Mitsubishi 380. Manual - part 427

AUTOMATIC TRANSMISSION DIAGNOSIS

AUTOMATIC TRANSMISSION

23A-248

INSPECTION PROCEDURE 13: Poor Acceleration

.

COMMENT

If acceleration is poor when downshifting occurs 
while driving, a malfunction of the engine system or a 
brake or clutch may exist.

.

TROUBLESHOOTING HINTS (The most 
likely causes for this condition:)

• Malfunction of the engine system

• Malfunction of the clutch system and brake sys-

tem

• Malfunction of the ENGINE-ECU or A/T-ECU sys-

tem

Circuit drawings

• Refer to circuit diagrams GROUP-

90

• Refer to configuration diagrams GROUP-

80

• Refer to component locations GROUP-

70

DIAGNOSIS

STEP 1. Check the engine system.
Refer to GROUP 13A, Diagnosis 

− Symptom Chart − Poor 

acceleration 

13A-21

.

Q: Is the inspection result good?

YES : Go to Step 2.
NO :  Repair or replace the engine component(s).

STEP 2. Check each brake and clutch.
Perform the torque converter stall test. Refer to 

P.23A-25

, 

Torque Converter Stall Test. Then retest the system.

Q: Is the symptom eliminated?

YES : The procedure is complete.
NO :  Go to Step 3.

STEP 3. Perform the hydraulic pressure test.
Perform the hydraulic pressure test. Refer to 

P.23A-26

, 

Hydraulic Pressure Test. Then retest the system.

Q: Is the symptom eliminated?

YES : The procedure is complete.
NO :  Go to Step 4.

STEP 4. Check each brake system and each clutch system.
(1) Remove the valve body cover and valve body. Refer to 

GROUP 23B, Transmission 

P.23B-13

.

(2) Blow 108 kPa (15 psi) compressed air into the each brake 

oil orifice and clutch oil orifice of the transmission case, and 
check if each brake and each clutch piston move and air 
pressure is maintained.

Q: Is the air pressure maintained?

YES : The procedure is complete.
NO :  Go to Step 5.

AUTOMATIC TRANSMISSION DIAGNOSIS

AUTOMATIC TRANSMISSION

23A-249

STEP 5. Check each brake system and clutch system.
(1) Remove the transmission.
(2) Check the facings for seizure and piston seal ring for 

damage and interference with retainer. Repair or replace 
the faulty parts. Refer to GROUP 23B, Transmission 

P.23B-13

, Underdrive Clutch and Input Shaft 

P.23B-46

, 

Reverse and Overdrive Clutch 

P.23B-48

. Then retest the 

system.

Q: Is the symptom eliminated?

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

AUTOMATIC TRANSMISSION DIAGNOSIS

AUTOMATIC TRANSMISSION

23A-250

INSPECTION PROCEDURE 14: Vibration

.

COMMENT

If vibration occurs when driving at constant speed or 
when accelerating in 5th gear (top range), abnormal 
damper control clutch pressure a malfunction of the 
engine system, damper control clutch solenoid, 
torque converter or valve body may exist.

.

TROUBLESHOOTING HINTS (The most 
likely causes for this condition:)

• Abnormal damper control clutch pressure

• Malfunction of the engine system

• Malfunction of the damper control clutch solenoid

• Malfunction of the torque converter

• Malfunction of the valve body

• Malfunction of the Engine or A/T system

Circuit drawings

• Refer to circuit diagrams GROUP-

90

• Refer to configuration diagrams GROUP-

80

• Refer to component locations GROUP-

70

DIAGNOSIS

Required Special Tool:

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

• MB991824: V.C.I.

• MB991827: MUT-III USB Cable

• MB991910: MUT-III Main Harness A

STEP 1. Using diagnostic tool MB991958, check actuator 
test item 6: Damper Control Clutch Solenoid Valve.

CAUTION

To prevent damage to diagnostic tool MB991958, always 
turn the ignition switch to the "LOCK" (OFF) position 
before connecting or disconnecting diagnostic tool 
MB991958. 
(1) Connect diagnostic tool MB991958 to the data link 

connector.

(2) Turn the ignition switch to the "ON" position.
(3) Set diagnostic tool MB991958 to the actuator test mode.

• Item 06: Damper Control Clutch Solenoid Valve.

• An audible clicking or buzzing should be heard when 

the damper control clutch solenoid valve is ener-
gized.

(4) Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the solenoid valve operating properly?

YES : Go to Step 2.
NO :  Repair or replace the damper control clutch solenoid 

valve. Refer to GROUP 23B, Valve Body 

P.23B-62

. 

Then confirm that the symptom is eliminated.

00DB076A

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

AUTOMATIC TRANSMISSION DIAGNOSIS

AUTOMATIC TRANSMISSION

23A-251

STEP 2. Check the vibration.

Q: Does the vibration occur when the transmission fluid 

temperature sensor connector has been disconnected?
YES : Check the engine system. Refer to GROUP 13A , 

Diagnosis 

− Symptom Chart − Driving 

13A-21

. If the 

inspection result is not good, diagnose, repair, and/or 
replace the engine component(s).

NO :  Go to Step 3.

STEP 3. Check the torque converter hydraulic pressure.
Measure the torque converter hydraulic pressure. Then check if 
the torque converter hydraulic pressure is within the standard 
value. Refer to 

P.23A-26

, Hydraulic Pressure Test.

Q: Is the torque converter hydraulic pressure within the 

standard value?
YES : Go to Step 4.
NO :  Go to Step 5.

STEP 4. Replace the torque converter assembly.
(1) Remove the transmission.
(2) Replace the torque converter assembly. Refer to GROUP 

23B, Transmission 

P.23B-13

. Then check the symptom.

Q: Is the symptom eliminated?

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

STEP 5. Disassemble and clean the valve body.
Check the O-ring installation bolts for looseness and the valve 
body for damage. Repair or replace the faulty parts. Refer to 
GROUP 23B, Valve Body 

P.23B-62

.

Replace the valve body assembly if the damages are thought 
to be irreparable. Then check the symptom.

Q: Is the symptom eliminated?

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

AC001857

VALVE BODY
ASSEMBLY

10DB117A