Glow Plug Circuit High Input (Bank #2)
The glow plug circuit for cylinder bank #2 is detecting a voltage that's higher than expected, like a heating element that's getting too much electrical current. This prevents proper diesel engine cold-start assistance on that bank.
The ECM monitors the voltage drop across the glow plug circuit for bank #2 during the glow plug warm-up cycle. It expects a controlled voltage draw as the plugs heat up; an abnormally high voltage reading indicates either excessive current draw or a wiring/connector fault causing resistance changes.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Glow plug circuit voltage | 11-14V with controlled current draw | Above 14.5V or excessive current detected |
| Circuit resistance | 0.5-2 ohms per plug | Below 0.3 ohms (short) or erratic readings |
Code P1399 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, P1399 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.