Technician
Reference
Booklet
SUPPLEMENTAL
RESTRAINT SYSTEM (SRS)
Module 604

MSA5P0136C
June 2013

This Technical Reference Booklet (TRB) is designed to be used in a classroom
environment or as a guide for self study.
The TRB is not intended to be used as a supplement or substitute for the
Subaru Service Manual. Always consult the appropriate Service Manual
when performing any diagnostics, maintenance or repair to any Subaru
vehicle.

© Copyright 2013
Subaru of America, Inc.

All rights reserved. This book may not be
reproduced in whole or in part without the
express permission of Subaru of America,
Inc. Specifications in this Guide are based
on the latest product information available at
the time of publication. Some images shown
are for illustration purposes only.
Subaru of America, Inc. reserves the right at
any time to make changes or modifications
to systems, procedures, descriptions, and
illustrations contained in this book without
necessarily updating this document.
Information contained herein is considered
current as of June 2013.

SRS Disclaimer:
The airbag Supplemental Restraint System (SRS) affords the driver and the front passenger
additional protection in moderate to severe frontal and side-impact collisions and outboard
2nd row passengers additional protection in moderate to severe side impact collisions. This
system provides supplemental protection only, and seat belts must be worn in order to avoid
injuries to out-of-position occupants upon bag deployment and to provide the best combined
protection in a serious accident. *Children should always be properly restrained in one of
the rear seats. See Owner's Manual for recommended seating position.

© Subaru of America, Inc. 2013

912 to 924

Supplemental Restraint System (SRS-604)

Table of Contents

SRS Airbag System Overview................................................................... 6
SRS System Precautions........................................................................... 6
Component Overview................................................................................ 7
Component Operation.............................................................................. 8
Roll Connector Phasing....................................................................... 10
Connector Double Lock Sensors......................................................11
Airbag Module............................................................................................ 12
Airbag............................................................................................................ 13
Airbag Deployment................................................................................... 13
Airbag Warning Lamps............................................................................. 14
Diagnostics and Servicing....................................................................... 14
SRS System Servicing............................................................................. 15
1996 Model Legacy and Outback.......................................................... 17
1998 Model Forester............................................................................... 18
2000 Model Legacy and Outback.......................................................... 20
2001 Model Legacy..................................................................................... 21
2002 Model Impreza WRX......................................................................... 22
2003 Supplemental Restraint System (SRS)..................................... 23
2005 Legacy Airbag System..................................................................... 26
Calibration Process................................................................................ 30
SRS Interior................................................................................................ 33
Side Impact Sensor................................................................................. 35
Subaru B9 Tribeca..................................................................................... 36
Pressure Sensor Type-Occupant Detection System................................ 36
2007 and Newer Tribeca Airbag Systems.......................................... 38
2008 Supplemental Restraint System (SRS)..................................... 39
2009 Forester SRS Airbags.................................................................... 42
2010MY Legacy and Outback................................................................... 43
2012MY Impreza Airbag Systems............................................................ 45
Occupant Detection System (ODS)..................................................... 51
2014 Forester............................................................................................. 56
Driver Side Front Airbag........................................................................... 56
Curtain Airbag.......................................................................................... 57
Knee Airbag............................................................................................. 58
Dual Deployment Seatbelt Pretensioners................................................ 59

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June 2013

Supplemental Restraint System (SRS-604)
SRS Test Harnesses................................................................................. 62
Special Tools............................................................................................. 62
Service Bulletins .................................................................................... 63
Tech TIPS....................................................................................................... 64

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June 2013

Supplemental Restraint System (SRS-604)
SRS Airbag System
Overview

SRS System Precautions

1. Whenever servicing the SRS System
disconnect the battery and wait at least
10 minutes before proceeding.

The SRS Airbag System is a safety device
designed to function in conjunction with a knee
bolster, seat belts, and shoulder belts. Similar
to other manufacturers, it deploys in frontal
and side collisions. It is an electrically operated
system which uses a chemical deployment
device.

