Code 24 - Vehicle Speed Sensor (VSS)

The ECM supplies a current limited 12 volt signal on circuit 437. The Vehicle Speed Sensor (VSS), located in the I.P. cluster, will sense the speedometer rotating element and furnish this information to the buffer as a "pulsed" signal (2 pulses per cable revolution or 2002 per mile). The buffer assembly will switch circuit 437 to ground for each pulse received. The ECM uses the time between pulses to determine vehicle speed.

Code 24 is set by the following:

Circuit 437 voltage is constant. No rise and fall of voltage for 4 to 10 seconds.
Engine speed between 1500 and 4400 RPM.
P/N switch indicates transmission selector is in Drive range.
Low MAP (High Vacuum) indicating an engine decel.

Loss of VSS will affect:

Torque Converter Clutch.
Idle Air Control.
Fan control will not shut off above 30 MPH with A/C on.
NOTE: The following step numbers refer to the numbers in the accompanying flow chart(s).

This test checks if there is a VSS signal to the ECM while turning a drive wheel. Normally voltage will vary from less than 3 volts to over 6 volts as wheel is turned slowly. Rotating the wheel faster decreases the voltage variation.

Fig 1: Code 24, VSS Flow Chart (Buffer Attached To IP Cluster)

Fig 2: Code 24, VSS Flow Chart (Buffer Attached To IP Cluster)

Fig 3: Code 24, VSS Ckt Diag. (Buffer Attached To IP Cluster)

Fig 4: Code 24, VSS Flow Chart (Remote From IP Cluster)

Fig 5: Code 24, VSS Flow Chart (Remote From IP Cluster)

Fig 6: Code 24, VSS Flow Ckt Diag. (Remote From IP Cluster)

Fig 7: Code 24, VSS Flow Chart (Buffer is Intregal W/IP Cluster)

Fig 8: Code 24, VSS Flow Chart (Buffer is Intregal W/IP Cluster)

Fig 9: Code 24, VSS Ckt Diag. (Buffer is Intregal W/IP Cluster)