1998 SSANGYONG MUSSO Workshop Repair Manual

5A-24 AUTOMATIC TRANSMISSION
Transmission Control Unit(TCU)
The TCU is an in-vehicle micro-processor based transmission management system. It is usually mounted in the
vehicle cabin, under the instrument panel, under the seat, behind the side kick panels or under the floor in the
footwell on the passenger side. Different control units are supplied for different vehicle applications.
The TCU contains:
lProcessing logic circuits which include a central microcontroller and a back-up memory system.
lInput circuits.
lOutput circuits which control external devices such as the variable pressure solenoid (VPS), on/off solenoid
drivers, a diagnostics output and the driving mode indicator light.
The various items which make up the TCU are discussed below.
Processing Logic
Shift schedule and calibration information is stored in an erasable programmable read only memory (EEPROM).
Throttle input calibration constants and the diagnostics information are stored in electrically erasable programmable
read only memory (EEPROM) that retains the memory even when power to the TCU is disconnected.
In operation the software continuously monitors the input values and uses these, via the shift schedule, to determine
the required gear state, At the same time it monitors, via the solenoid outputs, the current gear state. Whenever the
input conditions change such that the required gear state is different to the current gear state, the TCU initiates a
gear shift to bring the two states back into line.
Once the TCU has determined the type of gear shift required the software accesses the shift logic, estimates the
engine torque output, adjusts the variable pressure solenoid ramp pressure then executes the shift.
The TCU continuously monitors every input and output circuit for short or open circuits and operating range. When
a failure or abnormal operation is detected the TCU records the condition code in the diagnostics memory and
implements a limp mode, The actual limp mode used depends upon the failure detected with the object to maintain
maximum driveability without damaging the transmission. In general input failures are handled by providing a default
value. Output failures, which are capable of damaging the transmission, result in full limp mode giving only third or
fourth gear and reverse. For further details of limp modes and memory retention refer to the Diagnostic Section.
The TCU is designed to operate at ambient temperatures between -40 and 85°C . It is also protected against
electrical noise and voltage spikes, however all the usual precautions should be observed, for example when arc
welding or jump starting.
TCU Inputs
To function correctly, the TCU requires engine speed, road speed, transmission sump temperature, throttle position
and gear position inputs to determine the variable pressure solenoid current ramp and on/off solenoid states. This
ensures the correct gear selection and shift feel for all driving conditions.
The inputs required by the TCU are as follows:
lEngine Speed
The engine speed signal is derived from the tachometer signal line, a dedicated sensor or a Controlled Area
Network (CAN).
lRoad Speed
4WD (Diesel) - The shaft speed signal is derived from the speedo sensor located on the transfer case. This signal
is transmitted directly to the TCU.
4WD (Gasoline) - The speedo sensor sends the shaft speed signal to the engine control module (ECM). The
information is then transferred to the TCU via the CAN.
lTransmission Sump Temperature
The transmission sump temperature sensor is a thermistor located in the solenoid wiring loom within the transmission.
This sensor is a typical NTC resistor with low temperatures producing a high resistance and high temperatures

AUTOMATIC TRANSMISSION 5A-25
producing a low resistance.
Temperature/Resistance characteristics and location within the solenoid wiring loom are given in tables 3-1 and 3-
2, and figures 3.2 and 3.3.
If the transmission sump temperature exceeds 135°C, the TCU will impose converter lock-up at lower vehicle
speeds and in some vehicles flashes the mode indicator lamp. This results in maximum oil flow through the
external oil cooler and eliminates slippage in the torque converter. Both these actions combine to reduce the oil
temperature in the transmission.
Connects To
Solenoid 1
Solenoid 2
Solenoid 3
Solenoid 4
Solenoid 5
Solenoid 6
Solenoid 7
Solenoid 5
Temp Sensor
Temp SensorWire Color
Red
Blue
Yellow
Orange
Green
Violet
Brown
Green
White
WhitePin No.
1
2
3
4
5
6
7
8
9
10
Table 3.2 - Pin No. Codes for Temperature Sensor Location In Solenoid Loom
Figure 3.3 - Temperature Sensor Location in Solenoid Loom

