Grand Cherokee 2WD V6-3.7L (2008)
Memory Positioning Module: Description and Operation
Memory Seat Module - Operation
OPERATION
The Memory Seat Module (MSM) receives battery current through a 25 amp circuit breaker in the Power Distribution Center (PDC) so that the memory
system remains operational, regardless of the ignition switch position. When the driver memory switch button is pushed, a resistance signal is sent to the
MSM via the Controller Area Network (CAN) bus circuit. The MSM is responsible for the 12v battery feed and ground path to the power seat adjuster
motor and other memory system components.
The MSM receives memory set/position switch input through the CAN bus circuit. The MSM also receives hard wired input from the hall effect sensors,
mounted on each of the driver power seat adjuster motors and the driver side view mirror motor. The programmed software in the module allows it to
know where the seat and adjustable pedals are located in its designed travel by a pulse count generated from the hall effect sensors. This way, when the
memory switch is depressed the module will power these components until the correct preset location is achieved. The module will prevent the seat
memory recall function from being initiated, if the transmission gear selector lever is not in the Park position, or if the vehicle is moving. These inputs
are monitored over the Controller Area Network (CAN) bus circuit by the MSM.
A memory setting is saved by pressing the "set" button, then pressing either the memory "1" or "2" button within 5 seconds of pressing the "set" button.
A memory setting is recalled by pressing either the memory "1" or "2" button, or by pressing the unlock button on a "linked" Remote Keyless Entry
(RKE) transmitter.
For driver safety, memorized settings can not be recalled if the transmission is in a position other than Park or the seat belt is latched.
The MSM performs the following functions:
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Positions the driver power seat (vertical, horizontal, and recliner positions).
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Positions the power adjustable pedals.
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Sends the memory save or recall (number 1 or number 2) command over the CAN data bus circuit to the other memory system components, radio
station pre-sets and power mirror positions.
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Provides for "linking" the key FOBs to memory.
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Provides for the easy entry/exit feature.
When a memory button is pressed (number 1 or number 2) on the memory switch, the Driver Door Module (DDM) sends a recall message to the MSM.
The MSM will then position the memory system components to the preprogrammed location/setting. When the Remote Keyless Entry (RKE) Transmitter
button is pressed, depending on which transmitter (number 1 or number 2), the SKREEM (RKE Receiver) sends the recall request and FOB number
(number 1 or number 2) data message. This RKE transmitter function depends on if the MSM is programmed to trigger the recall (linked FOBs).
A key FOB is "linked" to a memory setting by pressing the "set" button and then pressing either the memory "1" or "2" button within 5 seconds of
pressing the set button, then by pressing the "lock" button on the selected key FOB.
The memory system "Easy Entry and /Exit" feature provides the driver with more room to enter or exit the vehicle. When the seat is in a memorized
position, it will move rearward 55 millimeters or to the end of its travel, whichever occurs first, when the key is removed from the ignition switch lock
cylinder. This is a customer programmable feature of the overhead console. The seat will return to the memory position when the driver turns the
vehicle's ignition switch out of the LOCK position.
The memory system "learns" the seat and adjustable pedal motor maximum end positions when the motor reaches the limit of travel in any direction and
stalls. Subsequently, movement will stop just short of that position to avoid extra stress on the motors and mechanisms. If the system learned a maximum
position as a result of an obstruction, as for instance if a large object was placed on the floor behind the seat, the system can relearn the "true" maximum
position through manually operating the power seat after the obstruction is removed.
NOTE: It is normal for the power accessories contained in the memory system to stop at the maximum "learned" position and then continue to
the "true" maximum position when the control switch is released and then applied in the same direction a second time.
Certain functions and features of the memory system rely upon resources shared with other electronic modules in the vehicle over the Controller Area
Network (CAN) bus. The CAN bus allows the sharing of sensor information. This helps to reduce wire harness complexity, internal controller hardware,
and component sensor current loads. At the same time, this system provides increased reliability, enhanced diagnostics, and allows the addition of many
new feature capabilities. For diagnosis of these electronic modules or of the CAN bus, the use of a scan tool and the proper diagnostic information are
needed.
