1. Disconnect the electrical connector of the sensor-switch and remove the cap from the GTZ reservoir.
2. Check the freedom of movement of the sensor float. If there are signs of jamming, replace the assembly.
3a. Using an ohmmeter, check that there is no continuity between the sensor-switch connector terminals with the float raised...
3b.... and in its presence with the float lowered (see accompanying illustrations). At negative results of check replace assembly of the gauge switch.