Chevrolet Silverado / GMC Sierra. Service manual — part 702

produced from this reaction rapidly inflates the air bag. Once the air bag is inflated it quickly
deflates through the air bag vent holes.

Each dual stage inflator module is equipped with a shorting bar located on the connectors of the
module. The shorting bar shorts the inflator module deployment loop circuitry to prevent
unwanted deployment of the air bag when it is disconnected.

Inflatable Restraint Steering Wheel Module Coil

The steering wheel module coil is attached to the steering column and is located under the
steering wheel. The steering wheel module coil consists of 2 or more current-carrying coils. The
coils allow the rotation of the steering wheel while maintaining continuous electrical contact
between the driver deployment loop and the steering wheel module. Four coil wires are used for
the steering wheel module deployment loop. Additional coil wires are used for accessories
attached to the steering wheel depending on the vehicle model. The steering wheel module coil
connector is located near the base of the steering column. The connector contains a shorting bar
that shorts the steering wheel module coil deployment loop circuitry to prevent unwanted
deployment of the air bag when it is disconnected.

Inflatable Restraint Front End Sensors

The front end sensors are equipped on vehicles to supplement the Supplemental Inflatable
Restraint (SIR) System performance. The front end sensors are electronic and are not part of the
deployment loops, but instead provide inputs to the sensing and diagnostic module (SDM). The
front end sensors can assist in determining the severity of some frontal collisions. The SDM uses
the input from the front end sensors to assist in determining the severity of a frontal collision
further supporting air bag deployment. If the SDM determines a deployment is warranted, the
SDM will cause current to flow through the deployment loops deploying the frontal air bags.

Inflatable Restraint Side Impact Sensor (SIS)

The side impact sensor (SIS) contains a sensing device which monitors vehicle acceleration and
velocity changes to detect side collisions that are sever enough to warrant side SIR deployment.
The SIS is not part of the deployment loop, but instead provides an input to the SDM. The SDM
contains a microprocessor that performs calculations using the measured accelerations and
compares these calculations to a value stored in memory.

Inflatable Restraint Wiring Harnesses

The wiring harnesses connect the sensing and diagnostic module (SDM), inflator modules,
Passenger Presence System (PPS), front end sensors, seat position sensors (SPS), passenger seat
belt tension retractor sensor, rollover sensor, side impact sensors and the serial data circuit

2008 Chevrolet Silverado 1500

2008 RESTRAINTS Supplemental Inflatable Restraints - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

together using connectors. SIR deployment loop connectors are yellow in color for easy
identification. When repairing Supplemental Inflatable Restraint (SIR) System wiring harnesses,
follow the proper testing and wiring repair procedures outlined in this manual.

Seat Belt Pretensioner

The seat belt pretensioner consist of a housing, a seat belt retractor, the seat belt webbing, an
initiator, and a canister of gas generating materials. The initiator is part of the seat belt
pretensioner deployment loop. When the vehicle is involved in a collision of sufficient force, the
sensing and diagnostic module (SDM) causes current to flow through the seat belt deployment
loops to the initiator. Current passing through the initiator ignites the material in the canister
producing a rapid generation of gas. The gas produced from this reaction deploys the seat belt
pretensioner and retracts the seat belt webbing, which removes all of the slack in the seat belts.
Depending on the severity of the collision, the seat belt pretensioner may deploy without the
frontal inflator modules deploying, or they will deploy immediately before the frontal inflator
modules deploy. Each seat belt pretensioner is equipped with a shorting bar that is located in the
connector of the seat belt pretensioner. The shorting bar shorts the seat belt pretensioner circuitry
to prevent unwanted deployment of the seat belt pretensioner when the connector is disconnected.

Steering Wheel and Column

The steering wheel and column are designed to absorb energy when driver contact is made with
the steering wheel or inflated air bag. In a frontal collision the driver may contact the steering
wheel directly or load the steering wheel and column through the inflated air bag. When the
driver applies load to the air bag or steering wheel the column will compress downward
absorbing some of the impact, helping to reduce bodily injuries to the driver. The steering wheel
and column must be inspected for damage after a collision.

Driver and Passenger Knee Bolsters

The knee bolsters are designed to help restrain the lower torsos of front seat occupants by
absorbing energy through the front seat occupants upper legs. In a frontal collision the front seat
occupants legs may come in contact with the knee bolsters. The knee bolsters are designed to
crush or deform absorbing some of the impact, which helps to reduce bodily injuries. The driver
and passenger knee bolsters are located in the lower part of the instrument panel and must be
inspected for damage after a collision.

2008 Chevrolet Silverado 1500

2008 RESTRAINTS Supplemental Inflatable Restraints - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

2008 BRAKES

Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

SPECIFICATIONS

FASTENER TIGHTENING SPECIFICATIONS

Fastener Tightening Specifications

SCHEMATIC AND ROUTING DIAGRAMS

ANTILOCK BRAKE SYSTEM SCHEMATICS

Application

Specification

Metric

English

Brake Pipe Fittings

18 N.m

13 lb ft

BPMV Bracket Bolts

22 N.m

16 lb ft

BPMV Mounting Bolt (JH6, JH7)

11 N.m

97 lb in

BPMV Mounting Nuts (JD9, JF3, JF7)

9 N.m

80 lb in

EBCM to BPMV Screws

3 N.m

27 lb in

Wheel Speed Sensor Bolt - Front

17 N.m

13 lb ft

Wheel Speed Sensor Bolt - Rear

9 N.m

80 lb in

Yaw Rate Sensor/Lateral Accelerometer Nut

7 N.m

62 lb in

2008 Chevrolet Silverado 1500

2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

2008 Chevrolet Silverado 1500

2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Fig. 1: Module Power, Ground, Serial Data, Pump Motor and Brake Switch (JL4)
Courtesy of GENERAL MOTORS CORP.

2008 Chevrolet Silverado 1500

2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado