Mitsubishi Lancer Evolution IX. Manual - part 626

TROUBLESHOOTING

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-17

Code No.21: Driver's air bag module (squib) system (short-circuited between terminals of the squib
circuit)

OPERATION

• The SRS-ECU judges how severe a collision is

by detecting signals from the front impact sensors
and the front air bag analogue G-sensor. If the
impact is over a predetermined level, the
SRS-ECU outputs an ignition signal. At this time,
if the front air bag safing G-sensor is on, the SRS
air bag will inflate.

• The ignition signal is input to the air bag module

via the clock spring to inflate the air bag.

DIAGNOSIS CODE SET CONDITIONS

This diagnosis code is set if one driver's air bag
squib wire shorted to the other. However, if no diag-
nosis code resets, the SRS warning lamp will be
switched off (diagnosis code will be retained).

PROBABLE CAUSES

• Improper engaged connector or defective short

spring*

• Short circuit in the clock spring

• Short circuit between the driver's air bag module

(squib) circuit terminals

• Damaged connector(s)

• Malfunction of the SRS-ECU

NOTE: *: The squib circuit connectors integrate a
"short" spring (which prevents the air bag from
deploying unintentionally due to static electricity by
shorting the positive wire to the earth wire in the
squib circuit when the connectors are disconnected).
Therefore, if connector C-12, C-205 or C-201 is dam-
aged or improperly engaged, the short spring may
not be released when the connector is connected.

CONNECTOR
LOCK
SWITCH

CLOCK
SPRING

AIR BAG MODULE
(SQUIB)
(DRIVER'S SIDE)

AIR BAG
DRIVE CIRCUIT

SRS-ECU

MICROCOMPUTER

Wire colour code
B : Black LG : Light green G : Green L : Blue W : White Y : Yellow SB : Sky blue
BR : Brown O : Orange GR : Gray R : Red P : Pink V : Violet

NOTE

: CONNECTOR
COUPLED: ON
CONNECTOR
UNCOUPLED: OFF

Driver's Air Bag Module (Squib) Circuit

: LH drive vehicles
: RH drive vehicles

TROUBLESHOOTING

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-18

DIAGNOSIS PROCEDURE

STEP 1.M.U.T.-II/III diagnosis code

CAUTION

To prevent damage to M.U.T.-II/III, always turn the
ignition switch to the "LOCK" (OFF) position
before connecting or disconnecting M.U.T.-II/III.
(1) Turn the ignition switch to the "ON" position.
(2) Check if the diagnosis code is set.
(3) Turn the ignition switch to the "LOOK" (OFF)

position.

Q: Is diagnosis code 34 set?

YES :

Go to Step 2.

NO :

Go to Step 3.

STEP 2. Connector lock check: SRS-ECU
connector C-12 (M.U.T.-II/III diagnosis code)
(1) Disconnect the negative battery terminal.

(2) Disconnect connectors C-12 and then reconnect

them.

(3) Connect the negative battery terminal.
(4) Erase the diagnosis code memory, and check the

diagnosis code.

Q: Is diagnosis code 21 set?

YES :

Go to Step 4.

NO :

The procedure is complete. It is assumed
that diagnosis code 21 set as connector
C-12 was engaged improperly.

STEP 3. Connector lock check: SRS-ECU
connector C-12 clock spring connector C-205
and driver’s air bag module connector C-201.
(M.U.T.-II/III diagnosis code)
(1) Disconnect the negative battery terminal.

(2) Disconnect connectors C-12, C-205 and C-201,

and then reconnect them.

(3) Connect the negative battery terminal.
(4) Erase the diagnosis code memory, and check the

diagnosis code.

Q: Is diagnosis code 21 set?

YES :

Go to Step 4.

NO :

The procedure is complete. It is assumed
that diagnosis code 21 set as connector
C-12, C-205 or C-201 was engaged
improperly.

AC101950AJ

SRS-ECU

Harness side
connector
(rear view)

C-12 (Y)

Connector: C-12

AC101950AJ

SRS-ECU

Harness side
connector
(rear view)

C-12 (Y)

Connector: C-12

AC310479

Connectors: C-201, C-205
<LHD>

C-205 (Y)

C-201

C-205 Harness side
connector (rear view)

C-201 Harness side
connector (rear view)

AC310481AF

Connectors: C-201, C-205
<RHD>

C-205 (Y)

C-205 Harness side
connector (rear view)

C-201 Harness side
connector (rear view)

C-201

TROUBLESHOOTING

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-19

STEP 4. Check the diagnosis code by connecting
a dummy resistor. (M.U.T.-II/III diagnosis code)
(1) Disconnect the negative battery terminal.

