RAM 1500 Truck 2WD V6-3.9L VIN X (1999)
PROVIDED IN HE SERVICE PACKAGE OR SPECIFIED IN THE CHRYSLER MOPAR PARTS CATALOG.
Seat Belt Control Timer Module
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.
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.
The SCTM cannot be repaired. If faulty or damaged, it must be replaced.
Seat Belt Control System Test Mode
The structural seat belt control system has a test mode feature. This feature allows the seat belt control system to be tested from proper operation while
the vehicle is stationary by overriding the normal Seat Belt Control Timer Module (SCTM) control functions. The seat belt system and the airbag
system must be tested for proper operation following the service of any seat belt control system or airbag system component. See Airbag Systems for
more information on testing of the airbag system. This test mode will confirm the following:
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Both door jamb switches and their input circuits to the SCTM are functional.
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The fused B(+), fused ignition switch output (RUN/ACC), and ground circuits to the SCTM are functional.
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The SCTM fault circuit to the Airbag Control Module (ACM), the ACM, the Chrysler Collision Detection (CCD) data bus, and the seat belt
reminder lamp in the instrument cluster are functional.
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Both seat belt retractor latch solenoids and their circuits are functional and can be activated by the SCTM.
To initiate the structural seat belt control system test mode, proceed as follows:
1. If the structural seat belt controls system test mode has not been performed previously within the past 72 hours, reset the SCTM by removing the
Ignition-Off Draw (IOD) fuse from the junction block, the reinstalling it. (Ignition must be OFF).
2. Sit in the driver side front seat of the vehicle and close all doors.
3. Push in the cigar lighter, turn the windshield wipers on "HIGH".
4. Within five seconds the ignition switch must be cycled On, Off, On, Off, On, Off, and then finally back to On position. Leave the ignition switch
in the On position for the remainder of this procedure. This action enters the seat belt control system into its test mode for a maximum of five
minutes. After five minutes, the seat belt control system will automatically return to its normal operating mode.
5. The seat belt reminder lamp should light shortly after entering the test mode to confirm that the seat belt control system is in the test mode, and
that the seat belt control system fault circuit is functional. If the lamp fails to light, use a DRB scan tool and the proper Diagnostic Procedures to
diagnose the SCTM fault circuit to the ACM, the ACM, and the CCD data bus.
6. Open the driver side front door. Check that both the passenger and driver side outboard front seat belt retractors are unlatched by slowly pulling
the seat belt webbing out of the retractor. If only one retractor is unlatched, the latched retractor and circuit must be diagnosed. See Seat Belt
Control System in the appropriate service manual for more information. If both retractors are latched, see Seat Belt Control Timer Module in the
Diagnosis and Testing.
