Glow Plug/Heater Circuit B
The glow plug heater circuit for cylinder bank B isn't working properly, like a car's block heater refusing to warm up before cold starts. This prevents diesel engines from igniting fuel efficiently in cold weather.
The ECU monitors voltage and current draw from the glow plug circuit B during the preheating cycle. It detects open circuits, shorts, or excessive resistance by comparing actual current draw against expected thresholds. If voltage or current falls outside acceptable ranges, the fault is logged.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Glow Plug Circuit Voltage | 11-14V during preheat cycle | Below 10V or no voltage detected |
| Circuit Current Draw | 5-15 amps (varies by design) | Zero amps or excessive draw indicating short |
Code P0384 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, P0384 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.