Mitsubishi Evolution X. Manual — part 675

SRS AIR BAG DIAGNOSIS

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SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-147

CAUTION

If DTC B1B21 is set in the SRS-ECU, always diag-
nose the CAN main bus line.

.

CIRCUIT OPERATION

• The SRS-ECU judges how severe a collision is

by detecting signals from the side impact sensors
installed on the lower side of the center pillar. If
the impact is over a predetermined level, the
SRS-ECU sends an ignition signal. At this time, if
the side collision safing G-sensor is on, the SRS
air bag will inflate.

• The ignition signal is input to the curtain air bag

module (RH) to inflate the curtain air bag.

.

DTC SET CONDITIONS

This DTC is set if there is abnormal resistance
between the input terminals of the curtain air bag
module (RH) (squib).

.

TROUBLESHOOTING HITS

• Damaged wiring harnesses or connectors

• Short to the power supply in the curtain air bag

module (RH) (squib) harness

• Malfunction of the SRS-ECU

DIAGNOSIS

Required Special Tools:

• MB991958: Scan Tool (M.U.T.-III Sub Assembly)

• MB991824: Vehicle Communication Interface (V.C.I.)

• MB991827: M.U.T.-III USB Cable

• MB991910: M.U.T.-III Main Harness A (Vehicles with

CAN Communication System)

• MB991865: Dummy resistor

• MB991866: Resister harness

AC708970AC

Connector: F-04

F-04 (B)

SRS AIR BAG DIAGNOSIS

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SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-148

STEP 1. Using scan tool MB991958, diagnose the CAN bus
line.

CAUTION

To prevent damage to scan tool MB991958, always turn the
ignition switch to the "LOCK" (OFF) position before con-
necting or disconnecting scan tool MB991958.
(1) Connect scan tool MB991958. Refer to "How to connect the

scan tool

P.52B-28

."

(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the CAN bus line found to be normal?

YES : Go to Step 2.
NO : Repair the CAN bus line (Refer to GROUP 54C,

Diagnosis

P.54C-14

).

STEP 2. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to "ON" position.
(3) Check if the DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?

YES : Go to Step 3.
NO : There is an intermittent malfunction such as poor

engaged connector(s) or open circuit (Refer to
GROUP 00, How to Use Troubleshooting/Inspection
Service Points

− How to Cope with Intermittent

Malfunctions

P.00-15

).

AC608435

Data link connector

MB991827

MB991824

MB991910

AB

SRS AIR BAG DIAGNOSIS

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SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-149

STEP 3. Check by dummy resistor connection.
(1) Disconnect the negative battery terminal.
(2) Disconnect the D-10 intermediate connector (connection

between curtain air bag harness and floor harness).

(3) Connect special tool MB991865 to special tool MB991866.

CAUTION

Do not insert a probe into the terminal from its front side
directly, as the connector contact pressure may be weak-
ened.
(4) Insert the probe of resistor harness, to which the dummy

resistor is installed, from the back of D-10 intermediate
connector (floor harness side).

(5) Connect the negative battery terminal.
(6) After erasing the diagnostic trouble code memory, check the

diagnostic trouble code again.

(7) Disconnect the negative battery terminal.
Q: Is DTC B1B21 set?

YES : Go to Step 4.
NO : Go to Step 5.

AC507310

D-10 Intermediate connector
(Curtain air bag harness side)

D-10
Intermediate
connector
(Floor harness side)

AI

MB991865
(Dummy resistor: 3 )

MB991866

(Resistor harness)

SRS AIR BAG DIAGNOSIS

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SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-150

STEP 4. Voltage measurement at the C-36 SRS-ECU
connector.
(1) Disconnect the negative battery terminal.
(2) While pushing the part "A" indicated in the figure of the

harness side connector, turn the lock lever to the direction
of the arrow to release the lock lever, and disconnect the
C-36 SRS-ECU connector.

DANGER

To prevent the air bag from deploying unintentionally,
disconnect the intermediate connector D-10 to short
the squib circuit.

(3) Disconnect the D-10 intermediate connector (connection

between curtain air bag harness and floor harness).

CAUTION

The short spring may not be released due to the insuffi-
cient insertion. Therefore, insert the insulator for 4 mm (0.6
inch) or more.
(4) Insert a cable tie [3 mm (0.12 inch) wide, 0.5 mm (0.02 inch)

thick] between terminal 39, 40 and the short spring to
release the short spring.

(5) Connect the negative battery terminal.
(6) Ignition switch: ON

(7) Measure the voltage between the C-36 wiring harness side

connector terminal No. 39, 40 and body ground.
Voltage should measure 0 volt

Q: Is the measured 0 volt?

YES : Go to Step 6.
NO : Repair the wiring harness.

AC609027

A

AB

Lock lever

AC507303 BZ

A

A

C-36 Harness side
connector (front view)

Section
A - A

Cable tie

Short spring

4 mm (0.16 inch) or more

Terminal

AC608813

C-36 Harness side
connector (front view)

BG