Supplemental Restraint Sensing and Diagnostic Module

The supplemental restraint sensing and diagnostic module (SDM) performs the following functions in the SRS:

The SDM connects to the SRS wiring harness using a 12-way connector. The SDM harness connector uses a shorting bar across certain terminals in the contact area. Removal of the SDM Connector Position Assurance (CPA) or the harness connector itself will connect the AIR BAG warning lamp to ground through the shorting bar.

The AIR BAG warning lamp will come ON steady with power applied to the SDM when either one of the following two conditions exist:

The SDM receives power whenever the ignition switch is in the RUN or START positions.

AIR BAG Warning Lamp

The ignition switch applies ignition voltage to the AIR BAG warning lamp. The AIR BAG warning lamp receives power whenever the ignition switch is at the RUN or START positions. The supplemental restraint sensing and diagnostic module (SDM) controls the lamp by providing ground with a lamp driver. The SRS uses the AIR BAG warning lamp to do the following:

The AIR BAG warning lamp is the key to driver notification of SRS malfunctions. Refer to Diagnostic System Check - SRS for proper lamp operation.

The AIR BAG warning lamp is two light emitting diodes (LED). The LEDs are not serviceable. Refer to Instrument Cluster Replacement in Instrument Panel And Gauges for replacement of the Instrument Cluster.

Supplemental Restraint Steering Wheel Module Coil

The supplemental restraint steering wheel module coil consists of two or more current-carrying coils. The supplemental restraint steering wheel module coil attaches to the steering column. Two of the current-carrying coils allow rotation of the steering wheel while maintaining continuous contact of the driver deployment loop to the supplemental restraint steering wheel module.

There is a shorting bar on the yellow 2-way connector near the base of the steering column that connects the supplemental restraint steering wheel module coil to the SRS wiring harness. The shorting bar shorts the circuits to the supplemental restraint steering wheel module coil and supplemental restraint steering wheel module during the disconnection of the yellow 2-way connector. The shorting of the supplemental restraint steering wheel module coil and supplemental restraint steering wheel module circuitry will help prevent unwanted deployment of the air bag when servicing the steering column or other SRS components.

Inflator Modules

The inflator modules consist of an supplemental bag and an inflator. An inflator consists of a canister of gas-generating material and an initiating device. The initiator is part of the deployment loop. When the vehicle is in a frontal crash of sufficient force, the supplemental restraint sensing and diagnostic module (SDM) causes current to flow through the deployment loops. Current passing through the initiator ignites the material in the inflator module. The gas produced from this reaction rapidly inflates the air bag.

There is a shorting bar on the supplemental restraint steering wheel module side of the upper steering column connector that connects the supplemental restraint steering wheel module coil to the supplemental restraint steering wheel module. The shorting bar shorts across the supplemental restraint steering wheel module circuits during the disconnection of the upper steering column connector. The shorting of the supplemental restraint steering wheel module circuitry will help prevent unwanted deployment of the air bag when servicing the supplemental restraint steering wheel module, the steering column or other SRS components.

There is a shorting bar on the supplemental restraint IP module connector that connects to the SRS wiring harness. The shorting bar shorts across the supplemental restraint IP module circuits during the disconnection of the supplemental restraint IP module connector. The shorting of the supplemental restraint IP module circuitry will help prevent unwanted deployment of the air bag when servicing the supplemental restraint IP module, the instrument panel or other SRS components.

In the event of a fault in the supplemental restraint IP module switch circuitry, the SDM will detect the fault and set Diagnostic Trouble Code (DTC) B1054, the SDM will attempt to illuminate the AIR-BAG OFF lamp, the AIR BAG warning lamp will turn ON and the supplemental restraint IP module will default to the suppressed (disabled) state.

Supplemental Restraint IP Module Switch (Pickup and Extended Cab Only)

The supplemental restraint IP module switch is a manual two-position key switch located in the instrument panel, to the right of the steering wheel. This switch gives the vehicle operator the ability to enable or disable supplemental restraint IP module (passenger front air bag) deployment should the vehicle be involved in a severe frontal collision. The vehicle operator may choose to disable the supplemental restraint IP module if there is no occupant in the front seat, or if there is a child in a rear-facing child seat in the front seat.

