Output Speed Sensor Check

Output speed sensor check. 1991 Two wheel drive models except C/K:

Circuit Description:
The output sensor is the magnetic induction type sensor, digital ratio adapter and wiring. Gear teeth pressed on the outside diameter of the output carrier assembly induce an alternating current in the sensor. On two wheel drive vehicles, this current is transmitted to a digital ratio adapter where it is passed on to the PCM/TCM. The digital ratio adapter compensates for various axle ratios and converts the signal to a square wave for use by the speedometer, cruise control, and anti-lock systems. Since vehicle speed is taken from the transfer case on four wheel drive vehicles, the transmission output sensor signal on these units goes directly to the PCM/TCM.

If the input sensor is not operational at start up, this can cause the output sensor to read zero.

Output speed sensor check. 1991 Two wheel drive models except C/K:

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Test one checks the speed signal on CKT 437 at the PCM/TCM from the digital ratio adapter.

2. Test two checks for a speed signal from the output speed sensor to the digital ratio adapter.

3. Test three checks the output speed sensor.


Diagnostic Aids:
Check all connections, especially at the transmission pass-thru connector.