Code 24 - Vehicle Speed Sensor (VSS) (Integral Buffer)
The ECM supplies a current limited 12 volt signal on circuit 437. The 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 for 4-10 seconds.
- Engine speed is 1500-4400 RPM
- Park/Neutral switch indicates transmission is in Drive range.
- Low MAP (high vacuum) indicating an engine deceleration.
Loss of VSS will affect converter clutch (TCC) and idle (IAC), and fan control will not shut off above 30 MPH with A/C on.
- This test checks if there is a VSS signal to the ECM while turning drive wheel. Voltage should vary from less than 3 volts to more than 6 volts with less variation as wheel speed increases.