Questions and Answers

Jeep Wrangler Speedometer Is Wacky Q. 2000 Jeep Wrangler. Sometimes when driving my airbag light comes on, my rpm goes to zero, my speedometer goes to zero, and my digital mileage gauge goes crazy. After that my Check Engine Light comes on. It will be like this for about 10 minutes and then everything goes back to normal. What can it be? Can you explain what it may be and where it is located? Also explain what I will be looking for. Thanks...

A. The problem is probably a bad Vehicle Speed Sensor (VSS). The VSS is located on the speedometer pinion gear adapter. If equipped with 4WD, this adapter is located on the transfer case extension (left side). If equipped with 2WD, this adapter is located on the extension housing of the transmission (left side).

If the Check Engine Light was on, a code will be stored in the PCM. That code will confirm the VSS is the cause of the problem.

You will need a scan tool to access the codes since Chrysler does not provide a procedure for retrieving or clearing Diagnostic Trouble Codes without a scan tool.

4WD Shown

Description and Operation

Vehicle Speed And Distance Sensor - PCM Input:
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.

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.