5A-26 AUTOMATIC TRANSMISSION
Inhibitor
Switch Throttle Position Sensor
The throttle position sensor(TPS) is a resistance potentiometer
mounted on the throttle body of the engine.
It transmits a signal to the TCU proportional to the throttle plate
opening.
The potentiometer is connected to the TCU by three wires:
5 volts positive supply, earth and variable wiper voltage.
Throttle voltage adjustments are as follows:
lClosed throttle voltage is 0.2V to 1.0V.
lWide open throttle voltage is 3V -4.7V.
These measurements are taken between pins 29 and 27 of
the TCU.
Maintaining good shift feel through the transmission life span
is dependant on having an accurate measure of
the engine throttle position. To achieve this the TCU
continuously monitors the maximum and minimum throttle
potentiometer voltages and, if a change occurs, stores the new
voltage values.
However these limits will be lost and will require relearning
should a new TCU be installed, or the throttle calibration data
is cleared by the execution of a particular sequence, This last
instance depends on the installation, and reference should be
made to the Diagnostics Section of this manual. The relearning
will happen automaticallyNotice
Above figure of T.P.S. is for the diesel engine
which is installed on the injection pump.
Gear Position Sensor
The gear position sensor is incorporated in the inhibitor switch
mounted on the side of the transmission case.
(Refer to figure 3.5.) The gear position sensor is a multi-function
switch providing three functions:
lInhibit starting of the vehicle when the shift lever is in a
position other than Park or Neutral
lIlluminate the reversing lamps when Reverse is
selected indicate to the TCU which lever position has
been selected by way of a varying resistance (Refer to
table 3.3.)
Figure 3.5 - Inhibitor Switch

AUTOMATIC TRANSMISSION 5A-27
Shift Lever Position
Manual 1
Manual 2
Manual 3
Drive
Netural
Reverse
ParkResistance (OHMS)
1k - 1.4k
1.8k - 2.2k
3k - 3.4k
4.5k - 4.9k
6.8k - 7.2k
10.8k - 11.2k
18.6k - 19k
Table 3.3 - Readings for Resistance/Shift Lever Positions
Diagnostics Inputs
The diagnostics control input or K-line is used to initiate the outputting of diagnostics data from the TCU to a diagnostic
test instrument. This input may also be used to clear the stored fault history data from the TCU’s
retentive memory. Connection to the diagnostics input of the TCU is via a connector included in the vehicle’s wiring
harness or computer interface. Refer to the vehicle manufacturer’s manual for the location of the self test
connectors.
Battery Voltage Monitoring Input
The battery voltage monitoring input connects to the positive side of the battery. The signal is taken from the
main supply to the TCU.
If operating conditions are such that the battery voltage at the TCU falls below 11.3V the transmission will adopt a ‘low
voltage’ mode of operating in which shifts into first gear are inhibited. All other shifts are allowed but may not occur
because of the reduced voltage. This condition normally occurs only when the battery is in poor condition.
When system voltage recovers, the TCU will resume normal operation after a 3 second delay period.
TCU Outputs
The outputs from the TCU are supplied to the components described below:
Solenoids
The TCU controls seven solenoids. Solenoids 1 to 6 (S1 to S6) are mounted in the valve body, while Solenoid 7 (S7)
is mounted in the pump cover. The normal state (OPEN/CLOSED) and the functions associated with the solenoids
are detailed in table 3.4. Table 3.5 details the S1 and S2 logic for static gear states. The logic during gear changes for
S1 to S4 and S7 is detailed in table 3.6.

