Powertrain Controls - ECM/PCM

Diagnostic Trouble Code (DTC) 24:

Vehicle Speed Sensor (VSS) Circuit:

CIRCUIT DESCRIPTION
Vehicle speed information is provided to the Powertrain Control Module (PCM), by the Vehicle Speed Sensor (VSS), which is a Permanent Magnet (PM) generator located in the transmission. The PM generator produces a pulsing AC voltage. The AC voltage level and the number of pulses increases as the speed of the vehicle increases. The PCM then converts the pulsing voltage to vehicle speed which is used for calculations. The vehicle speed can be displayed with a Tech 1 scanner.

The PCM supplies a signal, on CKT 817, to the instrument cluster for operating the speedometer and odometer and to the cruise control module.

DIAGNOSTIC TROUBLE CODE (DTC) 24 WILL SET WHEN
- (Automatic Transmission) - Transmission output speed is less than 250 RPM when engine speed is greater than 3000 RPM, not in park or neutral, and DTCs 21, 22, 28, 33 and 34 not set and Manifold Absolute Pressure (MAP) greater than 20 kPa (2.9 psi) but less than 99 kPa (14.3 psi). All conditions met for 3 seconds.
- (Manual Transmission) - Transmission output speed is less than 3 RPM when engine RPM is greater than 1250 RPM, Throttle Position (TP) angle less than 1%, MAP between 11 kPa (1.5 psi) and 21 kPa (3.0 psi), DTCs 21, 22, 33 and 34 not set. All conditions met for 6 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate, transmission will default to third gear, high transmission line pressure.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. The Acceleration Slip Regulation (ASR) system must be disabled when performing this step. Whenever the ignition key is cycled to the "OFF" position and then cycled back "ON" the ASR system will default "ON."
2. If software/calibration is correct and DTC 24 sets, replace PCM.
3. Be sure harness is routed away from hot exhaust components.

DIAGNOSTIC AIDS
The Tech 1 scanner should indicate a vehicle speed whenever the drive wheels are turning.

Check CKTs 400 and 401 for proper connections to be sure they're clean and tight and the harness is routed correctly.