RAM 1500 Truck 4WD V8-5.9L VIN Z LDC (1999)
Seat Belt Control Module: Description and Operation
SEAT BELT CONTROL TIMER MODULE
DESCRIPTION
The Seat Belt Control Timer Module (SCTM) is secured to a bracket underneath the front edge of the front seat center cushion. The SCTM
mounting bracket also serves as the support for the slide-out seat cup holder unit. The SCTM controls the supply of battery current to both of the
front seat belt retractor latch solenoids. The SCTM contains an electromechanical Gravity (G)-sensor and an electronic timer circuit. The SCTM
monitors the ignition switch state and both door jamb switches through hard-wired inputs. In response to those inputs, the SCTM controls
hard-wired outputs to both seat belt retractor latch solenoids. The SCTM also sends diagnostic outputs to the Airbag Control Module (ACM) over
a hard-wired fault circuit.
For diagnosis of the CCD data bus, the ACM or the fault circuit input to the ACM from the SCTM, the use of a DRB scan tool and the proper
Diagnostic Procedures are recommended. The SCTM cannot be repaired. If faulty or damaged, it must be replaced.
OPERATION
The SCTM provides battery current to energize the seat belt retractor latch solenoids whenever the ignition switch is in the ON or ACCESSORY
position, unless the G-sensor input indicates a vehicle condition that requires the set belt retractor to be latched. When the seat belt retractor latch
solenoids are energized the retractor spools are unlatched, and the seat belt webbing can be extracted from the retractor. When the solenoids are
deenergized the retractor spools latch, preventing the seat belt webbing from being extracted further from the retractor. This logic ensures that the
seat belts will latch and/or remain latched if battery power is lost during a vehicle collision.
The electromechanical G-sensor within the SCTM monitors the rate of vehicle acceleration and de-acceleration in any horizontal direction. The
G-sensor also responds to the horizontal attitude of the vehicle, If the G-sensor monitors a gravity force of greater than about 0.7G in any
horizontal direction, or the vehicle is tilted in any direction at an angle of greater than about 45 degrees, the SCTM will de-energize (lock) the seat
belt retractor latch solenoids.
The SCTM electronic timer circuit provides the vehicle occupants with the ability to extract the seat belt webbing from the retractor spool for a
time period of about 30 minutes after the ignition switch is turned to the Off position. The electronic timer circuit also monitors the state of the
door jamb switches, and unlatches the seat belt retractors after either door jamb switch cycles from open to closed or from closed to open. Each
time the SCTM receives and input indicating a change in the state of a monitored switch, the 30 minute unlatch timer starts again. The timer also
is used to de-energize the retractor latch solenoids after about 30 minutes, and prevent the battery from being drained while the vehicle is not
being driven.
The hard wired SCTM output to the ACM is used to indicate whether a fault condition is present in the structural seat belt control system. The
ACM monitors the input from the SCTM and sends the proper messages to the instrument cluster on the Chrysler Collision Detection (CCD) data
bus to turn the seat belt reminder lamp ON or OFF. If the ACM receives a fault input or does not detect any input from the SCTM, it sets a fault
code and sends messages to the instrument cluster to turn the lamp on.
