What does it mean?
B1304 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Accessory Delay Relay Coil Circuit Failure .
Symptoms
- Courtesy lamps, sunroof or window power remain live long after the key has been removed
- Battery goes flat overnight or after a couple of days standing
- Delay timing is wrong, features either cut off immediately or never cut off
- Interior lamps stay on and cannot be switched off with the door switches
- The relay may feel warm to the touch in the junction box
Likely causes
- Coil control wire shorted to a battery-voltage feed, so the module sees the coil energised at all times
- Relay with an internally shorted or welded coil
- Harness chafed where the coil wire runs alongside a constant power circuit
- Water in the junction box bridging adjacent terminals
- Incorrect relay fitted, drawing the wrong current for the module driver
- Aftermarket accessory spliced into the delayed accessory circuit
- Failed low-side driver inside the body control module
How to fix it
- Command the relay off with a scan tool and measure the coil control terminal, battery voltage present with the relay commanded off confirms the short
- Remove the relay and measure the control terminal again to separate a shorted relay from shorted wiring
- Carry out a parasitic draw test to quantify the battery drain
- Inspect the junction box for water staining and corrosion bridging terminals
- Trace and repair the harness where it runs alongside constant power circuits
- Replace the relay if its coil measures shorted or welded
- Replace the body control module only after the wiring and relay have been cleared, then recheck the draw