The manual key-switch operates in two positions. When the key is vertical, the switch is in the OFF position and the supplemental restraint IP module is in the suppressed (disabled) state. In the suppressed state, the supplemental restraint IP module will not deploy in the event of a severe frontal collision. When the key is horizontal, the switch is in the ON position and the supplemental restraint IP module is in the nonsuppressed (enabled) state. In the nonsuppressed state, the supplemental restraint IP module will deploy in the event of a severe frontal collision. The key--switch assembly also includes a backlit switch cover which illuminates when the headlights are on.

The IP module switch is directly interfaced to the supplemental restraint sensing and diagnostic module (SDM). The SDM senses the state of the IP Module switch. When the switch is in the ON position, the SDM enables possible deployment of the supplemental restraint IP module. When the switch is in the OFF position, the SDM disables or inhibits possible deployment of the supplemental restraint IP module.

Supplemental Restraint Front End Discriminating Sensor

The presence of an supplemental restraint front end discriminating sensor enhances the SRS performance. Use of the supplemental restraint front end discriminating sensor provides timely deployment of the air bags during some crashes. Although this is a mechanical sensor, the sensor is not a part of the deployment loop but instead only provides an input signal to the supplemental restraint sensing and diagnostic module (SDM).

Steering Column

The steering column is energy absorbing. The steering column may compress during a frontal crash in order to decrease the chance of injury to the driver.

Knee Bolster

The knee bolsters absorb energy and control the forward movement of the vehicle's front seat occupants during a frontal crash, by limiting leg movement.

Definitions

Air Bag: An inflatable cloth cushion designed to deploy in certain frontal crashes. The air bags distribute the impact load more evenly over the occupant's head and torso in order to supplement the safety belt protection.

Asynchronous: An event that can occur at any time without a warning and without falling within a defined time period.

B+: The battery voltage available at the time of the indicated measurement. With the ignition switch in the RUN position and the engine stopped, the voltage is usually 11.5 -12.5 V. With the engine at idle, the voltage may be 14.0 -16.0 V. During engine cranking, the voltage can be as low as 10.0 V.

Bulb Test: The supplemental restraint sensing and diagnostic module (SDM) will cause the air bag warning indicator to flash 7 times. Under normal operation, this occurs when the ignition is turned from the OFF position to the RUN position. The bulb test will also occur if the IGNITION 1 voltage exceeds 17.1 V and then returns within the normal operating voltage range. A malfunction could prevent the module from flashing the indicator.

Continuous Monitoring Test: The supplemental restraint sensing and diagnostic module (SDM) continuously monitors the Supplemental Restraint System during each 100 millisecond interval. The IGNITION 1 voltage at the module must be with the normal operating voltage range for the continuous monitoring to occur. These tests follow the power-on tests.

Data Link Connector (DLC): The DLC electrically connects to many on-board computers and allows communication with an off-board computer such as a scan tool.

Datum Line: A base line parallel to the plane of the vehicle underbody or the frame. All vertical measurements originate from this base line.

Deploy: To inflate the air bag.

Deployment Loop Continuity Test: The supplemental restraint sensing and diagnostic module (SDM) performs this test in order to inspect for voltage variations in the DRIVER SIDE HIGH/LOW and the PASSENGER SIDE HIGH/LOW circuitry. The module first measures the IGNITION 1 and the 23 VLR in order to verify that the voltage is within specifications. The module then performs the deployment loop continuity test. Detection of a malfunction during these tests may prevent the resistance measurement test from occurring until the next ignition cycle. This test is part of the power-on tests and occurs before the continuous monitoring tests.

Deployment Loops: The circuits that supply the current to the inflator modules for air bag deployment.

Diagnostic Trouble Code (DTC): An alphanumeric designator used by the supplemental restraint sensing and diagnostic module (SDM) in order to indicate specific SRS malfunctions.

Driver Current Sink: An output of the supplemental restraint sensing and diagnostic module (SDM) that supplies a low resistance path to ground for the supplemental restraint steering wheel module circuit.

Driver Current Source: An output of the supplemental restraint sensing and diagnostic module (SDM) that supplies current into the supplemental restraint steering wheel module circuit.

