With 4L80E Automatic Transmission

DTC 24 4WD (91PCM6):

VSS Circuit 4WD (91PCM6):

Circuit Description:
The vehicle speed sensor circuit is the magnetic induction type. Gear teeth pressed on the outside diameter of the output carrier assembly induce an alternating current in the VSS sensor. Vehicle speed is taken from the transfer case, relayed to the VSS buffer, and is used for vehicle speed. The transmission output speed sensor signal from the transmission is sent directly to the PCM: DTC 24 will set when engine speed is between 1400- 4000 RPM and the vehicle speed sensor signal is below 200 RPM for 5 seconds, and Park/Neutral (P/N) not selected.

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

1. The first test checks the output speed sensor signal at the PCM.

2. The second test directly checks the output speed sensor operation.

Diagnostic Aids:
Check all connections especially at the transmission pass-thru connector. Refer to "Intermittents".
Check input speed sensor reading. A faulty input speed sensor during start-up will cause the PCM to read output at 0 RPM.
For internal transmission problems, refer to of appropriate vehicle service manual.