Vehicle Speed Sensor (Wrangler)

NOTE: On Grand Cherokee and Liberty, the Vehicle Speed Sensor (VSS) signal is sent through Controller Anti-Lock Brake (CAB) module by a rear wheel speed sensor.

On 2WD vehicles, Vehicle Speed Sensor (VSS) is located on pinion gear adapter on transmission extension housing. See Fig 1 . On 4WD vehicles, VSS is located on transfer case extension. See Fig 2 . The VSS is a 3-circuit (3-wire), magnetic, Hall Effect sensor. The 3 circuits are as follows.

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.

Fig 1: Locating Vehicle Speed Sensor (Wrangler - 2WD Vehicles; A/T Shown)

Courtesy of DAIMLERCHRYSLER CORPORATION

Fig 2: Locating Vehicle Speed Sensor (Wrangler - 4WD Vehicles)

Courtesy of DAIMLERCHRYSLER CORPORATION