EEPROM (Electrically Erasable Programmable Read Only Memory) : Memory that does not require power to the supplemental restraint sensing and diagnostic module (SDM) in order to retain its contents.

Higher Priority Fault: Each DTC has an assigned priority based on its detectability with other DTCs present. The priority corresponds to the detectability of the malfunction only. This does not relate to the seriousness of the malfunction with respect to deployment or non deployment under any given condition.

Ignition Cycle: The operation of the ignition switch causes this cycle to occur. The supplemental restraint sensing and diagnostic module (SDM) must first sense IGNITION 1 input greater than 8.2 V with the ignition switch in the RUN position. The IGNITION 1 input voltage must remain above 8.2 V for at least 10 seconds before turning the ignition switch to the OFF position.

Ignition 1: A B+ circuit receiving power with the ignition in the RUN position or the START position.

Initiator: Located in the inflator module, the initiator initiates the chemical reaction that inflates the air bag when sufficient current flows through the component.

Normal Operating Voltage Range: 8.2-17.1 V when measuring between the supplemental restraint sensing and diagnostic module (SDM) IGNITION 1 terminal to ground.

Passenger Current Sink: An output of the supplemental restraint sensing and diagnostic module (SDM) that supplies a low resistance path to ground for the supplemental restraint IP module circuit.

Passenger Current Source: An output of the supplemental restraint sensing and diagnostic module (SDM) that supplies current into the supplemental restraint IP module circuit.

Power-on Test: Tests that the supplemental restraint sensing and diagnostic module (SDM) performs on the Supplemental Restraint System once per ignition cycle. These tests occur immediately after the module receives IGNITION 1 voltage, and before the continuous monitoring tests.

Resistance Measurement Test : A test that the supplemental restraint sensing and diagnostic module (SDM) performs once per ignition cycle in order to measure the resistance of the deployment loops. The module first measures IGNITION 1, 23 VLR, and the deployment loop voltages in order to verify readings within specifications. The module then sources a constant current into the loop. The module measures the voltage drop across the loop and converts the value to a resistance value. This resistance value is within the range of 0.0 - 6.3 ohms. Upon the detection of an open circuit, the module aborts the tests in order to prevent the calculation of the resistances until the next ignition cycle. This test also inspects for proper operation of the driver/passenger current sources. This test is part of the power-on tests and occurs before the continuous monitoring tests.

Scan Tool: An off-board computer that reads on-board computer diagnostic information through the use of a DLC.

Serial Data: The information communicated to an off-board computer using the DLC. Some of this data represents the status of the Supplemental Restraint System.

SRS: Supplemental Restraint System.

SRS Wiring Harness: The wires and connectors that electrically connect the components in the SRS.

Supplemental Restraint Front End Discriminating Sensor: A sensor mounted on the front of the vehicle that supplies an input signal to the supplemental restraint sensing and diagnostic module (SDM).

Supplemental Restraint IP Module: An assembly located on the right of the IP consisting of an inflatable air bag, an inflator, and an initiator.

Supplemental Restraint IP Module Switch: A manual two-position key switch located in the instrument panel, to the right of the steering wheel. This switch gives the vehicle operator the ability to enable or disable supplemental restraint IP module (Passenger Front Air Bag) deployment should the vehicle be involved in a severe frontal collision. The vehicle operator may choose to disable the supplemental restraint IP module if there is no occupant in the front seat, or if there is a child in a rear-facing child seat in the front seat.

Supplemental Restraint Sensing and Diagnostic Module: The SDM that provides reserve energy to the deployment loops, deploys the air bags when required, and performs diagnostic monitoring of all SRS components.

Supplemental Restraint Steering Wheel Module: An assembly located in the steering wheel hub consisting of an inflatable bag, an inflator, and an initiator.

Supplemental Restraint Steering Wheel Module Coil: An assembly of two or more current carrying coils mounted within the steering column hub. The assembly allows the rotation of the steering wheel while maintaining continuous electrical circuit contact. Two of the coils provide continuous contact of the driver deployment loop to the supplemental restraint steering wheel module.

23 VLR: The 23 volt loop reserve. The energy supply that is internal to the supplemental restraint sensing and diagnostic module (SDM).