Cherokee 2WD L4-150 2.5L VIN P MFI (1991)
Distance Sensor: Description and Operation
Vehicle Speed Sensor (typical)
This sensor is located in the extension housing of the transmission (2 WD), or the extension housing of the transfer case (4 WD), and it generates 8
voltage pulses for every revolution of the output shaft. These pulses are sent directly to the Single Board Engine Controller II (SBEC II). These signals
are used to determine distance traveled and vehicle speed. The SBEC also uses these signals, along with the signals from the Throttle Position Sensor
(TPS), to determine the difference between a closed throttle deceleration condition and a closed throttle idle (vehicle stopped) condition.
Under idle (vehicle stopped) conditions, the SBEC II receives a closed throttle signal from the Throttle Position Sensor (TPS) and it also sees that there
are no signals being generated from the vehicle distance (speed) sensor. The engine controller adjusts the Automatic Idle Speed (AIS) motor to maintain
a desired engine idle speed. Under closed throttle deceleration, the engine controller receives a closed throttle signal from the Throttle Position Sensor
(TPS) and a signal from the vehicle distance (speed) sensor, because the vehicle is still moving, and it adjusts the Automatic Idle Speed (AIS) motor to
maintain a desired MAP value.
The vehicle distance (speed) sensor input signal is also used as a mileage reference for the Emissions Maintenance Reminder Light (EMR), and also to
maintain speed control operation.