Glow Plug Circuit Low Input (Bank #1)
The glow plug circuit for Bank #1 is receiving a lower electrical signal than expected, similar to a dimmer light switch not providing enough power to the bulbs. The engine computer detects this voltage drop and triggers a fault code because the glow plugs won't heat up properly for cold diesel starts.
The ECM monitors the voltage and current supplied to the glow plug relay and heating elements in Bank #1. It expects a specific voltage range during the glow plug pre-heat cycle before engine cranking. When the measured voltage drops below the threshold, the ECU registers a low-input fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Glow Plug Circuit Voltage | 10.5-14.5V during pre-heat cycle | Below 8V or open circuit condition |
| Glow Plug Relay Current Draw | 15-40A during heating | Below 5A or no current detected |
Code P1396 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, P1396 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.