With 4L80E Automatic Transmission

DTC 24 2WD (91PCM6):

VSS Circuit (2WD):

Circuit Description:
The Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction type sensor, Vehicle Speed Sensor (VSS) buffer module and wiring. Gear teeth pressed on the outside diameter of the output carrier assembly induce an alternating current in the sensor. The VSS buffer compensates for various axle ratios and converts the signal to a square wave for use by the speedometer, cruise control and antilock brake system. DTC 24 will set when vehicle speed is less than 1 mph, engine speed between 1400 and 4000 RPM, ECT greater then 60°C and MAP less than 21.8 kPa.
If the input speed sensor is not operational at start up, this can cause the vehicle speed sensor to read zero.

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

1. Verifies power and ground to VSS buffer module.

2. The first test checks the vehicle speed sensor signal to the PCM.

3. Test two checks the vehicle speed sensor signal to the vehicle speed signal buffer.

4. Test three directly verifies the vehicle speed sensor signal.

Diagnostic Aids:
Check all connections especially at the transmission pass-thru connector. Refer to "Intermittents".