DTC 24

Code 24 will set if:

^ CKT 38 voltage is constant.
^ Engine speed between 2,400 and 4,400 rpm.
^ Low load condition.
^ All conditions must be met for 10 seconds.

The ECM applies and monitors 12 volts on CKT 38. CKT 38 connects to the Vehicle Speed Sensor which alternately grounds CKT 38 when the drive wheels are turning. This pulsing action takes place about 4096 times per mile and the ECM will calculate vehicle speeds based on the time between "pulses".

1. This test monitors the ECM voltage on CKT 38. With the wheels turning, the pulsing action will result in a varying voltage. The variation will be greater at low wheel speeds with an average variation of 4-6 volts at about 20 mph. (32 km/h).
2. A voltage of less than 1 volt at the ECM connector indicates that CKT 38 is shorted to ground. Disconnect CKT 38 at the Vehicle Speed Sensor. If voltage now reads above 10 volts, the Vehicle Speed Sensor is faulty. If voltage remains less than 10 volts, then CKT 38 is shorted to ground. If CKT 38 is not shorted to ground, check for a faulty ECM connector or ECM.
3. A steady 8-12 volts at the ECM connector indicates CKT 38 is open or a faulty Vehicle Speed Sensor.