Code 24 - Vehicle Speed Sensor (VSS) Circuit: Notes

The ECM applies and monitors 12 volts on circuit No. 437. This circuit connects the Vehicle Speed Sensor (VSS), which alternately grounds circuit No. 437 when drive wheels are turning. This pulsating action takes place about 2000 times per mile and the ECM will calculate vehicle speed based on the time between pulses. "SCAN" tester reading should closely match speedometer reading with drive wheels turning.

Code 24 will set if: circuit No. 437 is constant, engine speed is more than 200 RPM, vehicle speed signal at terminal ECM "A9" is less than 10 MPH (16 k/mh), all conditions are met for at least 10 seconds.

1. This test monitors the ECM voltage on circuit No. 437. With wheels turning, the pulsating action will result in a varying voltage. The variation will be greater at low wheel speeds to an average of 4-6 volts at about 20 MPH 32 (km/h).
2. A voltage of less than one volt at ECM connector indicates that circuit No. 437 wire is shorted to ground. Disconnect wire at VSS. If voltage now reads above 10 volts, the VSS is faulty. If voltage remains less than 10 volts, then wire is grounded. If circuit No. 437 is not grounded, check for a faulty ECM connector or ECM.
3. A steady 8-12 volt reading at the ECM connector indicates the circuit No. 437 is open or VSS is faulty.
4. Normal voltage indicates a possible intermittent condition.