Grand Cherokee 2WD V8-5.7L VIN 2 (2005)
Shifter A/T: Description and Operation
NAG1 Automatic Transmission
MECHANISM-SHIFT
DESCRIPTION
The automatic transmission is operated with the help of a Shift Lever Assembly (SLA) (1) located in the floor console. There are four positions to
which the selection lever can be shifted: P, R, N, D. In addition, the selector lever can be moved sideways (±) in position "D" to adjust the shift range.
All selector lever positions, as well as selected shift ranges in position "D", are identified by the SLA. The information is then sent to the Transmission
Control Module (TCM) via a hardwire connection. At the same time, the selector lever positions "P", "R", "N" and "D" are transmitted by a shift
cable to the selector shaft in the transmission.
The SLA is comprised of the following functions:
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Key lock: Depending on the selector lever position, the ignition cylinder is locked/unlocked, i.e., the ignition key can be removed only if the
selector lever is in position "P". A park lock cable is used to perform this function.
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Park lock: The selector lever is not released from position "P" until the brake pedal has been applied and the ignition key is in "ACC" or ON"
positions. Shift lock is controlled by the brake light switch in conjunction with a locking solenoid in the SLA. As soon as the brake pedal is applied
firmly, the locking solenoid is de-energized to unlock the selector lever.
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Reverse inhibitor: As soon as the vehicle speed exceeds approximately 4 - 7 mph, it is no longer possible to move the selector lever from position
"N" to position "R". The reverse inhibit functionality is controlled by the TCM and the same solenoid as the park lock. As the vehicle accelerates
past the calibrated speed threshold, the solenoid is energized to block the motion of the shift lever necessary to move from NEUTRAL to
REVERSE. The reverse inhibit is not released until the vehicle speed falls below approximately 4-7 mph and the shifter is moved out of the "D"
shifter position.
OPERATION
With the selector lever in position "D", the Transmission Control Module (TCM) automatically shifts the gears that are best-suited to the current
operating situation. This means that shifting of gears is continuously adjusted to current driving and operating conditions in line with the selected shift
range and the accelerator pedal position. Starting off is always performed in 1st gear.
