Cylinder #4 High To Low Side Open
Cylinder #4's fuel injector circuit has an open or broken connection between its high and low side drivers in the ECU. Think of it like a light switch that's stuck open—the fuel injector can't fire properly because the electrical circuit is broken.
The ECU monitors the voltage and current flowing through cylinder #4's fuel injector driver circuit. It detects an open circuit condition when the expected voltage transitions between high and low states don't occur, indicating a broken wire, failed driver transistor, or disconnected connector.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Injector Driver Output Voltage | 0V to 12V switching pattern | No voltage transition or stuck at one state |
| Injector Current Flow | 1-4 amps during pulse | 0 amps or no measurable current |
Code P1280 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, P1280 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.