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