Code 24 - Vehicle Speed Sensor
The ECM supplies a current-limited 12-volt signal on circuit No. 437. The Vehicle Speed Sensor (VSS), located in the instrument panel cluster, senses the speedometer rotating element and furnishes this information to the buffer as a pulsed signal (2 per cable revolution or 2002 pulses per mile).
The buffer assembly switches circuit No. 437 to ground for each pulse received. The ECM uses the time between pulses to determine vehicle speed.
Code 24 is set when circuit No. 437 voltage is constant (no rise and fall of voltage for 4 to 10 seconds), with engine speed between 1500 and 4400 RPM, transmission in Drive (as indicated by Park/Neutral switch), and low MAP (indicating engine deceleration).
Loss of VSS signal will affect the Torque Converter Clutch, Idle Air Control, and Fan Control (fan will not shut off above 30 MPH with A/C on).
- Checks to see if there is a VSS signal to ECM while turning a drive wheel. Voltage should vary from under 3 volts to over 6 volts as wheel is turned. Rotating wheel faster reduces variation.
- A voltage of less than one volt indicates that the circuit No. 437 wire is shorted to ground. Disconnect circuit No. 437 at vehicle speed sensor. If voltage now reads above 10 volts, VSS is faulty. If voltage remains less than 10 volts, then circuit No. 437 wire is grounded. If circuit No. 437 is not grounded, check for a faulty ECM connector or ECM.
- A steady 8-12 volts indicated circuit No. 437 is open or a faulty vehicle speed sensor.
- This is a normal voltage condition.
- If "SCAN" displays vehicle speed, check park/neutral switch CHART C1A on vehicle with automatic transmission. If switch is okay, check for intermittents.