2. Always store the SRS Airbag Module
(steering wheel pad) facing up.
3. All of the SRS components are sealed DO NOT DISASSEMBLE.
4. All of the SRS wiring is enclosed in a yellow
housing for quick identification. Use care
whenever working near a yellow housing.
These wires may not be repaired if they
are damaged. They MUST be replaced.
5. Do not drop any of the components. This
could alter their sensitivity.
6. The SRS Module must avoid extreme heat
exposure (200 degrees F. or greater).
NOTE:

5
SRS Components

The SRS System features built-in SelfDiagnostics and a redundant Safety Design
built into the SRS control module.

7. Wear protective clothing when handling
deployed Airbag components. Always
use gloves and eye protection. Although
the residue is NON toxic, it may cause
minor eye and skin irritation.

The system safeguards include double locking
connectors with Diagnostic Sensors, a selfshorting inflator SRS Airbag Module connector
to prevent accidental deployment during
servicing, and a Steering Roll Connector. A
capacitor supplies backup power.

8. Never place yourself or test equipment
between the Airbag Module and seat
when serving the Airbag System.
NOTE:

Finally, for redundancy, there are two front
Inertia Sensors and two Safety Sensor Circuits.
NOTE:

EXPOSURE TO TEMPERATURES
OF 300 DEGREES F. OR
GREATER WILL CAUSE
DEPLOYMENT.

THE SRS Airbag SYSTEM IS
THOROUGHLY DESIGNED
TO PREVENT ACCIDENTAL
DEPLOYMENT, HOWEVER,
CAUTION SHOULD ALWAYS
BE USED WHEN SERVICING
OR DIAGNOSING THE SYSTEM.
THE SRS SYSTEM, WHEN
HANDLED PROPERLY, IS LESS
HAZARDOUS TO SERVICE
THAN A CAR BATTERY OR
FUEL SYSTEM.
6

REVIEW ALL CAUTIONS
OUTLINED IN THE SERVICE
MANUAL REGARDING SKIN
AND EYE EXPOSURE TO
DEPLOYED Airbag RESIDUES.

June 2013

Supplemental Restraint System (SRS-604)
Component Overview

The following is an overview of the first
Subaru vehicle (1992 SVX) to be equipped
with the SRS Airbag system.
The Airbag and Inflator Module are attached to
the steering wheel and covered by the steering
wheel pad. It contains the Deployment module,
Airbag and cover pad.

9
Steering Roll Connector

The steering roll connector is mounted between
the steering wheel and the combination switch.
It is an integral part of the combination switch
assembly. The design of this assembly allows
for steering wheel rotation. It also provides
the hard wire connection between the Airbag
module and the SRS system harness.

7
Front Sensors and ECM

10
Double Lock Connector

8

All SRS connectors are equipped with double
locks and sensors. The sensors are used
to indicate that the connector is not doublelocked. For identification purposes, they are
green in color.

Front Sensor

There are two (2) front sensors located inside
the front fenders behind each inner fender
liner. In addition, there are two Safety Sensors
located inside the ECM.

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June 2013

Supplemental Restraint System (SRS-604)

Component Operation
The ECM controls the SRS Airbag System by
constantly monitoring the input signals from
the front sensors, the Safety Sensors and the
double lock circuit. It also generates output
signals to the warning lamps and to the inflator
module.

11
SRS ECM Location

The ECM is located under the center console.
It receives sensor input signals in the event
of a frontal impact. It then sends a signal to
trigger Airbag deployment. The ECM has selfdiagnostic capabilities, incorporating long term
memory.

14

The ECM sends a continuous low voltage
Open ECM
signal to monitor the sensors, the harness, the
deployment module, and to check for connector The ECM contains two Safety Sensors which
provide input signals, and two capacitors which
integrity.
supplement low battery voltage.
The capacitors also provide backup voltage in
the event of a total loss of battery voltage. They
are triggered by an internal voltage regulator.
NOTE:

12
Combination Meter

There are two (2) Airbag warning lamps
located in the combination meter. For safety
purposes, there are also two (2) independent
drive circuits. Only one lamp should illuminate
at time.

