2001 INFINITI QX4 engine

SAT003J
Normal ControlNBAT0180S0101The line pressure to throttle opening characteristics is set for suit-
able clutch operation.
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Back-up Control (Engine brake)NBAT0180S0102If the selector lever is shifted to ª2º position while driving in D4(OD)
or D
3, great driving force is applied to the clutch inside the trans-
mission. Clutch operating pressure (line pressure) must be
increased to deal with this driving force.
SAT005J
During Shift ChangeNBAT0180S0103The 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 TemperatureNBAT0180S0104IFluid viscosity and frictional characteristics of the clutch facing
change with fluid temperature. Clutch engaging or band-con-
tacting pressure is compensated for, according to fluid
temperature, to stabilize shifting quality.
SAT006J
IThe line pressure is reduced below 60ÉC (140ÉF) to prevent
shifting shock due to low viscosity of automatic transmission
fluid when temperature is low.
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OVERALL SYSTEM
Control Mechanism (Cont'd)
AT-27

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ILine pressure is increased to a maximum irrespective of the
throttle opening when fluid temperature drops to þ10ÉC (14ÉF).
This pressure rise is adopted to prevent a delay in clutch and
brake operation due to extreme drop of fluid viscosity at low
temperature.
SHIFT CONTROLNBAT0180S02The shift is regulated entirely by electronic control to accommodate
vehicle speed and varying engine operations. This is accomplished
by electrical signals transmitted by the revolution sensor and
throttle position sensor. This results in improved acceleration per-
formance and fuel economy.
SAT008J
Control of Shift Solenoid Valves A and BNBAT0180S0201The TCM activates shift solenoid valves A and B according to sig-
nals from the throttle position sensor and revolution sensor 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 ªONº, the drain circuit closes and pilot pressure is applied to
the shift valve.
[Relation between shift solenoid valves A and B and gear positions]
Shift solenoid valveGear position
D
1,21,11D2,22,12D3D4(OD) N-P
A ON (Closed) OFF (Open) OFF (Open) ON (Closed) ON (Closed)
B ON (Closed) ON (Closed) OFF (Open) OFF (Open) ON (Closed)
Control of Shift Valves A and BNBAT0180S0202
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OVERALL SYSTEM
Control Mechanism (Cont'd)
AT-28

Torque Converter Clutch Control Valve OperationNBAT0180S0303
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Lock-up Released
The OFF-duration of the torque converter clutch solenoid valve is
long, and pilot pressure is high. The pilot pressure pushes the end
face of the torque converter clutch control valve in combination with
spring force to move the valve to the left. As a result, converter
pressure is applied to chamber A (torque converter clutch piston
release side). Accordingly, the torque converter clutch piston
remains unlocked.
Lock-up Applied
When the OFF-duration of the torque converter clutch solenoid
valve is short, pilot pressure drains and becomes low. Accordingly,
the control valve moves to the right by the pilot pressure of the
other circuit and converter pressure. As a result, converter pres-
sure is applied to chamber B, keeping the torque converter clutch
piston applied.
Also smooth lock-up is provided by transient application and
release of the lock-up.
OVERRUN CLUTCH CONTROL (ENGINE BRAKE
CONTROL)
NBAT0180S04Forward one-way clutch is used to reduce shifting shocks in down-
shifting 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.
Overrun Clutch Operating ConditionsNBAT0180S0401
Gear position Throttle opening
ªDº position D
1,D2,D3gear position
Less than 3/16
ª2º position 2
1,22gear position
ª1º position 1
1,12gear position At any position
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OVERALL SYSTEM
Control Mechanism (Cont'd)
AT-30

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Overrun Clutch Solenoid Valve ControlNBAT0180S0402The overrun clutch solenoid valve is operated by an ON-OFF sig-
nal transmitted by the TCM to provide overrun clutch control
(engine brake control).
When this solenoid valve is ªONº, the pilot pressure drain port
closes. When it is ªOFFº, the drain port opens.
During the solenoid valve ªONº pilot pressure is applied to the end
face of the overrun clutch control valve.
SAT049J
Overrun Clutch Control Valve OperationNBAT0180S0403When the solenoid valve is ªONº, pilot pressure A is applied to the
overrun clutch control valve. This pushes up the overrun clutch
control valve. The line pressure is then shut off so that the clutch
does not engage.
When the solenoid valve is ªOFFº, pilot pressure A is not gener-
ated. At this point, the overrun clutch control valve moves down-
ward by spring force. As a result, overrun clutch operation pressure
is provided by the overrun clutch reducing valve. This causes the
overrun clutch to engage.
In the ª1º position, the overrun clutch control valve remains pushed
down so that the overrun clutch is engaged at all times.
Control ValveNBAT0181FUNCTION OF CONTROL VALVENBAT0181S01
Valve name Function
IPressure regulator valve
IPressure regulator plug
IPressure regulator sleeve plugRegulate oil discharged from the oil pump to provide optimum line pressure for all
driving conditions.
Pressure modifier valve Used as a signal supplementary valve to the pressure regulator valve. Regulates
pressure-modifier pressure (signal pressure) which controls optimum line pressure for
all driving conditions.
Modifier accumulator piston Smooths hydraulic pressure regulated by the pressure modifier valve to prevent pul-
sations.
Pilot valve Regulates line pressure to maintain a constant pilot pressure level which controls
lock-up mechanism, overrun clutch, 3-2 timing required for shifting.
Accumulator control valve
Accumulator control sleeveRegulate 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.
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OVERALL SYSTEM
Control Mechanism (Cont'd)
AT-31

