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Seat Belt Control Timer Module


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 rear 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 seat 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 de-energized 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 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 sense 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 an input indicating a change in the state of a monitored switch has occurred, the 30 minutes times 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. See Seat Belt Reminder Lamp in the Description and Operation section of Group 8E - Instrument Panel Systems in the Service Manual for more information.

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 in this group for more information on testing of the airbag system. This test mode will confirm the following:
- Both door jamb switches and they're input circuits to the SCTM are functional.
- The fused B (+), fused ignition switch output (run/acc), and ground circuits to the SCTM are functional.
- 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.
- 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 at follows:


1. If the structural seat belt controls system test mode has not been performed previously within the past 72 hours, reset the SCTM be removing the Ignition-Off Draw (IOD) fuse from the junction block, then reinstalling it.

2. Sit in the driver side front seat of the vehicle and close all doors.

3. Push in the cigar lighter.

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 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 manual 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 group 8M for more information. If both retractors are latched, see Seat Belt Control Timer Module in the Diagnosis and Testing section of this group.


7. Close the drive side from door. Check that both the passenger and driver side outboard front seat belt retractors are latched by slowly pulling the seat belt webbing out of the retractor. If only one retractor is latched, the unlatched retractor and circuit must be diagnosed. See Seat Belt Retractor Latch Solenoid in the Diagnosis and Testing section of this group. If both retractors are unlatched, see Seat Belt Control Timer Module in the Diagnosis and Testing section of this group.

8. Repeat steps #6 and #7, but open and close the passenger side front door instead of the driver side.
9. Turn the ignition switch to the Off position. This will cause the seat belt control system to exit its test mode and return to normal operation.
10. Turn the ignition switch back to the On position. The seat belt reminder and airbag indicator lamps should turn off shortly after their normal display functions (about six and seven seconds, respectively). If either lamp remains lighted, use a DRB scan tool and the proper Diagnostic Procedures manual to diagnose the SCTM fault circuit to the ACM, the airbag system, the ACM, and the CCD data bus.
11. If the seat belt control system test mode has timed out prior to completion of the tests (about five minutes after the test was initiated), go back to step #2.

The SCTM is programmed to consider certain parameters as an indication of a faulty Gravity (G)-sensor. In some peculiar vehicle use situations these parameters may be exceeded, causing the seat belt reminder lamp to illuminate indicating an SCTM fault, and then extinguish for no apparent reason. The following parameters should be considered if an intermittent seat belt reminder lamp illumination complaint is being diagnosed, and the test mode reveals no problems with the structural seat belt control system operation.

- If the SCTM monitors ten ignition cycles without input from the G-sensor indicating that the vehicle has accelerated or decelerated sufficiently to require the seat belts to be latched. An ignition cycle is defined as: The ignition switch turned to the On position for at least thirty minutes, followed by the ignition switch being turned to the Off position. The SCTM considers this a G-sensor fault because it would normally be expected that the seat belts would require latching at some point while driving, within ten ignition cycles. The SCTM will discontinue the fault signal and reset the ignition cycle counter to zero as soon as it sees a "normal" G-sensor input.

- If the SCTM monitors that the G-sensor input has required the seat belts to remain latched for more that about four seconds. This condition could occur if the vehicle is parted on a steep grade with the ignition switch in the On position, and is considered a G-sensor fault by the SCTM because the duration of the G-sensor input requiring the seat belts to be latched should not normally exceed four seconds. The SCTM will discontinue the fault signal as soon as it sees a "normal" G-sensor input
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