Mitsubishi Galant 9G. Manual - part 257

MANUAL A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-104

STEP 2. Using scan tool MB991958, read the powertrain
control module diagnostic trouble code.
Check that the middle-grade multi-center display unit sets a
DTC.
(1) Turn the ignition switch to the "ON" position.
(2) Check for the DTC related to the middle-grade multi-center

display unit.

(3) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the check result satisfactory?

YES : Go to Step 3.
NO : Refer to GROUP 54A, Middle-grade multi-center

display unit

− Diagnosis

P.54A-224

STEP 3. Using scan tool MB991958, check for any
diagnostic trouble code.
Check if a DTC, which relates to CAN communication-linked
systems below, is set.

• ETACS-ECU

DTC indicating a time-out error of middle-grade multi-center
display unit

(1) Turn the ignition switch to the "ON" position.
(2) Check for a DTC related to the relevant system.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the check result satisfactory?

YES : Go to Step 5.
NO : Go to Step 4.

AC305412

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

AC305412

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

MANUAL A/C DIAGNOSIS

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HEATER, AIR CONDITIONING AND VENTILATION

55A-105

STEP 4. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Turn the ignition switch to the "ON" position.
(2) Check if the DTC is set.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the check result satisfactory?

YES : A poor connection, open circuit or other intermittent

malfunction is present in the CAN bus lines between
the middle-grade multi-center display unit and the
A/C-ECU (Refer to GROUP 00, How to Use
Troubleshooting/Inspection Service Points

− How to

Cope with Intermittent Malfunctions

P.00-14

NO : Replace the middle-grade multi-center display unit.

On completion, check that the DTC is not reset.

STEP 5. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Turn the ignition switch to the "ON" position.
(2) Check if the DTC is set.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the check result satisfactory?

YES : A poor connection, open circuit or other intermittent

malfunction is present in the CAN bus lines between
the middle-grade multi-center display unit and the
A/C-ECU (Refer to GROUP 00, How to Use
Troubleshooting/Inspection Service Points

− How to

Cope with Intermittent Malfunctions

P.00-14

NO : Replace the A/C-ECU. On completion, check that the

DTC is not reset.

AC305412

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

AC305412

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

MANUAL A/C DIAGNOSIS

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HEATER, AIR CONDITIONING AND VENTILATION

55A-106

DTC U1120: Failure Information on Powertrain Control Module (Related to Engine)

CAUTION

If DTC U1120 is set in the A/C-ECU, diagnose the
CAN main bus line.

CAUTION

Whenever the ECU is replaced, ensure that the
communication circuit is normal.

CAUTION

The engine control system- related DTC may be
set when DTC U1120 is set. (For details refer to
GROUP 00, Intersystem Affiliated DTC Reference
Table

P.00-17

.) Diagnose the engine control sys-

tem first when the engine control system- related
DTC is set.

TROUBLE JUDGMENT

The A/C-ECU receives engine control sys-
tem-related signal from the powertrain control mod-
ule by the CAN bus lines. If a fail-safe related data is
contained in the signal from the powertrain control
module, DTC U1120 will be stored.

TECHNICAL DESCRIPTION (COMMENT)

Current trouble

• The wiring harness wire or connectors may have

loose, corroded, or damage terminals, or termi-
nals pushed back in the connector, the power-
train control module, or the A/C-ECU may be
defective.

Past trouble

• If DTC U1120 is stored as a past trouble, carry

out diagnosis with particular emphasis on wiring
and connector(s) in the CAN bus line between
the A/C-ECU and the powertrain control module,
and the power supply system to the powertrain
control module. If the connectors and wiring are
normal, and obviously the ECU is the cause of
the trouble, replace the ECU. If in doubt, do not
replace the ECU.
NOTE: For a past trouble, you cannot find it by
the scan tool CAN bus diagnostics even if there is
a failure in CAN bus lines. In this case, refer to
GROUP 00, How to Use Troubleshooting/Inspec-
tion Service Points

−

How to Cope with Intermit-

tent Malfunctions

P.00-14

.) and check the CAN

bus lines. You can narrow down the possible
cause of the trouble by referring to the DTC,
which is set regarding the CAN communica-
tion-linked ECUs (Refer to GROUP 54C

−

Expla-

nation about the scan tool CAN bus diagnostics

P.54C-6

TROUBLESHOOTING HINTS

• Malfunction of the A/C-ECU.

• Malfunction of the powertrain control module.

DIAGNOSIS

Required Special Tool:

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

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

• MB991827: MUT-III USB Cable

• MB991910: MUT-III Main Harness A (Vehicles with CAN

communication system)

MANUAL A/C DIAGNOSIS

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STEP 1. Using scan tool MB991958, diagnose the CAN bus
line.

CAUTION

To prevent damage to scan tool (MUT-III), always turn the
ignition switch to the "LOCK" (OFF) position before con-
necting or disconnecting scan tool (MUT-III).
(1) Connect scan tool MB991958 to the data link connector.
(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the CAN bus line found to be normal?

YES : Go to Step 2.
NO : Repair the CAN bus line (Refer to GROUP 54C,

Diagnosis

P.54C-14

STEP 2. Using scan tool MB991958, read the powertrain
control module diagnostic trouble code.
Check whether any engine or automatic transmission DTCs are
set or not.
(1) Turn the ignition switch to the "ON" position.
(2) Check for engine and automatic transmission DTCs.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the check result satisfactory?

YES : Refer to GROUP 13A, Diagnostic Trouble Code

P.13A-33

<2.4L> or GROUP 13B, Diagnostic Trouble

Code

P.13B-34

<3.8L>.

NO : Go to Step 3.

AC305412

MB991910

DATA LINK

CONNECTOR

MB991824