Code 24, Vehicle Speed Sensor - Except 3.1L, C & K Series & Models With 4L80-E Transmission: Notes

Fig 1: Code 24, VSS Circuit Diagram (Except 3.1L, C, K & Models With 4L80-E Transmission)

Courtesy of GENERAL MOTORS CORP.

Fig 2: Code 24, VSS Circuit Diagram (4.3L Turbo)

Courtesy of GENERAL MOTORS CORP.

Fig 3: Code 24, VSS Circuit Diagram (G, P, R & V Series W/O 4L80-E Transmission)

Courtesy of GENERAL MOTORS CORP.

The ECM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 is connected to the digital Ratio Adapter Controller (DRAC) which alternately grounds this circuit when it is receiving voltage pulses from the Vehicle Speed Sensor (VSS). Scan test reading should closely match speedometer reading.

1. Code 24 will set if voltage on circuit No. 437 is constant, engine speed is greater than 1200 RPM, vehicle speed is less than 2 MPH vehicle is not in Park or Neutral and all conditions have been met for at least 5 seconds. These conditions are met during a road load deceleration.
2. This determines if DRAC is receiving the AC signal from the VSS.
3. This test monitors DRAC voltage on circuit No. 437. With wheels turning, pulsing voltage should be present. Voltage variation will be greater at a low speed to an average of 4-6 volts at about 20 MPH.