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1. OVERVIEW
The six speed automatic (M78) transmission is
available in two variants: four wheel drive and
two wheel drive.
The transmission has the following features:
Six Forward Speeds
One reverse gear
A torque converter with an integral converter lock-up clutch
Electronic shift and pressure controls
A single planetary gear-set
A double planetary gear-set
Two hydraulically controlled brake bands
Three multi-plate clutches
All hydraulic functions are directed by electronic solenoids to control: -
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Engagement feel
Shift feel
Shift scheduling
Modulated torque converter clutch applications ·
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The transmission contains fully synthetic automatic transmission fluid (ATF) and is filled for life; therefore
it does not require periodic servicing.
Engine power reaches the transmission via a torque converter with integral converter lock-up clutch.
The six forward gears and one reverse gear are obtained from a single planetary set, followed by a
double planetary set. This type of gear-set arrangement is commonly known as Lepelletier type gear-set.
The automatic transmission is electronically controlled. The control system is comprised of the following
elements:
External transmission control unit (TCU)
Internal embedded memory module (EMM)
Input and output speed sensors
Valve body unit comprised of four on/off solenoid valves and six variable bleed solenoids
Torque converter -
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2. FEATURES
Early Downshifts with Hard Braking and Skip Shifts ▶
When heavy braking is detected, the transmission downshifts early and skips gears to provide increased
engine braking to provide gear selection for tip-in.
Gear Hold on Uphill/Downhill ▶
If the accelerator pedal is released when travelling uphill, upshifts are prevented to reduce busyness on
grades. If the accelerator pedal is released when travelling downhill, upshifts are prevented to enhance
engine braking.
Soft Engagement when Shifting to “D” and “R” Position ▶
A soft engagement feature avoids harsh take up of drive when selecting Drive or Reverse. This is
achieved by limiting engine speed and engine torque which results in a rapid, but progressive
engagement of either Drive or Reverse when moving from the Park or Neutral positions. There is no
drive engagement prevention strategy implemented on the transmission system as there is sufficient
engine strategy to protect the system. However, reverse gear engagement is prevented until engine
speed is less than 1400 rpm and the accelerator pedal position is less than 12% and vehicle speed is
less than 10 km/h.
Converter Clutch Lock-Up In All Gears ▶
The transmission features converter clutch lock-up in all gears. This feature provides improved fuel
economy and vehicle performance. It also improves transmission cooling efficiency when towing heavy
loads at low speeds, e.g. in city driving or hill terrain.
Embeded Memory Module (EMM) ▶
The embedded memory module (EMM) is
matched to the transmission's valve bodies
during transmission assembly to ensure refined
shift quality. The EMM is integrated into the input
speed sensor which is mounted on the valve
body in the transmission. The EMM is used to
store data such as valve body calibration data
and valve body serial number. Upon installation,
the TCU will download the data from the EMM
and utilise this data in the operation of the
transmission.
1) Features
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2) Cooling System
The transmission cooling system ensures rapid warm-up and constant operating temperature resulting
in reduced fuel consumption and refined shift quality.
It also includes a cooler by-pass within the hydraulic system to allow sufficient cooling and lubrication to
the transmission drivetrain in the event of a blockage in the transmission cooler.
Gear Shift ▶
Coastdown ▶
Torque Demand ▶ Transmission gear change is controlled by the TCU. The TCU receives inputs from various engine and
vehicle sensors to select shift schedules and to control the shift feel and torque converter clutch (TCC)
operation at each gear change
Coastdown downshifts occur at 0% accelerator pedal when the vehicle is coasting down to a stop. To
reduce the shift shock and to improve the shift feeling during downshift, TCU electronically controls the
transmission.
Torque demand downshifts occur (automatically) when the driver demand for torque is greater than the
engine can provide at that gear ratio. If applied, the transmission will disengage the TCC to provide
added acceleration.
3) Shift Strategy
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3. MODE DESCRIPTIONS
1) Functions
Tip Switch in “M” Position (Manual Gear
Shift) (5)
The shiftable gear can be adjusted by
moving this switch to forward and rearward
when the gear select lever is in “M”
position. 5.Shift Lock Release Button Hole when Locked in the "P" Position (1)
If you cannot move the gear select lever from the "P" position, try to move the lever while
pushing down here with a sharp object such as a ballpoint pen. For your safety, turn off the
engine and depress the brake pedal before the attempt. 1.
Gear Position (4)
P :
R :
N :
D : 4.Mode Switch (3)
W :
S : 3.Selection of Manual/Automatic Shift Function (M↔D) (2)
D :
M : 2.
