Mitsubishi Montero (2002-2004). Manual — part 997
HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS
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BASIC BRAKE SYSTEM
35A-13
HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS
INTRODUCTION
M1351012800059
The hydraulic brake booster (HBB) accumulates the
high-pressure brake fluid in the accumulator by oper-
ating the pump motor. Even though the working
sound of the pump motor can be heard during opera-
tion, this sound is usually generated at normal opera-
tion of the HBB and is not an indication of a
malfunction.
HBB Diagnostic Trouble Code Detection
Conditions
HBB diagnostic trouble codes (HBB DTCs) are set
under different conditions, depending on the mal-
function detected. Most HBB DTCs will only be set
during vehicle operation. Some HBB DTCs will also
be set during the HBB self-check immediately after
the engine is started.
After erasing an HBB DTC, duplicate the HBB DTC
set conditions to see if it resets. Depending on the
detection timing and set conditions for the specific
HBB DTC, you must either drive the vehicle or turn
the engine off and restart it. To set the proper condi-
tions for that DTC again, refer to "HBB DTC SET
CONDITIONS" for each HBB DTC that you are trying
to reset.
DIAGNOSTIC TROUBLESHOOTING STRATEGY
M1351012900056
Use these steps to plan your diagnostic strategy. If
you follow them carefully, you will be sure that you
have exhausted most of the possible ways to find an
HBB fault.
1. Gather information about the problem from the
customer.
2. Verify that the condition described by the
customer exists.
3. Check the vehicle for any HBB DTC.
4. If you cannot verify the condition and no HBB
DTC sets, it can be assumed that the malfunction
is intermittent. Refer to GROUP 00, How to use
Troubleshooting/Inspection Service Points
− How
to Cope with Intermittent Malfunctions
5. If you can verify the condition but no HBB DTC
sets, or the system cannot communicate with the
scan tool, check that the basic brake system is
operating properly.
• If the basic brake system is not operating prop-
erly, refer to "Basic Brake System Diagnosis"
(
• If the basic brake system is operating properly,
refer to "Symptom Chart" (
6. If an HBB DTC sets, record the number of the
DTC, then erase the DTC from the memory using
the scan tool.
7. Duplicate the HBB DTC set conditions to see if
the same HBB DTC will set again.
• If the same HBB DTC sets again, perform the
diagnostic procedures for the DTC. Refer to
.
• If you cannot make the same HBB DTC set
again, it can be assumed that the malfunction is
intermittent. Refer to GROUP 00, How to use
Troubleshooting/Inspection Service Points
− How
to Cope with Intermittent Malfunctions
HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS
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BASIC BRAKE SYSTEM
35A-14
BRAKE WARNING LIGHT CHECK
M1351013000056
Check that the brake warning light illuminates as follows:
1. Check that the brake fluid level in the reservoir is between
the "MIN" and the "MAX" lines.
2. Choke the wheels and release the parking brake.
3. When the ignition switch is turned to the "ON" position, the
brake warning light illuminates.
4. When the ignition switch is turned from the "START" position
back to the "ON" position, the brake warning light illuminates
for approximately 3 seconds and then switches off.
5. If the illumination is other than the above, check the
diagnostic trouble codes.
TROUBLE CODE DIAGNOSIS
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Retrieving HBB Diagnostic Trouble Codes
Required Special Tool:
• MB991502: Scan Tool (MUT-II)
CAUTION
To prevent damage to scan tool MB991502, always turn the
ignition switch to the "LOCK" (OFF) position before con-
necting or disconnecting scan tool MB991502.
1. Connect scan tool MB991502 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Use scan tool MB991502 to check for HBB diagnostic
trouble codes.
4. Turn the ignition switch to the "LOCK" (OFF) position.
5. Disconnect scan tool MB991502.
Erasing HBB Diagnostic Trouble Codes
NOTE: If the M-ASTC-ECU functions have stopped due to the
fail-safe function, the HBB diagnostic trouble code cannot be
erased.
Required Special Tool:
• MB991502: Scan Tool (MUT-II)
AC000682 AB
BRAKE
WARNING
LIGHT
IGNITION
SWITCH
ILLUMINATED
NOT
ILLUMINATED
APPROXIMATELY 3S
LOCK, ACC
ON
START
BRAKE WARNING LIGHT
ACX01539
16-PIN
MB991502
AC
HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS
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BASIC BRAKE SYSTEM
35A-15
CAUTION
To prevent damage to scan tool MB991502, always turn the
ignition switch to the "LOCK" (OFF) position before con-
necting or disconnecting scan tool MB991502.
1. Connect scan tool MB991502 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Use scan tool MB991502 to erase HBB diagnostic trouble
codes.
4. Turn the ignition switch to the "LOCK" (OFF) position.
5. Disconnect scan tool MB991502.
DIAGNOSTIC TROUBLE CODE CHART
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Follow the inspection chart that is appropriate for the
diagnostic trouble code.
NOTE: If the trouble marked by * has occurred, the M-ASTC-ECU sounds the buzzer continuously to inform
the trouble of the driver and protects the pump motor by activating the pump motor intermittently.
ACX01539
16-PIN
MB991502
AC
DTC
INSPECTION ITEM
DIAGNOSTIC CONTENT
REFERENCE PAGE
16
Battery positive voltage
M-ASTC-ECU power supply voltage is
extremely low or high
31
Ignition switch circuit
Open circuit at the HBB power supply
sub circuit
53
Pump motor
• Seizure of the pump motor*
• Abnormality at the current detection
circuit of the M-ASTC-ECU
54
Motor relay
Open circuit, short circuit or failure of the
motor relay coil
55
Pump motor circuit
Pump motor energized abnormally for
long period*
56
Pressure switch
• Open circuit at the pressure switch (for
pump motor control)
• Open circuit or short circuit at the
pressure switch (for low-pressure
warning)
57
Accumulator
Accumulator low-pressure abnormality*
58
M-ASTC-ECU (Power supply
drive circuit)
Pump motor drive circuit in the M-ASTC-
ECU abnormality
Replace the M-ASTC-
ECU (Refer to
GROUP 35C, M-
ASTC-ECU
).
HYDRAULIC BRAKE BOOSTER (HBB) DIAGNOSIS
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BASIC BRAKE SYSTEM
35A-16
HBB DIAGNOSTIC TROUBLE CODE PROCEDURES
DTC 16: Battery Positive Voltage (M-ASTC-ECU Power Supply Voltage is Extremely Low or High)
CAUTION
If the battery voltage drops or rises while making this check, DTC 16 is set as an existing problem,
making it impossible to perform correct trouble diagnosis. Before carrying out the following diagno-
sis, test the battery and charge it if necessary.
AC204492AC
ASC-ECU Power Supply Circuit
AC204688 AB
CONNECTOR: D-116
D-116
AC204547AB
CONNECTORS: D-208, D-212
D-208
D-212
JUNCTION BLOCK
(FRONT VIEW)
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