Powertrain Controls - ECM/PCM

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION
The speed sensor circuit consists of a magnetic induction type sensor, a Vehicle Speed Signal (VSS) buffer module, 4WD low switch (when needed), and wiring. Gear teeth pressed onto the output shaft induces an alternating voltage into the sensor. This signal is transmitted to the VSS buffer module. The VSS buffer module compensates for various final drive ratios. The VSS buffer module will also convert the AC VSS signal into a 40 Pulse Per Revolution (PPR) DC signal on CKT 437 to indicate transmission output speed. On 4WD vehicles, the 4WD low signal will also be used for adjustment of the 40 PPR signal to the PCM.

DTC 24 WILL SET WHEN
^ No DTC(s) 21, 22, 28, 33, or 34.
^ Not in PIN.
^ CKT 437 voltage is constant.
^ Engine speed is greater than 3000 RPM.
^ Output speed is less than 250 RPM.
^ MAP is greater than 100 kPa.
^ TP is between 10% and 100%.
^ All conditions met for 3 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
^ Maximum line pressure.
^ Second gear only.

DTC 24 WILL CLEAR WHEN
The ignition is cycled "OFF" then "ON."

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic charts.
1. This test checks for voltage to the VSS buffer module.
2. This test checks the ground circuit to the VSS buffer module.
3. This test checks the Vehicle Speed Sensor (VSS) circuit at the VSS buffer module.
4. This test checks for an output speed signal from the VSS buffer module.

DIAGNOSTIC AIDS
^ DTC 24 will set when no vehicle speed is detected at start off.
^ DTC 72 will set when vehicle speed has been detected and is lost.