Automatic shift according to the driving condition
Manual shift
Winter mode (Start off the vehicle in 2nd gear)
Standard mode (Use the standard mode in normal driving conditions.)
Park
Reverse
Neutral
Drive
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2) Mode “M” (Manual Shift Mode)
This allows the driver to define the highest possible gear by selecting "+" or "-" on the gear selector when
the lever is in the "M" position. When the lever is first moved to the manual "M" position the transmission
will select the lowest possible gear.
When maximum engine rpm is reached the transmission will upshift automatically regardless of the
driver selected limit. 4WD models with low range will not automatically upshift when low range is
selected.
1st gear position ▶
2nd gear position ▶
3st gear position ▶
4th gear position ▶
5th gear position ▶
6th gear position ▶Use on a rugged road, mountain path and steep hill. Engine braking effect on steep hill is
available. -
Use on a long and gentle slope. 2-1 automatic kickdown shift is available. Engine braking effect is
available. -
Use on a long and gentle slope. 3-2 and 2-1 automatic kickdown shift is available. Engine
braking effect is available. -
Use on a long and gentle slope. 4-3, 4-2 and 4-1 automatic kickdown shift is available. -
5-4 and 5-3 automatic kickdown shift is available. -
6-5 and 6-4 automatic kickdown shift is available. -
Kickdown Function
If you need to accelerate rapidly, depress the accelerator pedal completely to the floor.
Then, a one- or two-lever gear will automatically be engaged. This is called the Kickdown function.
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4. LIMP HOME MODE
In case of transmission malfunction ▶
If a serious fault occurs in the automatic transmission, the TCU enters the limp home mode to
secure safe driving and protect the automatic transmission.
As power is no longer supplied to the solenoid, the current basic function (P, R, N, D) is
maintained and the 4th gear can be maintained only by the operation of the hydraulic system
without electrical operation.
The ECU communicates with other electric modules with CAN. If a serious fault occurs, the
transmission automatically enters the limp home mode for service.
The TCU monitors all factors which can affect to the performance of the transmission and
diagnose the system according to OBD II regulation. 1.
2.
3.
4.
In case of overheated transmission ▶
The TCU enters the limp home mode when the batter voltage drops below 8 V.
If the transmission is overheated, the shift pattern is changed to the hot mode to cool the
transmission more efficiently.
While the transmission is overheated, the selector lever symbol and engine temperature warning
lamp on the instrument cluster blink until the transmission is cooled down to the normal operation
temperature. If the transmission is excessively overheated, the gear cannot be shifted but
remains in the neutral position. 1.
2.
3.
Towing the vehicle with A/T ▶
The best way to transport the vehicle is to load it to a truck and transport it, especially if the vehicle is
4WD.
If towing the vehicle with the propeller shaft connected, the transmission or oil pump of transfer case
may malfunction, resulting in internal damage due to poor lubrication. -
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5. ELECTRONIC CONTROL SYSTEM
1) Overview
The transmission control unit (TCU) and its input/output networks control the operations of transmission:
Shift timing
Line pressure
Clutch pressure (shift feel)
Torque converter clutch -
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In addition, the TCU receives input signals from certain transmission-related sensors and switches. The
TCU also uses these signals when determining transmission operating strategy. Using all of these input
signals, the TCU can determine when the time and conditions are right for a shift, or when to apply or
release the torque converter clutch. It will also determine the pressure needed to optimise shift feel. To
accomplish this, the TCU operates six variable bleed control solenoids and four ON/OFF solenoids to
control the operations of transmission.
2) Transmission Control Unit (TCU)
The transmission control unit (TCU) is mounted under the driver's seat and controls the operation of the
transmission.
TCU processes the analog information from the internal sensors and the digital information through CAN
communication lines. TCU monitors all the input and output signals. If there is any failure, TCU changes
the system to “Limp Home Mode” and alerts to the driver through the warning lamp on the
instrument cluster.
(1) Hard-wired (Analog) Input/Output
Input/Output Data between TGS Lever and TCU ▶
Position and conditions of gear select lever
Driving moded (Winter or Standard) -
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Position of inhibitor switch - Input/Output Data between Inhibitor and TCU ▶
6 control signals for variable bleed solenoid
4 control signals for ON/OFF solenoid
Transmission input speed
Transmission output speed
Transmission oil temperature
EMM (Embeded Memory Module) -
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- Input/Output Data between Automatic Transmission and TCU ▶
Input/Output Data between Self Diagnostic Connector and TCU ▶
Various DTC codes and TCU information -
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(2) CAN Input/Output
TCU receives and sends the data among the units through P-CAN communication.
CAN Input/Output Data between Engine ECU and TCU ▶