Code 24 - Vehicle Speed Sensor
The ECM applies and monitors a 12-volt signal on circuit 437. This circuit is alternately grounded by the Vehicle Speed Sensor (VSS) as the drive wheels turn. The ECM interprets the time between these pulses (about 2000 per mile) as vehicle speed.
Code 24 indicates that the ECM has seen a vehicle speed signal of less than 10 MPH for more than 10 seconds with engine speed over 200 RPM.
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, pulsing action will result in voltage signal variation which decreases with increased speed to an average of 4-6 volts at 20 MPH.
- Voltage of less than 1 volt at the ECM connector indicates that circuit 437 is shorted to ground. Disconnect circuit 437 at the VSS. If voltage now reads about 10 volts, the VSS is faulty. If voltage remains less than 10 volts, then circuit 437 is grounded. If 437 is not grounded, check for a faulty ECM connector or ECM.
- A steady 8-12 volts at the ECM connector indicates an open in circuit 437 or a faulty VSS.
- Normal voltage condition (indicates a possible intermittent condition).