I attached the diagram as you requested.
Does the speedometer work all the time? If the speed sensor was the issue, the speedometer would fall out at times.
Make sure the connector at the speed sensor is clean and tight.
I attached the flow chart for you as well. The VSS does control shift points and could be the actual issue.
The Vehicle Speed Sensor (VSS) system is a pulse generator consisting of a speed sensor assembly, located in the case extension, and a toothed vehicle speed sensor reluctor wheel, which is pressed onto the final drive carrier assembly. As the vehicle drives forward, the vehicle speed sensor reluctor wheel rotates. This rotation produces a variable AC signal in the pickup coil that is proportional to vehicle speed. The PCM uses this signal in order to calculate vehicle speed, shift timing and gear ratios.
If the PCM detects a low vehicle speed with a high engine speed while in a drive range, then DTC P0502 sets. DTC P0502 is a type B DTC.
Conditions for Running the DTC
No MAP sensor DTC P0107 or P0108.
No TP sensor DTC P0121, P0122 or P0123.
No AT ISS DTC P0716 or P0717.
The TP angle is 12% or greater.
The engine torque is 95 - 407 Nm (70 - 300 ft. lbs.).
The input shaft speed is 1,500 RPM or greater.
Conditions for Setting the DTC
The output shaft speed is less than 150 RPM for 2.5 seconds.
Action Taken When the DTC Sets
The PCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
The PCM commands maximum line pressure.
The PCM freezes transmission adaptive functions.
The PCM calculates vehicle speed from the AT input shaft speed sensor for shift timing.
The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
The PCM stores DTC P0502 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.
Conditions for Clearing the MIL/DTC
The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
A scan tool can clear the MIL/DTC.
The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM.
The numbers refer to the step numbers on the diagnostic table.
3. This step tests the ability of the VSS to produce an AC voltage. This step also verifies the integrity of the wiring to the PCM.
4. This step tests the VSS circuit for correct resistance.
Images (Click to enlarge)
Sunday, September 27th, 2020 AT 12:53 PM