Powertrain Controls - ECM/PCM

DTC 24 Chart:

Vehicle Speed Sensor (VSS) Circuit:

CIRCUIT DESCRIPTION
The PCM receives a varying voltage signal (unbuffered) from the Vehicle Speed Sensor (VSS) located in the transaxle assembly and converts this unbuffered signal to vehicle speed (buffered signal). The unbuffered voltage level and number of pulses will increase with vehicle speed. The PCM sends the buffered signal (mph) to the instrument panel for operation of the speedometer and to Tech 1. If the PCM detects a buffered vehicle speed of 5 mph or less and the transaxle turbine shaft speed is 3000 RPM or greater, DTC 24 will set.

DTC 24 WILL SET WHEN
- DTCs 28, 56, and 91 are not set.
- Buffered vehicle speed is less than 5 mph or less.
- Transaxle turbine shaft speed is 3000 RPM or greater.
- The transaxle indicates a forward gear

ACTION TAKEN (PCM WILL DEFAULT TO)
- With a current DTC 24 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
- The PCM will disable the cruise control system, Torque Converter Clutch (TCC), and upshift will be late and hard. The PCM will calculate the mph from the transaxle turbine shaft speed and the current gear (gear ratio) and use this mph value. This calculated value will not be sent to the speedometer or Tech 1 tool.

DTC 24 WILL CLEAR WHEN
The fault no longer exists.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If DTC 24 is current, the fault is present and can be diagnosed directly. If DTC 24 is stored as history, use DTC 75 to diagnose because fault is intermittent.
2. The vehicle speed sensor will generate a frequency of greater than 0 Hertz when spun by hand. If it does, the PCM may be at fault. If it does not, check wires/sensor for opens and shorts.

DIAGNOSTIC AIDS
Check for Electromagnetic Interference (EMI) induced on CKTs 400 and 401 by running along side spark plug wires or high power transmitters (like mobile radios) operating in the vicinity.