Code 24, Vehicle Speed Sensor: Notes

Control module applies and monitors a 12-volt signal on VSS signal circuit to Vehicle Speed Sensor (VSS). VSS is connected to speed sensor buffer which alternately grounds and opens signal circuit when wheels are turning. This pulsing action takes place about 2000 times per mile. Voltage level and pulses increase with vehicle speed. Control module converts pulsing voltage to MPH. Control module uses VSS information in calculations to determine vehicle adjustments. Scan tester reading should closely match speedometer reading when wheels are turning.

1. A Code 24 sets when MPH is less than 2 MPH, transmission is not in Park or Neutral, engine speed is greater than 1400 RPM, TPS is greater than 5 percent, load condition less than 7 In. Hg vacuum, VSS signal circuit voltage is constant and all of these conditions are met for 30 seconds. These conditions are met during a road load deceleration.
2. A steady 8-12 volts at control module connector indicates VSS circuit is open or speed sensor is faulty. A voltage of less than one volt at IP connector indicates VSS signal circuit wire is shorted to ground. Disconnect vehicle speed sensor connector. If voltage is now greater than 10 volts, vehicle speed sensor buffer is faulty. If voltage remains less than 8 volts, circuit is grounded. If circuit is not grounded, check for faulty control module connector or control module. Before replacing control module, PROM should be checked for correct application.