How to Test a Fuel Pump Relay on a 2002 GMC Yukon Denali


The fuel system in the 2002 GMC Yukon has several electronic checking points. One of those checking points is the fuel pump relay. This relay opens the power circuit when the ignition is cut off, by releasing a switch. It closes the switch once the ignition is turned on to allow power to reach the pump. This relay can go bad in a few ways; so detailed testing is required to check for proper operation. However, the actual testing process is not difficult, it simply requires attention to detail.

Things You'll Need

  • 3 test wires with alligator clip ends
  • Multimeter
  • Pull the fuel pump relay from the fuse block by pulling upward with a slight wiggling motion. The fuel pump relay is the closest relay to the center of the box; view the relay map under the fuse box lid as a guide.

  • Read the circuit map on the top of the relay. Notice one side has a straight line with a small coil and one has a line that is broken. The straight line with the coil is the power side; the broken side is the switch side.

  • Turn the relay upside down, exposing the metal prongs. These prongs are in the same pattern as the circuit map on the top of the relay.

  • Connect one test wire to the positive terminal of the Yukon's battery, using the alligator clip; connect the other test wire to the negative terminal.

  • Connect the opposite ends of the test wires to the two prongs that match up with the power side of the circuit map, using the alligator clips. Listen for a faint clicking sound. The lack of a clicking sound means that the power circuit has too much resistance or the coil has failed. This means a new relay is required. If a clicking sound is heard, continue testing.

  • Place the third test wire on the positive battery terminal, using the alligator clip; connect the other end to either of the terminals on the switch side.

  • Turn the multimeter to 12-volt testing. Place the positive lead on the one remaining prong on the relay and the negative lead to the negative post on the Yukon's battery.

  • Read the voltage reading on the multimeter's screen, it should read approximately 12 volts. If the reading is less than 11 volts, the resistance is too high and the relay must be replaced.

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  • Photo Credit 12 volt relais, relay image by Sascha Zlatkov from
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