Code 24 - Vehicle Speed Sensor (VSS)
The ECM applies and monitors 12 volts on circuit 437. Circuit 437 connects to vehicle speed sensor which alternately grounds circuit 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile and ECM calculates vehicle speed based on time between pulses.
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- This test monitors ECM voltage on circuit 437. With drive wheels turning, pulsing action varies voltage. This variation is greater at low speeds to an average of 4-6 volts at about 20 mph (32 km/h).
- This test checks for a grounded circuit. A voltage of less than 1 volt indicates circuit 437 is shorted to ground. Disconnect circuit 437 at VSS. VSS is faulty if voltage now reads more than 10 volts. If voltage remains less than 10 volts, circuit 437 is grounded. If wire isn't grounded, check for faulty ECM connector or ECM.
- A Scanner display of "0" MPH would normally indicate a faulty circuit 437, VSS or ECM. If Scanner displays a MPH reading, Code 24 may have been caused by a faulty Park/Neutral switch circuit.
- A steady 8-12 volts at ECM connector indicates circuit 437 is open or a faulty VSS.
- Normal voltage is 1-6 volts and varying. This may indicate an intermittent problem if Code 24 is shown.
NOTE:
To prevent misdiagnosis, the technician should review electrical section or electrical troubleshooting manual and identify the type of vehicle speed sensor used prior to using this chart. Disregard Code 24, if set when drive wheels are turning.