Powertrain Controls - ECM/PCM

DTC 24 Speed Sensor Circuit Low - (Trans Output Signal):

Buffer Module And Speed Sensor Circuit Wiring:

CIRCUIT DESCRIPTION
The speed sensor circuit consists of a magnetic induction type sensor, a Vehicle Speed Sensor (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 Powertrain Control Module (PCM).

DIAGNOSTIC TROUBLE CODE (DTC) 24 WILL SET WHEN
^ Not in Park/Neutral (P/N).
^ CKT 437 voltage is constant.
^ Engine speed is greater than 3000 RPM.
^ Output speed is less than 250 RPM.
^ Manifold Absolute Pressure (MAP) is less than 100 kPa (29.5 in of Hg)
^ Throttle Position (TP) is between 10% and 100%.
^ All conditions met for 3 seconds.
^ No DTC(s) 21, 22, 28, 33, or 34.

ACTION TAKEN (PCM WILL DEFAULT TO)
Second gear only at maximum line pressure.

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 chart:

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 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.