5A-28 AUTOMATIC TRANSMISSION
Table 3.4 - Solenoid States and Functions
Table 3.5 - Solenoid Logic for Static Gear States
Solenoids 1 and 2
Solenoids 3 and 4
Solenoid 5
Solenoid 6
Solenoid 7S1 and S2 are normally open On/off solenoids that set the selected gear.
These solenoids determine static gear position by operating the shift valves.
Refer to table 3.5. Note that S1 and S2 solenoids also send signal pres-
sure to allow or prohibit rear band engagement.
S3 and S4 are normally open On/off solenoids that combine to control
shift quality and sequencing. S3 switches the clutch regulator valve off or
on. S4 switches the front band regulator valve off or on.
S5 is a variable force solenoid that ramps the pressure during gear
changes. This solenoid provides the signal pressure to the clutch and
band regulator, thereby controlling the shift pressures.
S6 is a normally open On/off solenoid that sets the high/low level of line
pressure, Solenoid off gives high pressure.
S7 is a normally open On/off solenoid that controls the application of the
converter clutch. Solenoid on activates the clutch.
S2
ON
ON
OFF
OFF
OFF
OFF
OFFS1
ON
OFF
OFF
ON
OFF
OFF
OFF Gear
1st
2nd
3rd
4th
Reverse
Neutral
Park

AUTOMATIC TRANSMISSION 5A-29
Table 3.6- Solenoid Operation During Gearshifts
To Initiate Shift
S1 OFF
S4 ON
S1 OFF
S2 OFF
S3 ON
S4 ON
S2 OFF
S3 ON
S4 ON
S2 OFF
S3 ON
S4 ON
S1 ON
S4 ON
S4 ON
S3 ON
S3 ON
S4 ON
S2 ON
S4 ON
S3 ON
S4 ON
S4 ON
S7 ONTo Complete Shift
S4 OFF
S3 OFF
S4 OFF
S3 OFF
S4 OFF
S3 OFF
S4 OFF
S4 OFF
S1 OFF
S4 OFF
S1 OFF
S2 ON
S3 OFF
S2 ON
S3 OFF
S4 OFF
S4 OFF
S1 ON
S2 ON
S3 OFF
S4 OFF
S1 ON
S4 OFF
S7 OFFTypical S5 Current Ramp
750mA to 600mA
850mA to 750mA
850mA to 750mA
700mA to 500mA
750mA to 600mA
750mA to 900mA
750mA to 950mA
600mA to 1000mA
600mA to 450mA @ 20 kph.
550mA to 400mA @ 60 kph.
800mA to 650mA @ 100 kph.
700mA to 950mA
800mA to 950mA
700mA to 400mA
600mA to 100mA Shift
1-2
1-3
1-4
2-3
3-4
4-3
4-2
4-1
3-2
3-1
2-1
Conv. Clutch
ON
OFF

