Fuel Pump Driver Module Off Line
The fuel pump relay or driver module isn't communicating with the engine computer, like a broken walkie-talkie between the brain and the fuel pump. The engine won't get the signal to turn on the fuel pump, so fuel delivery fails.
The ECU commands the fuel pump driver module via a control circuit and monitors feedback voltage to confirm the module is responding. It detects an open circuit, short to ground, or no acknowledgment signal within expected timeframes. When the module fails to respond or voltage is absent, the fault is logged.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Fuel pump driver module feedback voltage | 5V control signal with proper response | No voltage or collapsed signal for 2+ seconds |
| Fuel pump relay circuit resistance | Less than 5 ohms coil resistance | Open circuit or greater than 10 ohms |
Code P1239 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, P1239 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.