Speedometer & Odometer Do Not Operate Properly
- Disconnect DRAC and turn ignition on. Check for 12 volts between Brown wire and ground. If 12 volts is present, go to next step. If voltage reading is less than 12 volts, check for open in Brown wire.
- Check for 12 volts between Brown wire and Black/White wire at DRAC harness connector. If 12 volts is present, ground circuit is okay. If voltage reading is less than 12 volts, check for open in Black/White wire circuit.
- Raise and support vehicle with drive wheels off of ground. Start engine and shift transmission to drive. Check for AC voltage between Purple/White and Light Green/Black wires of DRAC.
- Voltage should change when wheel speed increases or decreases. If AC voltage is not present, check for short or open in Purple/White and Light Green/Black wires. If wiring is okay, replace speed sensor.
- Raise and support vehicle. Start engine and shift transmission to drive. Check for AC voltage at DRAC speedometer output terminal by backprobing ECM/PCM connector terminal A10 (without 4L80-E transmission) or B11 (with 4L80-E transmission). Replace DRAC if AC voltage is not present.
- Raise and support vehicle. Start engine and shift transmission to drive. Check for AC voltage between Light Blue/Black and Black/White wires at DRAC connector. If AC voltage changes with wheel speed, replace DRAC.
Courtesy of GENERAL MOTORS CORP.