Mitsubishi Montero (2004+). Manual - part 1005

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

TSB Revision

BASIC BRAKE SYSTEM

35A-19

.

CIRCUIT OPERATION
The M-ASTC-ECU has two power supply lines. An 
M-ASTC-ECU power is supplied to the 
M-ASTC-ECU (terminal 9) from the ignition switch 
(IG2) through the multi-purpose fuse number 17 in 
the junction block. The other M-ASTC-ECU power is 
supplied to the M-ASTC-ECU (terminal 63) from the 
ignition switch (IG2) through the multi-purpose fuse 
number 5 in the junction block and through the joint 
connector number 4. 

.

HBB DTC SET CONDITIONS
DTC16 is set if the voltage at both of the power line is 
extremely low or high.

.

TROUBLESHOOTING HINTS

• Malfunction of the battery

• Malfunction of the charging system

• Malfunction of the M-ASTC-ECU

.

DIAGNOSIS

Required Special Tools:

•  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

STEP 1. Check the battery.

Refer to GROUP 54A, Battery 

− On-vehicle Service 

− Battery Testing Procedure 

P.54A-6

.

Q: Is the battery damaged?

YES : 

Charge or replace the battery and then go 

to Step 4.

NO : 

Go to Step 2.

STEP 2. Check the charging system.
Refer to GROUP 16, Charging System 

− Diagnosis 

P.16-3

.

Q: Is the charging system damaged?

YES : 

Repair the Charging System and then go to 

Step 4.

NO : 

Go to Step 3.

STEP 3. Recheck for diagnostic trouble code.
(1) Erase the DTC memory.
(2) Recheck for diagnostic trouble code.

Q: Is DTC 16 set?

YES : 

Replace the M-ASTC-ECU (Refer to 

GROUP 35C, M-ASTC-ECU 

P.35C-213

). 

Then go to Step 4.

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

.

STEP 4. Recheck for diagnostic trouble code.
(1) Erase the DTC memory.
(2) Recheck for diagnostic trouble code.

Q: Is DTC 16 set?

YES : 

Start over at Step 1.

NO : 

The procedure is complete.

AC204548 AB

CONNECTOR: E-111

E-111

AC203901AD

CONNECTORS: E-119, E-120

E-119

E-120

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

TSB Revision

BASIC BRAKE SYSTEM

35A-20

DTC 31: Ignition Switch B Circuit (Open Circuit at the HBB Power Supply Sub Circuit)

.

CIRCUIT OPERATION
In the ignition switch B circuit, the M-ASTC-ECU 
power is supplied to the M-ASTC-ECU (terminal 9) 
from the ignition switch (IG2) through the multi-pur-
pose fuse number 17 in the junction block. 

.

HBB DTC SET CONDITIONS
DTC31 is set if the ignition switch B circuit is open or 
the internal circuit of the M-ASTC-ECU is defective.

.

TROUBLESHOOTING HINTS

• Damaged wiring harness or connector

• Malfunction of the M-ASTC-ECU

.

AC204493 AB

HBB Power Supply Sub Circuit

AC204548 AB

CONNECTOR: E-111

E-111

AC203901AE

CONNECTOR: E-119

E-119

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

TSB Revision

BASIC BRAKE SYSTEM

35A-21

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

STEP 1. Check the following connector.

• M-ASTC-ECU connector E-119

Check connector, for loose, corroded or damaged terminals, or 
terminals pushed back in the connector.
Q: Are the connector and terminals in good condition?

YES : Go to Step 2.
NO :  Repair it and then go to Step 5.

AC203901

AC204627 AB

CONNECTOR: E-119

E-119

M-ASTC-ECU CONNECTOR

E-119

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

TSB Revision

BASIC BRAKE SYSTEM

35A-22

STEP 2. Check the power supply circuit at M-ASTC-ECU 
harness connector E-119.

(1) Disconnect M-ASTC-ECU connector E-119 and measure at 

the harness connector (component side).

(2) Start the engine.

(3) Measure the voltage between terminal 9 and ground. It 

should measure approximately 12 volts (battery positive 
voltage).

Q: Is battery positive voltage (approximately 12 volts) 

present?
YES : Go to Step 4.
NO :  Go to Step 3.

AC203901

AC204627 AB

CONNECTOR: E-119

E-119

M-ASTC-ECU CONNECTOR

E-119

AC204549AC

HARNESS CONNECTOR: 
COMPONENT SIDE

E-119