Code 24, Vehicle Speed Sensor - 1992 Except 4L80-E Trans.: Notes

Fig 1: Code 24, VSS Circuit Diagram (1992 Except 4L80-E Transmission)

Courtesy of GENERAL MOTORS CORP.

Vehicle speed sensor (VSS) circuit consists of a magnetic induction type sensor, VSS buffer (DRAC) module and wiring. Gear teeth pressed on the outside diameter of the output carrier assembly induce an alternating current in the sensor. On 2WD vehicles, this current is transmitted to a DRAC module where it is passed on to ECM. DRAC compensates for various axle ratios and converts signal to a square wave for use by the speedometer, cruise control and anti-lock brake system.

Since vehicle speed is taken from transfer case on 4wd vehicles, transmission vehicle speed sensor signal on these units goes directly to PCM. Code 24 will set when vehicle speed is less than 200 RPM for 1.5 seconds while engine speed is greater than 3000 RPM. Park/Neutral is not selected. If input speed sensor is not operational at start up, vehicle speed sensor may read zero.

NOTE: Test numbers refer to test numbers in diagnostic chart.

This test checks vehicle speed sensor signal to PCM.
This test checks vehicle speed sensor signal to DRAC.
This test verifies vehicle speed sensor signal.