Speedometer Module: Description and Operation

DESCRIPTION:
The programmable speedometer/odometer module (PSOM) receives input from the rear brake anti-lock sensor, which is mounted on the rear axle differential housing. The PSOM processes this input signal information and relays it to the powertrain control module and the speed control module. This signal tells the powertrain control module the vehicle speed in miles per hour (mph). The PSOM is also used as an input in determining shift scheduling and electronic pressure control.

SYMPTOMS:
Harsh engagements, firm shift feel, abnormal shift schedule, unexpected downshifts may occur at closed throttle. Torque converter clutch will not engage, elevated EPC pressures.

NOTE: EPC shorted to ground or failed low may result in a false VSS code. Diagnose EPC concerns first. Then recheck VSS input and PSOM.

DIAGNOSTIC TROUBLE CODES:
P0500, P1500, P1501.