Mitsubishi Montero (2004+). Manual — part 1020

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

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BASIC BRAKE SYSTEM

35A-79

STEP 8. Recheck for diagnostic trouble code.
(1) Erase the DTC memory.
(2) Recheck for diagnostic trouble code.
Q: Is DTC 56 set?

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

DTC 57: Accumulator (Accumulator Low-Pressure Abnormality)

CIRCUIT OPERATION
The pressure switch (for low-pressure warning) mon-
itors brake fluid pressure inside of the hydraulic
brake booster (HBB). When the brake fluid pressure
decreases abnormally, the pressure switch (for
low-pressure warning) is turned off and the brake
fluid low-pressure warning signal is output to the
M-ASTC-ECU.

HBB DTC SET CONDITIONS
DTC 57 is set if the brake fluid pressure decreases,
or the pressure switch (for low-pressure warning)
OFF seize-up occurs. In this case, the M-ASTC-ECU
sounds the buzzer continuously to inform the trouble
of the driver and protects the pump motor by activat-
ing the pump motor intermittently.

AC204498AB

Pressure Switch (for Low-Pressure Warning) Circuit

AC204545AB

CONNECTOR: B-17

B-17 (GR)

AC203901AF

CONNECTOR: E-120

E-120

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

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BASIC BRAKE SYSTEM

35A-80

TROUBLESHOOTING HINTS

• Brake fluid leakage in the hydraulic brake booster

(HBB)

• Malfunction of the accumulator [Integrated with

the hydraulic brake booster (HBB)]

• Malfunction of the pressure switch (for low-pres-

sure warning) [Integrated with the hydraulic brake
booster (HBB)]

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 pressure switch (for low-pressure
warning) circuit inside the HBB.
(1) Depress the pedal repeatedly more than 40 times until the

pedal depressing force feels heavy with the ignition switch

at the "LOCK" (OFF) position to release the pressure of
HBB power supply system.

(2) Disconnect HBB connector B-17.

(3) Measure the resistance between the terminals 1 and 5 at

the HBB. The resistance should measure approximately 1
kilo ohms.

Q: Is the resistance approximately 1 kilo ohms?

YES : Go to Step 2.
NO : Replace the master cylinder and hydraulic unit

assembly (Refer to

P.35A-140

). Then go to Step 5.

AC204629 AC

CONNECTOR: B-17

B-17 (GR)

HBB CONNECTOR

B-17

AC204686 AB

HBB CONNECTOR

B-17

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

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BASIC BRAKE SYSTEM

35A-81

STEP 2. Check the leakage of brake fluid from the HBB
visually.
Q: Is there leakage of brake fluid from the HBB?

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

STEP 3. Disassemble and check the HBB.

(1) Remove the HBB (Refer to

P.35A-137

(2) Disassemble the HBB (Refer to

P.35A-140

(3) Check the HBB for the following points.

• Power piston assembly for rust, damage, wear and

deterioration

• Master cylinder piston assembly for rust, damage, wear

and deterioration

• Inside of the hydraulic unit assembly cylinder for rust

and damage

Q: Are all of the checked items in good condition?

YES : Assemble the HBB (Refer to

P.35A-140

), install the

HBB (Refer to

P.35A-137

), refill the brake fluid, and

bleed the brake line (Refer to

P.35A-125

). Then go to

Step 4.

NO : Replace the deficient parts, assemble the HBB (Refer

P.35A-140

), install the HBB (Refer to

P.35A-137

refill the brake fluid, and bleed the brake line (Refer to

P.35A-125

). Then go to Step 5.

STEP 4. Recheck for diagnostic trouble code.
(1) Erase the DTC memory.
(2) Recheck for diagnostic trouble code.
Q: Is DTC 57 set?

YES : Replace the accumulator (Refer to

P.35A-138

). Then

go to Step 5.

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 5. Recheck for diagnostic trouble code.
(1) Erase the DTC memory.
(2) Recheck for diagnostic trouble code.
Q: Is DTC 57 set?

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

HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS

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BASIC BRAKE SYSTEM

35A-82

SYMPTOM CHART

M1351013200050

NOTE: The hydraulic brake booster (HBB) accumulates the high-pressure oil in the accumulator by the acti-
vation of the pump motor to assist the brake power. Even though the working sound of the pump motor can
be heard during operation, this sound is usually generated at normal operation of the HBB and is not an indi-
cation of a malfunction.

SYMPTOM

INSPECTION
PROCEDURE NO.

REFERENCE
PAGE

Communication between the scan tool and the whole system is
not possible.

−

Refer to GROUP
13A, Diagnosis

P.13A-831

Communication between the scan tool and the M-ASTC-ECU is
not possible.

−

Refer to GROUP
35B, Diagnosis

P.35B-4

The brake warning light does not illuminate when the ignition
switch is turned to the "ON" position just after the engine start.