How to Troubleshoot Your Fuel Gauge
Contributed By: Bill Kelsey
To check the fuel guage (from the Haynes FSJ manual):
Set the ignition switch to ON.
If the gauge pointer does not move from empty, check the
fuse. If the fuse is OK, locate the sender unit. Connect
the sending unit connector to ground. If the pointer goes to
the full position replace the sending unit. If the
pointer stays in same position, use a jumper wire to ground
the terminal on the back of gauge. If the pointer moves, the
problem lies in the wire between the gauge and the sending
unit. If the pointer does not move with the back of the gauge
grounded, check for voltage at the other terminal of the
gauge. If voltage is present, replace the gauge.
Checking the sending unit.
- Raise the vehicle and support it securely on jackstands
- If the fuel gauge on the instrument panel is
malfunctioning, check the operation of the fuel level sending
unit. If the fuel level sending unit operates in accordance
with the following test, the problem may exist in the gauge or
- Before performing any tests on the fuel level sending unit,
make sure the sending unit has a good ground electrical
- Raise the vehicle and support it securely on jackstands.
- Locate the fuel level sending unit electrical connector.
On most models, the connector is located near the back of teh
fuel tank near the fuel filler hose and the fuel vapor hose.
However, some late models are equipped with an access hole
under the rear seat or trunk area. Lift the rear seat, remove
the retaining screws and remove the access cover plate.
- Position the probes of an ohmmeter into the electrical
connector and check the resistance. Use the 200-ohm or low
scale on the ohmmeter.
- With the fuel tank completely full, the resistance should
be approximately 110 ohms. With the tank half full, the
resistance should be approximately 55 ohms. With the fuel
tank empty, the resistance sof the sending unit should be
approximately 1 ohm.
- Note: a more accurate check of the sending unit can be made
by removing it (fuel level sending unit of assembly) from the
fuel tank and checking its resistance while manually operating
the float arm.
- If the readings are incorrect, replace the sending unit.
'79 widetrack Cherokee "S"