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How to Troubleshoot a Fuel Gage

by Michelle Schaefer

A properly operating fuel gauge is one of the most important instruments to have on any type of motor vehicle. Being able to correctly monitor the amount of fuel available allows you to avoid running out of fuel and being stranded. On some vehicles such as airplanes and boats, running out of fuel can also be deadly. Although normally reliable, fuel gauges do go bad from time to time. Diagnosing why your fuel gauge in not working properly can not only save you money, but it can also save you from an embarrassing break down on the side of the road.

Turn the key switch to the "On" position but do not start the vehicle. Connect the red lead of the multimeter to the "I" or power terminal of the fuel gauge. Connect the black lead of the multimeter to the "G" or ground terminal of the gauge. The multimeter should indicate 12 volts. If 12 volts are not present, check the fuel gauge fuse and wiring for defects. Repair or replace as required.

Check the fuel gauge ground by connecting the red lead of the multimeter to a known good 12-volt source. Connect the black lead of the multimeter to the ground terminal of the gauge. If 12 volts is indicated on the multimeter then the ground connection to the gauge is good. If no voltage is showing on the multimeter, then the ground connection to the gauge, ground wire, or ground connection is bad. Repair the ground source as required and retest.

Turn the key switch to the "Off" position. Connect a jumper wire between the "S" terminal of the gauge and the "G" or ground terminal. Turn the key switch to the "On" position but do not start the vehicle. If the gauge reads "Full" then the gauge is good. If the gauge reads less than "Full" then the gauge is defective and must be replaced.

Remove the sending unit lead wire from he sending unit on the fuel tank if the gauge reads "Empty" but the gauge checks out good in Step 3. Turn the key switch to the "On" position but do not start the vehicle. Ground the sending unit wire to a known good ground using a jumper wire. If the gauge reads "Full" then the sending unit in the fuel tank is defective and must be replaced.

Remove all jumper wires and multimeter connections. Replace any panel covers or other vehicle components that may have been removed for access.

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About the Author

Michelle Schaefer began writing in 1998 for "The Pennsylvania Homeschooler" with advice for parents educating their handicapped children at home. She earned a bachelor's degree in education from Kutztown University in 1991.

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