2008 NISSAN LATIO service

A/T CONTROL SYSTEM
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TCM FunctionINFOID:0000000001703163
The function of the TCM is to:
• Receive input signals sent from various switches and sensors.
• Determine required line pressure, shifting point, lock-up operation, and engine brake operation.
• Send required output signals to the respective solenoids.
CONTROL SYSTEM OUTLINE
The automatic transaxle senses vehicle operating conditions through various sensors or signals. It always
controls the optimum shift position and reduces shifting and lock-up shocks.
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SWITCHES & SENSORS
⇒TCM
⇒ACTUATORS
PNP switch
Accelerator pedal position signal
Closed throttle position signal
Wide open throttle position signal
Engine speed signal
A/T fluid temperature sensor
Revolution sensor
Turbine revolution sensor (Power
train revolution sensor)
Vehicle speed sensor
Overdrive control switch signal
Stop lamp switch signalShift control
Line pressure control
Lock-up control
Overrun clutch control
Fail-safe control
Self-diagnosis
CONSULT-III communication
line controlShift solenoid valve A
Shift solenoid valve B
Overrun clutch solenoid valve
Torque converter clutch solenoid
valve
Line pressure solenoid valve
OD OFF indicator lamp

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A/T CONTROL SYSTEM
CONTROL SYSTEM DIAGRAM
CAN CommunicationINFOID:0000000001703164
SYSTEM DESCRIPTION
CAN (Controller Area Network) is a serial communication line for real time application. It is an on-vehicle mul-
tiplex communication line with high data communication speed and excellent error detection ability. Many elec-
tronic control units are equipped onto a vehicle, and each control unit shares information and links with other
control units during operation (not independent). In CAN communication, control units are connected with 2
communication lines (CAN H line, CAN L line) allowing a high rate of information transmission with less wiring.
Each control unit transmits/receives data but selectively reads required data only. For details, refer to LAN-6,
"System Description".
Input/Output Signal of TCMINFOID:0000000001703165
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Control itemLine
pressure
controlVehicle
speed
controlShift
controlLock-up
controlEngine
brake
controlFail-safe
functionSelf-diag-
nostics
function
InputAccelerator pedal position signal
(*5)XXXXX(*3) XX
Vehicle speed sensor·A/T
(Revolution sensor)XXXXX(*3) XX
Vehicle speed sensor·MTR (*1) X (*1) X (*1) X (*1) X X
Closed throttle position signal
(*5)(*2) X (*2) X X X (*4) X
Wide open throttle position signal
(*5)(*2) X (*2) X (*4) X
Turbine revolution sensor (Power
train revolution sensor)XXXXX
Engine speed signal X X X X
PNP switch XXXXX(*3) X(*4) X
Stop lamp switch signal
(*5)XX (*4) X
A/T fluid temperature sensors
(*5)XXXX XX
Overdrive control switch signal
(*5)XXXX (*4) X
TCM power supply voltage signal X X X X

A/T CONTROL SYSTEM
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*1: Spare for vehicle speed sensor·A/T (revolution sensor)
*2: Spare for accelerator pedal position signal
*3: If these input and output signals are different, the TCM triggers the fail-safe function.
*4: Used as a condition for starting self-diagnostics; if self-diagnosis are not started, it is judged that there is some kind of error.
*5: Input by CAN communications.
*6: Output by CAN communications.
Line Pressure ControlINFOID:0000000001703166
• TCM has various line pressure control characteristics to match the driving conditions.
• An ON-OFF duty signal is sent to the line pressure solenoid valve based on TCM characteristics.
• Hydraulic pressure on the clutch and brake is electronically controlled through the line pressure solenoid
valve to accommodate engine torque. This results in smooth shift operation.
NORMAL CONTROL
The characteristic of the line pressure to the throttle opening is set
for suitable clutch operation.
BACK-UP CONTROL (ENGINE BRAKE)
If the selector lever is shifted to “2” position while driving in D4 or D3,
great driving force is applied to the clutch inside the transaxle. Clutch
operating pressure (line pressure) must be increased to deal with
this driving force.
DURING SHIFT CHANGE
Out-
putShift solenoid valve A/B X (*3) X X
Line pressure solenoid X (*3) X X
Torque converter clutch solenoid
valveX(*3) XX
Overrun clutch solenoid valve X X (*3) X X
OD OFF indicator lamp
(*6)XX Control itemLine
pressure
controlVeh icl e
speed
controlShift
controlLock-up
controlEngine
brake
controlFail-safe
functionSelf-diag-
nostics
function
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AT-30
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A/T CONTROL SYSTEM
The line pressure is temporarily reduced corresponding to a change
in engine torque when shifting gears (that is, when the shift solenoid
valve is switched for clutch operation) to reduce shifting shock.
