Instrument Panel - Electronic: Testing: Speedometer

Prior to beginning speedometer tests, check Electronic Control Module (ECM) for any trouble codes that are present.

• If Code 24 is not present, and speedometer does not operate properly, replace instrument cluster.
• If Code 24 is set, but speedometer seems to operate properly, proceed to step 5) (VIN 9) or step 8) (VIN R).
• If Code 24 is set, and speedometer is not operating properly, proceed to step 1).
• If Code 24 is not set, and cruise control is not operating properly, proceed to step 5) (VIN 9) or step 8) (VIN R).

1. Disconnect instrument cluster connector C-1. See Fig 1 . With ignition switch in the "RUN" position, measure voltage between the Yellow/Black wire of cluster connector and ground. Voltmeter should read 12 volts. If not, check or repair Yellow/Black and Yellow wires for an open.
2. Measure voltage between Yellow/Black and Black/White wires. Voltmeter should read 12 volts. If not, check or repair Black/White wire for an open. If okay, check Black wire for good ground.
3. Reconnect instrument cluster connector C-1. See Fig 1 . Turn ignition switch to the "RUN" position. Place gear selector in Neutral and raise vehicle off ground. Check for AC voltage between Yellow/Red and Purple/White wires while turning drive wheels by hand. Correct voltage should vary between 1-5 volts AC.
4. If voltage is correct, check the printed circuits for flaws or cracks. If printed circuits are okay, check or repair the Yellow and Purple/White wires. If wires are okay and 15-pin connector under console, between seats is correctly mated, replace instrument cluster.
5. On vehicles with V6 (VIN 9) engines only, turn ignition switch to "RUN" position. Disconnect C-2 connector (located below right hand steering column support). See Fig 1 . The voltage reading between Dark Green/White wire and ground should be 12 volts. If okay, proceed to step 9). If not, check the Dark Green/White wire and Brown wire for an open circuit.
6. If circuits are okay, replace ECM. Reconnect C-2 connector below steering column support. See Fig 1 . Turn cruise control on. Disconnect 15-pin connector between seats. Measure voltage between Dark Green/White wire and ground. Voltage reading should be 12 volts.
7. If okay, see GENERAL MOTORS CUSTOM CRUISE III article in this section. If not, check Dark Green/White wire for an open circuit, and that C-2 connector below steering column support is correctly mated. See Fig 1 .
8. On vehicles with 4-cylinder (VIN R) engines only, disconnect instrument cluster connector C-1. Turn ignition switch to "RUN" position. Measure voltage between Dark Green/White wire and ground. Voltmeter should read 12 volts. If okay, proceed to step 9). If incorrect, check Dark Green/White and Brown wires for an open circuit. If okay, replace ECM.
9. Turn ignition switch to "RUN" position. Place gear selector in Neutral and raise rear wheels off the ground. Rotate drive wheels by hand and measure voltage between the Dark Green/White and ground wires. Voltage reading should vary from less than 1 volt to more than 4 volts. If voltage is correct, but Code 24 is set, replace ECM.
10. If voltage is correct, but cruise control does not operate properly, replace the cruise control unit. If voltage reading is not correct, replace instrument cluster.