Fuel Gauge: Description and Operation

A hinged float arm in the fuel tank contacts a variable resistor in the gauge sending unit. The varying resistance in the fuel gauge circuit registers on the instrument panel gauge. Resistance in the circuit is lowest when the fuel tank is full and float arm is raised. The resulting high current flow causes the instrument panel gauge to indicate Full.

TROUBLESHOOTING

1. Disconnect electrical connector from fuel tank sending unit and attach connector to a known good sending unit.
2. Connect a jumper wire between sending unit fuel pickup tube and a good ground.
3. Secure sending unit float arm in the empty stop position and turn ignition On. Within two minutes, the gauge should read Empty, plus one pointer width or minus two pointer widths.
4. Move float arm and secure in the full stop position. Within two minutes, the gauge should read Full, plus two pointer widths, or minus one pointer width.
5. If fuel gauge does not operate as specified, check the following:
a. Wiring and electrical connections between sending unit and connector.
b. Wiring and electrical connections between connector and printed circuit board terminals.
c. Circuit continuity between printed circuit board terminals and gauge terminals.
d. Voltage limiter performance.
6. If fuel gauge operates as specified with known good sending unit, check fuel tank and original sending unit as follows:
a. Remove sending unit from fuel tank.
b. Connect sending unit wire and jumper wire as previously described.
c. If fuel gauge now operates as specified, check sending unit for damage, obstructions or improper installation and correct as necessary.