Mitsubishi Montero (2004+). Manual - part 1008

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

TSB Revision

BASIC BRAKE SYSTEM

35A-31

STEP 8. Check the following harness wires.

• The wire between HBB connector B-17 (terminal 4) and 

M-ASTC-ECU connector E-119 (terminal 25)

• The wire between HBB connector B-17 (terminal 6) and 

M-ASTC-ECU connector E-119 (terminal 12)

• The wire between HBB connector B-17 (terminal 8) and 

M-ASTC-ECU connector E-119 (terminal 14)

Q: Is any harness wire damaged?

YES : Repair it and then go to Step 10.
NO :  Go to Step 9.

STEP 9. Recheck for diagnostic trouble code.
(1) Erase the DTC memory.
(2) Recheck for diagnostic trouble code.
Q: Is DTC 53 set?

YES : Replace the M-ASTC-ECU (Refer to GROUP 35C, 

M-ASTC-ECU 

P.35C-213

). Then go to Step 10.

NO :  It can be assumed that this malfunction is intermittent. 

Refer to GROUP 00, How to Use 
Troubleshooting/Inspection Service Points 

− How to 

Cope with Intermittent Malfunction 

P.00-6

.

AC204629 AE

CONNECTOR: B-17

B-17 (GR)

HARNESS CONNECTOR: 
COMPONENT SIDE

1

2

3

4

5

6

7

8

B-17

AC203901

AC204627AC

CONNECTOR: E-119

E-119

HARNESS CONNECTOR: 
COMPONENT SIDE

E-119

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

TSB Revision

BASIC BRAKE SYSTEM

35A-32

STEP 10. Recheck for diagnostic trouble code.
(1) Erase the DTC memory.
(2) Recheck for diagnostic trouble code.
Q: Is DTC 53 set?

YES : Start over at Step 1.
NO :  The procedure is complete.

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

TSB Revision

BASIC BRAKE SYSTEM

35A-33

DTC 54: Motor Relay (Open Circuit, Short Circuit or Failure of the Motor Relay Coil)

AC204495AB

Motor Relay Circuit

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

TSB Revision

BASIC BRAKE SYSTEM

35A-34

.

CIRCUIT OPERATION

• The motor relay A and the motor relay B are con-

trolled by the M-ASTC-ECU.

• If the brake fluid pressure in the hydraulic brake 

booster (HBB) becomes low, the M-ASTC-ECU 
outputs the motor relay actuating signal to the 
motor relay A and the motor relay B and then the 
pump motor operates.

• The M-ASTC-ECU monitors the pump motor (at 

25 terminal).

.

HBB DTC SET CONDITION
DTC 54 is set if the motor relay circuit is open or 
short, the motor relay A or the motor relay B is defec-
tive, or the internal circuit of the M-ASTC-ECU is 
defective.

.

TROUBLESHOOTING HINTS

• Malfunction of the motor relay A or the motor 

relay B

• Damaged wiring harness or connector

• Malfunction of the M-ASTC-ECU

.

DIAGNOSIS

Required Special Tool:

•  MB991958: Scan Tool (MUT-III Sub Assembly)

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

• MB991827: MUT-III USB Cable

• MB991911: MUT-III Main Harness B

• MB991223: Harness Set

AC204545 AC

CONNECTORS: B-17, B-18

B-17 (GR)

B-18 (B)

AC204329 AC

CONNECTORS: B-53X, B-54X

B-53X

B-54X

AC204688 AB

CONNECTOR: D-116

D-116

AC204547AB

CONNECTORS: D-208, D-212

D-208

D-212

JUNCTION BLOCK
(FRONT VIEW)

AC204548 AB

CONNECTOR: E-111

E-111

AC203901AD

CONNECTORS: E-119, E-120

E-119

E-120