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).
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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 .
- 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.
- 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.
- 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.