Jim Grant's Tech Tips
Pontiac Grand Am, Speedometer Problems
Q: The speedometer and
odometer are not working on my '89 Pontiac Grand Am. Does this problem
affect the gas gauge as well? What is the procedure for getting these
problems fixed? Is it an expensive job?... Marjorie
you checked the fuses? There is a 10 amp fuse marked "GAGES"
in the fuse block that provides power to the speedometer and the fuel
gauge. If the fuse is okay then diagnose the fuel gauge first. With the
ignition key on, disconnect the electrical connector (located near the
gas tank) to the gas gauge. The gas gauge should read full. Then ground
the same wire, the gauge should read empty. If the gauge passes these
function tests the problem is likely the sending unit in the gas tank.
If not, the gauge needs a close inspection. The speedometer and the vehicle's
computer receive a signal from the vehicle speed sensor. Ideally with
a computer scan tool, monitor the vehicle speed signal at the computer.
If there is no speed indicated it's likely due to a failed speed sensor.