Fuel Level Input Circuit Low
The fuel level sensor is sending a signal that's too weak or disconnected, like a radio station losing signal. The engine computer can't accurately determine how much fuel is in the tank.
The ECU monitors the voltage signal from the fuel level sender unit, which varies based on fuel tank fullness. A low voltage reading below the minimum threshold indicates a circuit problem such as a broken wire, corroded connector, or failed sender. The ECU compares this voltage against expected resistance ranges to validate sensor integrity.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Fuel Level Sensor Voltage | 0.5–4.5 volts (varies by design) | Below 0.2 volts or open circuit |
| Sender Unit Resistance | 10–180 ohms (full to empty) | Near 0 ohms or infinite resistance |
Code P1204 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, P1204 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.