8

THE CAPACITORS CAN
ACTIVATE THE SRS Airbag UP
TO 10 MINUTES AFTER A TOTAL
LOSS OF BATTERY VOLTAGE.
THE REGULATOR MONITORS
BATTERY VOLTAGE AND
CAN SUPPLEMENT BATTERY
VOLTAGE AS NEEDED IN THE
EVENT OF A COLLISION.

June 2013

Supplemental Restraint System (SRS-604)

15

16

Front Sensor Cut-Away

Safety Sensor

Redundancy is provided by the front left hand
and right hand sensors. The hollow roller
design provides a movable mass. The roller
is mounted on a flat surface and held in place
by a flat roller spring. The roller spring allows
forward roller movement during frontal impacts
of 12.5 MPH or greater. In this case, the roller
and spring assembly makes contact with the
circuit terminal.

Two Safety Sensors located inside the ECM
provide redundancy. They operate similar
to the Front Sensors in that they provide a
B+ circuit to the Inflator. Although they are
similar in construction and operation to the
Front Sensors, the Safety Sensors are more
sensitive.

Weight added to the center of the roller makes it
heavier, which in turn, makes the sensor more
When the roller makes contact with the circuit sensitive to impact. The ECM must be replaced
terminal, it sends a collision signal to the ECM. if one of the Safety Sensors fail.
This completes the sensor circuit and provides
a ground circuit to the inflator.
The metal housing of the front sensors are
surrounded by resin and filled with inert gas
to prevent moisture damage.
CAUTION: DO NOT OPEN THE SENSOR
HOUSING. THE INTERNAL
COMPONENTS ARE NOT
SERVICEABLE.

The continuous sensor harness is molded
directly into the sensor body. The harness has
only one sensor connector, which is located
at the ECM. This provides a one-piece circuit
path to the ECM. A damaged harness or sensor
must be replaced as an assembly.

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Supplemental Restraint System (SRS-604)

Roll Connector Phasing
The roll connector MUST be phased to
the steering system. With the front wheels
centered, align the inner “center” indicator
(early versions of the SRS Airbag system)
located behind the window in the roll connector,
with the “center” indicator located on the
rotating cover next to the window. There is also
an alignment arrow on the connector case.

17
Steering Roll Connector

The Steering Roll Connector is a continuous flat
ribbon-type cable. The cable coils around the
hub which allows 2.65 turns (either direction)
from the center steering position. This provides
a direct hard wire connection between the SRS
Airbag Module and the ECM harness. It also
includes the Horn Circuit. This eliminates the
potential circuit interruption inherent to sliding
contact-type connectors, which also prevents
false trouble codes.

19
Roll Connector Indicator

Two guide pins are used to align the roll
connector with the steering wheel.

If the inner indicator shows “1R” in the window,
rotate the cover one full rotation to the right. If
the inner indicator shows “2R” in the window,
rotate the cover two full rotations to the right.
Similarly, if the indicator shows either “1L”
or “2L”, rotate the cover one or two left hand
rotations. Consult the service manual phasing
of newer model roll connectors.
NOTE:

10

TO MAINTAIN PROPER
STEERING WHEEL ALIGNMENT,
CENTER THE FRONT
WHEELS AND SCRIBE AN
ALIGNMENT MARK BETWEEN
THE STEERING WHEEL HUB
AND THE SHAFT, PRIOR TO
DISASSEMBLY.

June 2013

Supplemental Restraint System (SRS-604)
Connector Double Lock
Sensors

The following are examples from the 1992 SVX.
Double lock sensor mechanisms are identified
by a green color. They are used on all SRS
electrical connectors. The system uses four 4
double lock sensors between:
1. The main ECM connection

22

2. The system power supply and the warning
light.

Primary Double Lock Connector (unlocked)

Double lock sensor terminals make contact
when they are unlocked and they separate when
they are locked. The green tabs mechanically
4. The roll connector and the Airbag module prevent the connector from being removed. The
located behind the steering wheel pad.
primary double lock will not latch unless the
connectors are completely inserted.
3. The ECM harness and the roll connector
at the combination switch.

