, P0682 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.