Mitsubishi Grandis. Manual — part 1023

TROUBLESHOOTING

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-144

DIAGNOSIS PROCEDURE

STEP 1. MUT-III CAN bus diagnostics

Use the MUT-III to diagnose the CAN bus lines.

Q: Is the check result normal?

YES :

Go to Step 2.

NO :

Repair the CAN bus line (Refer to GROUP
54D, Diagnosis

P.54D-16

).

STEP 2. Check whether the diagnosis code is
reset.

Check again if the diagnosis code is set.
(1) Erase the diagnosis code.

(2) Ignition: LOCK (OFF) position to ON
(3) On completion, check that the diagnosis code is

not reset.

Q: Is the diagnosis codes set?

YES :

Replace the SRS-ECU (Refer to

P.52B-223

).

NO :

There is an intermittent malfunction such as
poor engaged connector(s) or open circuit
(Refer to GROUP 00, How to Cope with
Intermittent Malfunction

P.00-5

).

B1548

CAN communication

• When the CAN communication are abnormal

B1549

• When the CAN communication are error

B1552

Changing of Power Supply

• Short circuit in the changing circuit

B1553

• Open circuit in the changing circuit

B1554

SG-BYPASS

• When the ASIC (frontal activation) are abnormal

B1555

• When the ROM or RAM are abnormal

B1557

ASIC

• When the ASIC are abnormal

Code No.

Part/Circuit integral to
SRS-ECU

Trouble causes

TROUBLESHOOTING

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-145

Code No.B1470: Seat Belt Pre-Tensioner (LH) (Squib) System Fault 1 (Short Circuit between
Terminals of the Squib Circuit)

CAUTION

If diagnosis code B1470 is set in the SRS-ECU,
always diagnose the CAN main bus line.

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 sends an
ignition signal. At this time, if the front air bag safing
G-sensor is on, the pre-tensioner will deploy.

DIAGNOSIS CODE SET CONDITIONS

This diagnosis code is set if there is abnormal
resistance between the input terminals of the seat
belt pre-tensioner (LH) (squib).

PROBABLE CAUSES

• Improper engaged connector or defective short

spring*

• Short circuit between the seat belt pre-tensioner

(LH) (squib) circuit terminals

• Damaged connector(s)

• Malfunction of the SRS-ECU

NOTE: *: The squib circuit connectors integrate a
"short" spring (which prevents the seat belt
pre-tensioner 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) (Refer to

P.52B-5

). Therefore, if

connector C-120 or D-19 is damaged or improperly
engaged, the short spring may not be released when
the connector is connected.

DIAGNOSIS PROCEDURE

STEP 1. MUT-III CAN bus diagnostics

Use the MUT-III to diagnose the CAN bus lines.

Q: Is the check result normal?

YES :

Go to Step 2 .

NO :

Repair the CAN bus line (Refer to GROUP
54D, Diagnosis

P.54D-16

).

STEP 2. Check whether the diagnosis code is
reset.

Check again if the diagnosis code is set.
(1) Erase the diagnosis code.
(2) Ignition: LOCK (OFF) position to ON

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

SEAT BELT
PRETENSIONER
(LH)

SRS-ECU

CONNECTOR
LOCK SWITCH

CONNECTOR
LOCK SWITCH

: CONNECTOR
CONNECTED: ON
CONNECTOR
DISCONNECTED: OFF

NOTE

Seat Belt Pre-Tensioner (LH) (Squib) Circuit

TROUBLESHOOTING

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-146

(3) On completion, check that the diagnosis code is

not reset.

Q: Is the diagnosis code 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 Cope with
Intermittent Malfunction

P.00-5

).

STEP 3. MUT-III diagnosis code

CAUTION

To prevent damage to MUT-III MB991958, always
turn the ignition switch to the "LOCK" (OFF)
position before connecting or disconnecting
MUT-III MB991958.
(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 B1519 set?

YES :

Go to Step 4.

NO :

Go to Step 5.

STEP 4. Connector lock check: SRS-ECU
connector C-120 (MUT-III diagnosis code)
(1) Disconnect the negative battery terminal.

(2) Disconnect the connectors C-120 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 B1470 set?

YES :

Go to Step 5.

NO :

The procedure is complete. It is assumed
that diagnosis code B1470 set as connector
C-120, D-19 was engaged improperly.

STEP 5. Connector lock check: SRS-ECU
connector C-120 and seat belt pre-tensioner (LH)
connector D-19 (MUT-III diagnosis code)
(1) Disconnect the negative battery terminal.

(2) Disconnect connectors C-120 and D-19, and then

reconnect them. For connector D-19, use a
flat-tipped screwdriver to unlock the locking
button at the harness side connector by
withdrawing it toward you in two stages, and then
disconnect the connector.

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

diagnosis code.

Q: Is diagnosis code B1470 set?

YES :

Go to Step 6.

NO :

The procedure is complete. It is assumed
that diagnosis code B1470 set because
connector C-120 or D-19 was engaged
improperly.

AC311438 AE

C-120 (Y)

Connector: C-120

Harness side
(front view)

AC311438 AE

C-120 (Y)

Connector: C-120

Harness side
(front view)

AC302393AC

D-19 (B)

Connector: D-19

Centre
pillar

Front vehicle

Harness side
(front view)

AC103556 AY

Locking button

Flat-tip screw
driver

D-19 Harness
side connector

D-19 Seat belt
pre-tensioner (LH)
connector

TROUBLESHOOTING

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-147

STEP 6. Check the driver's seat belt
pre-tensioner. (MUT-III diagnosis code.)
(1) Disconnect the negative battery terminal.

(2) Disconnect seat belt pre-tensioner (LH)

connector D-19. Use a flat-tipped screwdriver to
unlock the locking button at the harness side
connector by withdrawing it toward you in two
stages, and then disconnect the connector.

(3) Connect special tool dummy resistor (MB991865)

to special tool resistor harness (MB991884).

(4) Connect special tool MB991884 to the D-19

harness side connector.

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

the diagnosis code.

Q: Is diagnosis code B1470 set?

YES :

Go to Step 7.

NO :

Replace the seat belt pre-tensioner (LH).
(Refer to

P.52B-239

).

STEP 7. Check the seat belt pre-tensioner (LH)
circuit. Resistance measurement at the SRS-ECU
connector C-120.

(1) Disconnect SRS-ECU connector C-120.

DANGER

To prevent the seat belt pre-tensioner from
deploying unintentionally, disconnect the
seat belt pre-tensioner (LH) connector D-19
to short the squib circuit.

(2) Disconnect seat belt pre-tensioner (LH)

connector D-19. Use a flat-tipped screwdriver to
unlock the locking button at the harness side
connector by withdrawing it toward you in two

AC302393AC

D-19 (B)

Connector: D-19

Centre
pillar

Front vehicle

Harness side
(front view)

AC103556 AY

Locking button

Flat-tip screw
driver

D-19 Harness
side connector

D-19 Seat belt
pre-tensioner (LH)
connector

MB991884
MB991885

AC103283AV

MB991865
(Dummy resistor : 3

Ω)

MB991884
(Resistor
harness)

D-19 Harness side
connector

AC311438 AE

C-120 (Y)

Connector: C-120

Harness side
(front view)

AC302393AC

D-19 (B)

Connector: D-19

Centre
pillar

Front vehicle

Harness side
(front view)

AC103556 AY

Locking button

Flat-tip screw
driver

D-19 Harness
side connector

D-19 Seat belt
pre-tensioner (LH)
connector