5A-30 AUTOMATIC TRANSMISSION
Solenoid Valve Symbols (On/off Solenoids)
The solenoid symbol shown adjacent to each solenoid on the
hydraulic system schematics indicates the state of the oil flow
through the solenoid valve with the power On or 0ff. Refer to
figure 3.6 for the On/off operational details of NO solenoid
valves.
Normally Open (NO) Solenoid
POWER ON
Line 500 port is closed. The output port is open to exhaust at
the solenoid valve.
POWER OFF
The exhaust port is closed. The output port is open to line 500,Figure 3.6- Normally Open (NO) Symbols
Variable Pressure Solenoid Multiplexing System
Friction element shifting pressures are controlled by the variable pressure solenoid (VPS).
Line pressure is completely independent of shift pressure and is a function of throttle position, gear state and engine
speed.
S5 is a proportional or variable pressure solenoid that provides the signal pressure to the clutch and band regulator
valves thereby controlling shift pressures.
VPS pressure is multiplexed to the clutch regulator valve, the band regulator valve and the converter clutch regulator
valve during automatic gearshifts.
A variable pressure solenoid produces a hydraulic pressure inversely proportional to the current applied. During a
gearshift the TCU applies a progressively increasing or decreasing (ramped) current to the solenoid. Current applied
will vary between a minimum of 200 mA and a maximum of 1000 mA, Increasing current decreases output (55)
pressure. Decreasing current increases output (55) pressure.
Line 500 pressure, (approximately 440 to 560 kPa), is the reference pressure for the VPS, and the VPS output
pressure is always below line 500 pressure.
When the VPS is at standby, that is no gearshift is taking place, the VPS current is set to 200 mA giving maximum
output pressure.
Under steady state conditions the band and clutch regulator valve solenoids are switched off. This applies full Line
500 pressure to the plunger and because Line 500 pressure is always greater than S5 pressure it squeezes the S5
oil out between the regulator valve and the plunger. The friction elements are then fed oil pressure equal to Line 500
multiplied by the amplification ratio.
When a shift is initiated the required On/off solenoid is switched on cutting the supply of Line 500 to the plunger.
At the same time the VPS pressure is reduced to the ramp start value and assumes control of the regulator valve by
pushing the plunger away from the valve. The VPS then carries out the required pressure ramp and the timed shift is
completed by switching Off the On/off solenoid and returning the VPS to the standby pressure.
This system enables either the band or clutch or both to be electrically controlled for each gearshift.
Mode Indicator Light
Depending on the application, the mode indicator light may be used to indicate the mode that has been selected or
if an overheat condition exists. The mode indicator light is usually located on the instrument cluster.
Communication Systems
CAN
The controller area network (CAN) connects various control modules by using a twisted pair of wires, to share
common information. This results in a reduction of sensors and wiring. Typical applications include using the engine
controller to obtain the actual engine speed and throttle position, and adding these to the network. The ABS controller
(if fitted) can be used to obtain the road speed signal. This information is then available to the TCU without any
additional sensors.

AUTOMATIC TRANSMISSION 5A-31
K-Line
The K-line is typically used for obtaining diagnostic information from the TCU. A computer with a special interface is
connected to the TCU and all current faults, stored faults, runtime parameters are then available. The stored fault
codes can also be cleared.
The K-line can be used for vehicle coding at the manufacturer’s plant or in the workshop. This allows for one TCU
design to be used over different vehicle models. The particular code is sent to the microprocessor via the K line and
this results in the software selecting the correct shift and VPS ramp parameters.
HYDRAULIC CONTROL SYSTEM
The hydraulic controls are located in the valve body, pump body and main case.
The valve body contains the following:
lManual valve,
lThree shift valves,
lSequence valve,
lsolenoid supply pressure regulator valve,
lline pressure control valve,
lclutch apply regulator valve,
lband apply regulator valve,
lS1 to S6, and
lReverse lockout valve.
lThe pump body contains the following:
lPrimary regulator valve for line pressure,
lconverter clutch regulator valve,
lconverter clutch control valve,
lS7,and
lC1 bias valve.
The main case contains the following:
lB1R exhaust valve
The hydraulic control system schematic is shown at figure 3.7.
All upshifts are accomplished by simultaneously switching on a shift valve(s), switching VPS pressure to the band
and/or clutch regulator valve, and then sending the VPS a ramped current. The shift is completed by switching the
regulators off and at the same time causing the VPS to reach maximum . pressure. All downshifts are accomplished
by switching VPS pressure to the band and/or clutch regulator valve and sending a ramped current to the VPS. The
shift is completed by simultaneously switching the regulators off, switching the shift valves and at the same time
causing the VPS to return to stand-by pressure.
The primary regulator valve is located in the pump cover and supplies four line pressures; high and low for forward
gears, and high and low for reverse. This pressure has no effect on shift quality and merely provides static clutch
capacity during steady state operation. Low pressure can be obtained by activating an On/off solenoid with high line
pressure being the default mode.
Torque converter lock-up is initiated by toggling the converter clutch control valve with an On/off solenoid. The actual
apply and release of the clutch is regulated by the VPS via the converter clutch regulator valve. As an additional
safety feature, the lock-up is hydraulically disabled in first and second gear by the bias valve which only supplies oil
to the lock-up solenoid when C1 is applied in third and fourth gears. This prevents the vehicle from being rendered
immobile in the unlikely event of S7 becoming stuck.
The solenoid supply valve provides reference pressure for all the solenoids.