AT LOW FLUID TEMPERATURE
• A/T fluid viscosity and frictional characteristics of the clutch facing change with A/T fluid temperature. Clutch
engaging or band-contacting pressure is compensated for, according to A/T fluid temperature, to stabilize
shifting quality.
• The line pressure is reduced below 60°C (140°F) to prevent shift-
ing shock due to high viscosity of A/T fluid when temperature is
low.
• Line pressure is increased to a maximum irrespective of the throt-
tle opening when A/T fluid temperature drops to −10°C (14°F). This
pressure rise is adopted to prevent a delay in clutch and brake
operation due to extreme drop of A/T fluid viscosity at low temper-
ature.
Shift ControlINFOID:0000000001703167
The shift is regulated entirely by electronic control to accommodate vehicle speed and varying engine opera-
tions. This is accomplished by electrical signals transmitted by the revolution sensor and the ECM (accelerator
pedal position sensor). This results in improved acceleration performance and fuel economy.
CONTROL OF SHIFT SOLENOID VALVES A AND B
The TCM activates shift solenoid valves A and B according to sig-
nals from the accelerator pedal position sensor and revolution sen-
sor to select the optimum gear position on the basis of the shift
schedule memorized in the TCM.
The shift solenoid valve performs simple ON-OFF operation. When
set to “ON”, the drain circuit closes and pilot pressure is applied to
the shift valve.
RELATION BETWEEN SHIFT SOLENOID VALVES A AND B AND GEAR POSITIONS
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A/T CONTROL SYSTEM
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CONTROL OF SHIFT VALVES A AND B
Pilot pressure generated by the operation of shift solenoid valves A and B is applied to the end face of shift
valves A and B.
The figure above shows the operation of shift valve B. When the shift solenoid valve is “ON”, pilot pressure
applied to the end face of the shift valve overcomes spring force, moving the valve upward.
Lock-up ControlINFOID:0000000001703168
The torque converter clutch piston in the torque converter is locked to eliminate torque converter slip and to
increase power transmission efficiency. The solenoid valve is controlled by an ON-OFF duty signal sent from
the TCM. The signal is converted to an oil pressure signal which controls the torque converter clutch piston.
CONDITIONS FOR LOCK-UP OPERATION
When vehicle is driven in 3rd and 4th gear positions, vehicle speed and throttle opening are detected. If the
detected values fall within the lock-up zone memorized in the TCM, lock-up is performed.
TORQUE CONVERTER CLUTCH SOLENOID VALVE CONTROL
Gear position 1 2 3 4
Shift solenoid valve A ON (Closed) OFF (Open) OFF (Open) ON (Closed)
Shift solenoid valve B ON (Closed) ON (Closed) OFF (Open) OFF (Open)
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OD ON OFF
Selector lever “D” position
Gear position D
4D3
Vehicle speed sensor More than set value
Accelerator pedal position signal Less than set opening
Closed throttle position signal OFF
A/T fluid temperature sensor More than 40°C (104°F)

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A/T CONTROL SYSTEM
Lock-up Control System Diagram
Lock-up Released
In the lock-up released state, the torque converter clutch control valve is set into the unlocked state by drain-
ing the torque converter clutch piston applying pressure and the torque converter clutch piston release pres-
sure is generated.
In this way, the torque converter clutch piston is not coupled.
Lock-up Applied
In the lock-up applied state, the torque converter clutch control valve is set into the locked state by generating
the torque converter clutch piston applying pressure and the torque converter clutch piston release pressure is
drained.
In this way, the torque converter clutch piston is pressed and coupled.
SMOOTH LOCK-UP CONTROL
When shifting from the lock-up released state to the lock-up applied state, the current output to the torque con-
verter clutch solenoid is controlled with the TCM. In this way, when shifting to the lock-up applied state, the
torque converter clutch is temporarily set to the half-clutched state to reduce the shock.
Half-clutched State
The current output from the TCM to the torque converter clutch solenoid is varied to steadily increase the
torque converter clutch solenoid pressure.
In this way, the lock-up applying pressure gradually rises and while the torque converter clutch piston is put
into half-clutched status, the torque converter clutch piston applying pressure is increased and the coupling is
completed smoothly.
Engine Brake Control (Overrun Clutch Control)INFOID:0000000001703169
Forward one-way clutch is used to reduce shifting shocks in downshifting operations. This clutch transmits
engine torque to the wheels. However, drive force from the wheels is not transmitted to the engine because
the one-way clutch rotates idle. This means the engine brake is not effective.
The overrun clutch operates when the engine brake is needed.
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A/T CONTROL SYSTEM
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OVERRUN CLUTCH OPERATING CONDITIONS
OVERRUN CLUTCH SOLENOID VALVE CONTROL
The overrun clutch solenoid valve is operated by an ON-OFF signal
transmitted by the TCM to provide overrun clutch control (engine
brake control).
