B1204: Fuel Sender Circuit Short To Ground

B1204 is a body electronics code indicating that the fuel sender circuit has an unintended short to ground. The fuel sender is the sensor inside the fuel tank that reports fuel level to the instrument cluster. The body control module monitors the signal voltage on this circuit, and when it detects that the voltage has been pulled to ground rather than varying as expected with tank level, it stores B1204. The result is typically an incorrect fuel gauge reading, a gauge sitting on empty regardless of actual fuel level, or a warning lamp on the dash.

The short to ground most commonly occurs in the wiring harness running from the fuel sender connector to the BCM, particularly where the harness is routed near the fuel tank, chassis, or heat sources that can cause insulation degradation over time. A corroded or damaged sender connector at the tank can also pull the circuit low. Start by inspecting the harness and connectors for visible chafing or corrosion. A basic wiring diagram and multimeter will allow you to isolate whether the fault is in the harness, the connector, or within the sender unit itself.

This is a medium-severity fault. Your car will continue to run normally, but you cannot reliably trust your fuel gauge while B1204 is active, which creates a genuine risk of running out of fuel unexpectedly. Get it sorted at your next available opportunity, and in the meantime keep an eye on the odometer to estimate fuel consumption until the circuit is repaired.