Code 24, Vehicle Speed Sensor (VSS)
The ECM applies and monitors 12 volts on circuit 437. Circuit 437 connects to the VSS which alternately grounds circuit 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile and the ECM will calculate vehicle speed based on time between pulses.
CAUTION:
To prevent misdiagnosis, the type of VSS should be identified prior to using this procedure. Disregard a Code 24 set when drive wheels are not turning.
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- This test monitors ECM voltage on circuit 437. With wheels turning, a varying voltage will be present. Variation will be greater at low wheel speeds to an average of 4-6 volts at about 20 MPH.
- Less than 1 volt at ECM connector indicates circuit 437 wire is shorted to ground. Disconnect circuit 437 at VSS. If voltage now above 10 volts, VSS is faulty. If less than 10 volts, then circuit 437 is grounded.
- A steady 8-12 volts at ECM connector indicates circuit 437 is open or a faulty VSS.
- This normal voltage and indicates possible intermittent condition.