What does it mean?
B1204 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Fuel Gauge Sender Unit Circuit Malfunction (Short To Ground) .
Symptoms
- Fuel gauge pegged at full or at empty and refusing to move
- Low fuel warning behaving illogically: on with a full tank, or never coming on
- Range or distance to empty display wrong or missing
- Gauge briefly correct after a key cycle and then jumping to one end
- Fault message stored with the gauge stuck
Likely causes
- Sender signal wire chafed against the body, a tank strap or a heat shield and grounding out
- Water and corrosion in the fuel pump module connector bridging the signal to ground
- Sender potentiometer worn through internally so the wiper contacts the grounded end of the track
- Harness pinched where it passes through a body grommet or under a floor panel
- Poor repair splice or a wire routed against a sharp edge after previous tank work
- Damage caused during fuel pump, tank or exhaust replacement
- Failed input circuit inside the module holding the line low
How to fix it
- Compare the fuel level reported in live data with the amount actually in the tank
- Unplug the sender connector at the tank and measure the signal wire to ground: still shorted means a harness fault
- Trace the harness from the tank to the module looking for chafe points, grommet damage and crushed sections
- Inspect the tank-top connector for water ingress and green corrosion in the cavities
- Measure the sender resistance through the full float travel and compare with specification
- Repair or replace the damaged harness section, or replace the sender/pump module if the short is internal
- Clear the code, refuel and confirm the gauge tracks smoothly from full to low