Shift Lever Position (SLP)

The TCM identifies the position of the manual lever by comparing the current switch positions of the Transmission Range Sensor (TRS). This is accomplished by logic circuitry within the TCM.

The primary function of SLP logic is to provide safe, continuous, but limited operation of the transaxle with the presence of an invalid or transition input code. The SLP logic function screens the input codes from the switches and provides an SLP output signal to control actual gear selection.

Inputs include the codes indicated by the TRS current shift lever position, pressure switch indications and speed ratio data from the input to most of the other functions in the TCM.

The identified position is stored in memory. The current switch position is determined by sensing the voltage changes that occur at the corresponding TCM pin terminals for the switches. The TCM receives the switch signal and processes the data. On vehicles with a BCM, the TCM sends the Shift Lever Position information to the BCM and the cluster electronic PRNDL display via the CCD Bus. The cluster electronic PRNDL display illuminates the appropriate shifter position indicator on the instrument cluster. For vehicles without a BCM, the shifter position indicator is cable-operated.

CAUTION: AN INCORRECT INPUT (FOR EXAMPLE, A DEFECTIVE SWITCH) OF ONE OF THESE POSITIONS COULD, WITH SUFFICIENT TIME, RESULT IN EITHER A PRESSURE SWITCH OR SPEED CHECK FAULT, WHEN IN FACT THE REAL CAUSE IS A TRS FAULT. THIS TYPE OF FAULT CAN OCCUR, FOR EXAMPLE, WHEN THE MANUAL VALVE PORTING IS IN REVERSE BUT THE CODE IS INDICATING "OD." IN THIS CASE, THE LOW/REVERSE PRESSURE SWITCH DATA AND INPUT SPEED DATA WILL NOT AGREE WITH THE EXPECTED RESULTS FOR SHIFT LEVER POSITION = "OD" THEREFORE, IT IS IMPORTANT TO PERFORM A SHIFT LEVER POSITION TEST WITH THE DRBIII SCAN TOOL BEFORE DIAGNOSING ANY TROUBLE CODES.

It is extremely important that accurate shift lever position data be available to the TCM. The accuracy of any diagnostic trouble code found in memory is doubtful unless the Shift Lever Test, performed on the DRBIII Scan Tool, passes without fail.