When this solenoid valve is “ON”, the pilot pressure drain port
closes. When it is “OFF”, the drain port opens.
During the solenoid valve “ON” pilot pressure is applied to the end
face of the overrun clutch control valve.
OVERRUN CLUTCH CONTROL VALVE OPERATION
When the solenoid valve is “ON”, pilot pressure is applied to the
overrun clutch control valve. This pushes up the overrun clutch con-
trol valve. The line pressure is then shut off so that the clutch does
not engage. Only in “1” position, however, 1 range pressure is
applied to overrun clutch control valve, resulting in valve moving
downward and clutch engaged.
When the solenoid valve is “OFF”, pilot pressure is not generated. At
this point, the overrun clutch control valve moves downward by
spring force. As a result, overrun clutch operation pressure is pro-
vided by the overrun clutch reducing valve. At overrun clutch reduc-
ing valve in “D” position, the hydraulic pressure is reduced to a level
that balances the spring force. This is sent to overrun clutch control
valve and becomes the operating pressure of overrun clutch which is
engaged at all times. In “2” position and “1” position, overrun clutch
reducing valve is pushed down by 2 range pressure. Line pressure is
directly sent to overrun clutch control valve and becomes the operat-
ing pressure of overrun clutch which is engaged at all times.
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AT-34
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A/T CONTROL SYSTEM
Control Valve
INFOID:0000000001703170
FUNCTION OF CONTROL VALVES
Centrifugal Cancel MechanismINFOID:0000000001703171
FUNCTION
The centrifugal cancel mechanism is a mechanism to cancel the centrifugal hydraulic pressure instead of the
conventional check balls. It cancels the centrifugal hydraulic pressure which is generated as high clutch drum
rotates, and it allows for preventing high clutch from dragging and for providing stable high clutch piston press-
ing force in all revolution speeds.
STRUCTURE/OPERATION
Valve name Function
Pressure regulator valve, plug and sleeve
plugRegulates oil discharged from the oil pump to provide optimum line pressure for all driving
conditions.
Pressure modifier valve and sleeve Used as a signal supplementary valve to the pressure regulator valve. Regulates pres-
sure-modifier pressure (signal pressure) which controls optimum line pressure for all driv-
ing conditions.
Pilot valve Regulates line pressure to maintain a constant pilot pressure level which controls lock-up
mechanism, overrun clutch, shift timing.
Accumulator control valve Regulates accumulator back-pressure to pressure suited to driving conditions.
Manual valve Directs line pressure to oil circuits corresponding to select positions.
Hydraulic pressure drains when the shift lever is in Neutral.
Shift valve A Simultaneously switches three oil circuits using output pressure of shift solenoid valve A
to meet driving conditions (vehicle speed, throttle opening, etc.).
Provides automatic downshifting and upshifting (1st → 2nd → 3rd → 4th gears/4th → 3rd
→ 2nd → 1st gears) in combination with shift valve B.
Shift valve B Simultaneously switches two oil circuits using output pressure of shift solenoid valve B in
relation to driving conditions (vehicle speed, throttle opening, etc.).
Provides automatic downshifting and upshifting (1st → 2nd → 3rd → 4th gears/4th → 3rd
→ 2nd → 1st gears) in combination with shift valve A.
Overrun clutch control valve Switches hydraulic circuits to prevent engagement of the overrun clutch simultaneously
with application of the brake band in D
4. (Interlocking occurs if the overrun clutch engages
during D
4.)
1st reducing valve Reduces low & reverse brake pressure to dampen engine-brake shock when downshift-
ing from the 1st position 1
2 to 11.
Overrun clutch reducing valve Reduces oil pressure directed to the overrun clutch and prevents engine-brake shock.
In the 1st and 2nd positions, line pressure acts on the overrun clutch reducing valve to
increase the pressure-regulating point, with resultant engine brake capability.
Torque converter relief valve Prevents an excessive rise in torque converter pressure.
Torque converter clutch control valve, plug
and sleeveActivates or inactivates the lock-up function.
Also provides smooth lock-up through transient application and release of the lock-up
system.
1-2 accumulator valve and piston Lessens the shock find when the 2nd gear band servo contracts, and provides smooth
shifting.
3-2 timing valve Switches the pace that oil pressure is released depending on vehicle speed; maximizes
the high clutch release timing, and allows for soft downshifting.
Shuttle valve Determines if the overrun clutch solenoid valve should control the 3-2 timing valve or the
overrun clutch control valve and switches between the two.
Cooler check valve At low speeds and with a small load when a little heat is generated, saves the volume of
cooler flow, and stores the oil pressure for lock-up.