The function diagram for the VSS includes the following:
• VSS
• Electronic Control Module (ECM)
• World Transmission Electronic Control (WTEC) ECM
• Cruise Control
• Power Takeoff
• Road Speed Limit
Function
The VSS is on the left side of the transmission. The VSS reads the rotation of a 16 toothed gear and produces a sine wave signal. The ECM processes the sine wave signal to calculate vehicle speed. The Drivetrain Datalink (CAN 1) transmits the calculated speed to the speedometer. The calculated speed also assists in control strategies that include Cruise Control, Power Takeoff, and Road Speed Limiting.
Allison WTEC MD, HD, and 2000 series transmissions use an internal VSS that sends a signal to the transmission module.
The transmission module processes the signal and sends a square wave signal to the engine ECM.