(2) By sliding the A section (in the figure) of air bag

module connector C-201 in the arrow direction,
disconnect the connector.

(3) Connect special tool dummy resistor (MB991865)

to special tool resistor harness (MB991866).

CAUTION

Do not insert a test probe into the terminal from
its front side directly as the connector contact
pressure may be weakened.
(4) Insert special tool (MB991866) into clock spring

side air bag module connector C-201 by
backprobing.

(5) Connect the negative battery terminal.
(6) Erase the diagnosis code memory, and check the

diagnosis code.

Q: Is diagnosis code 21 set?

YES :

Go to Step 5.

NO :

Replace the driver's air bag module (Refer
to

P.52B-110

STEP 5. Check the diagnosis code by connecting
a dummy resistor. (M.U.T.-II/III diagnosis code)
(1) Disconnect the negative battery terminal.

(2) Disconnect the clock spring connector C-205.

(3) Connect special tool dummy resistor (MB991865)

to special tool resistor harness (MB991866).

CAUTION

Do not insert a test probe into the terminal from
its front side directly as the connector contact
pressure may be weakened.
(4) Insert special tool (MB991866) into clock spring

harness side connector C-205 (terminal No.3 and
4) by backprobing.

(5) Connect the negative battery terminal.
(6) Erase the diagnosis code memory, and check the

diagnosis code.

AC105823

AC304700

AC305145AE

Steering
wheel

C-201 Air bag
module connector

AC300945AE

MB991865
(Dummy resistor : 3 )

MB991866
(Resistor harness)

C-201 Air bag
module
connector

AC310479

Connector: C-205 <LHD>

C-205 (Y)

Harness side
connector
(rear view)

AC310481AG

Connector: C-205 <RHD>

C-205 (Y)

Harness side
connector
(rear view)

AC300949AC

MB991865 (Dummy
resistor : 3 )

MB991866
(Resistor harness)

C-205 Clock spring
connector

(Rear view)

TROUBLESHOOTING

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-20

Q: Is diagnosis code 21 set?

YES :

Go to Step 6.

NO :

Replace the clock spring (Refer to

P.52B-110

STEP 6. Resistance measurement at the
SRS-ECU connector C-12.

(1) Disconnect SRS-ECU connector C-12.

DANGER

To prevents the air bag from deploying unin-
tentionally, disconnect the clock spring con-
nector C-205 to short the squib circuit.

(2) Disconnect the clock spring connector C-205.

CAUTION

Insert an insulator such as a cable tie to a depth
of 4 mm or more, otherwise the short spring will
not be released.
(3) Insert a cable tie [3 mm wide, 0.5 mm thick]

between terminals 11, 12 and the short spring to
release the short spring.

CAUTION

Do not insert a test probe into the terminal from
its front side directly as the connector contact
pressure may be weakened.
(4) Resistance measurement between C-12 harness

side connector terminals 11 and 12.

OK: Open circuit

Q: Is the check result normal?

YES :

Go to Step 7.

NO :

Repair the harness wires between
SRS-ECU connector C-12 (terminal No.11
and 12 and clock spring connector C-205
(terminal No.3 and 4).

STEP 7. Check whether the diagnosis code is
reset.

Q: Is diagnosis code 21 set?

YES :

Replace the SRS-ECU (Refer to

P.52B-109

NO :

An intermittent malfunction is suspected
(Refer to GROUP 00

− How to Use

Troubleshooting/Inspection Service Points

P.00-5

AC101950AJ

SRS-ECU

Harness side
connector
(rear view)

C-12 (Y)

Connector: C-12

AC310479

Connector: C-205 <LHD>

C-205 (Y)

Harness side
connector
(rear view)

AC310481AG

Connector: C-205 <RHD>

C-205 (Y)

Harness side
connector
(rear view)

AC100391BG

Section
A - A

Cable tie

Short spring

4 mm or more

Terminal

C-12 Harness side
(front view)

C-12 Harness side
(rear view)

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