Vehicle Speed Sensor: Description and Operation

VEHICLE SPEED SIGNAL (VSS) - PCM INPUT
The PCM requires the VSS to be able to control the following programs:
- Speed Control
- IAC motor (during deceleration)
- Injection pulse width (during deceleration)
- OBD II diagnostics
- PCM mileage EEPROM
- Road speed shutdown
- Speedometer/Odometer (bused message)

NOTE: Road Speed Shutdown is the PCM shutting oft fuel injectors above a preset vehicle speed.

Vehicle Speed Sensor - Automatic Transmission:

Vehicle Speed Sensor - Manual Transmission:

The vehicle speed sensor is located in the transmission extension housing.

The vehicle speed sensor on 3 speed automatic and manual transaxle vehicles is a Hall-effect sensor. This sensor is mechanically driven by a pinion gear that is in mesh with the right axle drive shaft. The hall-effect sensor switches a 5 volt signal sent from the PCM from a ground to an open circuit.

Like all Hall-effect sensors, the electronics of the sensor needs a power source. This power source is provided by the PCM. It is the same 8 volt power supply that is used by the CKP and CMP sensors.

The vehicle speed sensor generates 8 pulses per sensor revolution. This signal, in conjunction with a closed throttle signal from the throttle position sensor, indicates a closed throttle deceleration to the PCM. Under deceleration conditions, the PCM adjusts the Idle Air Control (IAC) motor to maintain a desired MAP value.

When the vehicle is stopped at idle, a closed throttle signal is received by the PCM (but a speed sensor signal is not received). Under idle conditions, the PCM adjusts the IAC motor to maintain a desired engine speed.