23

21
Schematic (Artwork)

Releasing Primary Double Lock

These sensors connect the double lock
detecting circuit to the negative side of the
igniter circuit. This provides a ground signal
circuit for the warning light system.

In order to release the primary double lock, use
a small screw driver. Press in on the metal loop
and simultaneously raise the green latch. Then
to remove the individual connectors, press
down on the primary connector locks.

If any green double-lock lever is not properly
latched, the SRS warning lamp will be
illuminated and a Trouble Code will be
displayed (Code 14).
The primary double lock at the ECM secures
the main harness connector as well as the two
front sensor harness connectors.

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June 2013

Supplemental Restraint System (SRS-604)
Note:

Double locks are utilized on all
models; however the double
lock sensing circuits have been
discontinued.

Airbag Module
The Airbag module comes as a one piece
assembly with the horn buttons. It is mounted
to the steering wheel with two or four #30
tamper-proof Torx bolts.

24
Connector Lock Operation

Secure the primary double lock by pressing the
green latch down until a click is heard.

27
Airbag Module (Artwork)

25

The Airbag module consists of three
subcomponents:

Two Step Lock

The procedure for locks #2 and #3 are similar
1. Inflator
to the primary double lock, except that they are
2. Airbag
released at the primary lock in two steps. First,
press down once on the spring-loaded green
3. Inflator harness with connector
latch and it will pop out. Then press it down a
second time in order to remove the connector. NOTE: The Airbag Module is serviced
To secure the double lock, push in the green
only as an assembly. DO NOT
latch until a click is heard.
attempt to disassemble or
repack the airbag.
Double lock locations:
1. The main ECM connection
2. The system power supply and the warning
light.
3. The ECM harness and the roll connector
at the combination switch.
4. The roll connector and the Airbag module
located behind the steering wheel pad.

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June 2013

Supplemental Restraint System (SRS-604)
Inflator Igniter

Airbag Deployment

The inflator igniter is designed to ignite a squib
after it receives an input from the ECM. The
igniter is an electrically heated device which
generates temperatures in excess of 300
degrees F. to ignite the squib.

In order to activate the system, a frontal force
of 12.5 MPH or greater is required. This force
overcomes the inertia and the tension of the
roller springs of the rollers in the front sensors
and the Safety Sensors. The rollers then make
contact with the circuit terminals. The front
sensors provide a ground circuit while the
Safety Sensors provide a positive circuit.
In order for the ECM to activate the inflator, it
must receive at least one collision signal from
the front sensors and at least one collision
signal from the Safety Sensors.

After receiving a signal from the ECM, the
igniter instantly heats up to 300 degrees F.,
igniting the squib which burns the nitrogen
pellets to create nitrogen gas. The generated
29
N2 goes through the screen into the Airbag.
The outer skin (steering wheel pad) of the
Squib (Artwork)
inflator Airbag module then ruptures as the
The squib consists of fire transmissive material Airbag deploys. The driver’s forward movement
used to ignite nitrogen pellets. The nitrogen is absorbed by the Airbag as it vents the N2
pellets generate nitrogen gas (N2) during through two 1.58 inch (40mm) holes.
combustion. This creates rapid gas expansion
The Operational Time Sequence is almost
which, in turn, inflates the Airbag.
instantaneous:
The built-in screen cools and removes hot
1. Collision: Zero seconds
cinders from the N2 before the N2 enters the
2. Operation of the inflator: 30 millisecond
Airbag.
3. Discharge of the N2: About 60 millisecond

Airbag

4. Completion: About 110 milliseconds

The Airbag itself is located behind the steering
NOTE:
wheel center pad. It is made out of nylon material
which expands to a diameter of approximately
30 inches (762mm) when inflated. (The design
and shape of the Airbags has changed over the
years to provide increased safety to the vehicle
occupants and to comply with government
regulations).

A VEHICLE WITH A DEPLOYED
Airbag MUST BE TOWED TO THE
DEALER FOR SERVICE.

The bag is coated on the inside with silicone
and is coated on the outside with talcum
powder or cornstarch. This provides lubrication