1. Checking the indicator.
A) Disconnect the connector from the fuel filter switch. Short the connector terminals on the wire side.
b) Remove the fuse "CHARGE" (Charger) and turn on "ignition". The indicator should light up "FILTER" and a beep will sound.
2. Checking the sound signal.
A) Connect the battery to terminals 2 (+) and 1 (-). If the horn does not work, it should be replaced.
3. Checking the sensor-switch.
A) Check for continuity between the switch terminals when the float is at the bottom.
b) Check for continuity between the switch terminals when the float is at the top.