Code 24 - Vehicle Speed Sensor

The ECM supplies a current limited 12 volt signal on circuit 437. The Vehicle Speed Sensor (VSS) will sense the speedometer rotating element and furnish this data 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:

ECM receives no VSS signal.
Engine speed is more than 1800 RPM.
Park/Neutral switch indicates transmission is in Drive range.
For at least 25 seconds.

NOTE: The following step numbers refer to the numbers in the accompanying flow chart(s).

This test checks for a VSS signal to the ECM while turning drive wheel. Voltage should vary from 4-6 volts.
This test checks ECM and wiring harness to VSS buffer.
This test checks if ECM recognizes the VSS signal.
This is normal voltage condition and indicates a possible intermittent condition.

Fig 1: Flow Chart, Code 24: Vehicle Speed Sensor (All Engines)

NOTE: To prevent misdiagnosis, technician should identify the type of vehicle speed sensor used prior to using this chart. Disregard Code 24, if set when drive wheels are not turning.

Fig 2: Flow Chart, Code 24: Vehicle Speed Sensor (All Engines)

Fig 3: Schematic, Code 24: Vehicle Speed Sensor (All Engines)