Jeep Cherokee

 Service Manual

Fuel system » Fuel injection system » Description and operation
Vehicle speed and distance sensor- pcm input

DESCRIPTION

The 3-wire Vehicle Speed Sensor (VSS) is located on the speedometer pinion gear adapter. If equipped with 4WD, this adapter is located on the extension housing of the transfer case (drivers side). If equipped with 2WD, this adapter is located on the left side of the transmission extension housing.

OPERATION

The VSS is a 3-circuit (3-wire), magnetic, hall-effect sensor.

The 3 circuits are:

•  A 5-volt power supply from the Powertrain Control Module (PCM).
•  A ground is provided for the sensor though a low-noise sensor return circuit in the PCM.
•  An input to the PCM is used to determine vehicle speed and distance traveled.

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

Powertrain control module (PCM)

Modes of operation

Automatic shutdown (asd) relay sense-pcm input

Battery voltage-pcm input

Brake switch-pcm input

Five volt sensor supplies-primary and secondary

Fuel level sensor-pcm input

Engine coolant temperature sensor-pcm input

Extended idle switch-pcm input

Oxygen sensor-pcm input

Ignition circuit sense-pcm input

Intake manifold air temperature sensor-pcm input

Manifold absolute pressure (map) sensor-pcm input

Oil pressure sensor-pcm input

Power grounds

Power steering pressure switch- pcm input

Sensor return-pcm input

Throttle position sensor (tps)-pcm input

Vehicle speed and distance sensor- pcm input

Auto shutdown (asd) relay-pcm output

CCD bus (+/-) circuits-pcm outputs

Data link connector-pcm input and output

Fuel injectors-pcm output

Fuel pump relay-pcm output

Idle air control (iac) motor-pcm output

Radiator fan relay-pcm output

Throttle body