Valve name Function
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 up-shifting (1st,2nd,3rd,4th gears/4th
,3rd,2nd,1st gears) in combination with shift valve B.
Shift valve B Simultaneously switches three oil circuits using output pressure of shift solenoid valve
B in relation to driving conditions (vehicle speed, throttle opening, etc.).
Provides automatic downshifting and up-shifting (1st,2nd,3rd,4th gears/4th
,3rd,2nd,1st gears) in combination with shift valve A.
Shuttle shift valve S Switches hydraulic circuits to provide 3-2 timing control and overrun clutch control in
relation to the throttle opening.
Inactivates the overrun clutch to prevent interlocking in 4th gear when the throttle is
wide open.
Overrun clutch control valve Switches hydraulic circuits to prevent engagement of the overrun clutch simulta-
neously with application of the brake band in 4th gear. (Interlocking occurs if the
overrun clutch engages during D
4gear operation.)
4-2 relay valve Memorizes that the transmission is in 4th gear. Prevents the transmission from down-
shifting from 4th gear to 3rd and then to 2nd in combination with 4-2 sequence valve
and shift valves A and B when downshifting from 4th to 2nd gear.
4-2 sequence valve Prevents band servo pressure from draining before high clutch operating pressure
and band servo releasing pressure drain (from the same circuit) during downshifting
from 4th to 2nd gear.
Servo charger valve An accumulator and a one-way orifice are used in the 2nd gear band servo oil circuit
to dampen shifting shock when shifting from 1st to 2nd gear.
To maintain adequate flow rate when downshifting from 4th or 3rd gear to 2nd gear,
the servo charger valve directs 2nd gear band servo hydraulic pressure to the circuit
without going through the one-way orifice when downshifting from 3rd or a higher
gear.
3-2 timing valve Prevents a late operation of the brake band when shifting selector lever from ªDº to
ª1º or ª2º position while driving in D
3.
ª1º reducing valve Reduces low & reverse brake pressure to dampen engine-brake shock when down-
shifting from the ª1º position 2nd gear to 1st gear.
Overrun clutch reducing valve Reduces oil pressure directed to the overrun clutch and prevents engine-brake shock.
In ª1º and ª2º 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,
torque converter clutch control plug and
torque converter clutch control sleeveActivate or inactivate the lock-up function.
Also provide smooth lock-up through transient application and release of the lock-up
system.
Shuttle shift valve D Switches hydraulic circuits so that output pressure of the torque converter clutch sole-
noid valve acts on the lock-up valve in the ªDº position of 2nd, 3rd and 4th gears. (In
the ªDº position 1st gear, lock-up is inhibited.)
ILock-up control is not affected in ªDº position 2nd, 3rd or 4th gears, unless output
pressure of the torque converter clutch solenoid valve is generated by a signal
from the control unit.
OVERALL SYSTEM
Control Valve (Cont'd)
AT-32

IntroductionNBAT0014The A/T system has two self-diagnostic systems.
The first is the emission-related on board diagnostic system (OBD-II) performed by the TCM in combination
with the ECM. The malfunction is indicated by the MIL (malfunction indicator lamp) and is stored as a DTC in
the ECM memory but not the TCM memory.
The second is the TCM original self-diagnosis indicated by the O/D OFF indicator lamp. The malfunction is
stored in the TCM memory. The detected items are overlapped with OBD-II self-diagnostic items. For detail,
refer to AT-38.
OBD-II Function for A/T SystemNBAT0182The ECM provides emission-related on board diagnostic (OBD-II) functions for the A/T system. One function
is to receive a signal from the TCM used with OBD-related parts of the A/T system. The signal is sent to the
ECM when a malfunction occurs in the corresponding OBD-related part. The other function is to indicate a
diagnostic result by means of the MIL (malfunction indicator lamp) on the instrument panel. Sensors, switches
and solenoid valves are used as sensing elements.
The MIL automatically illuminates in One or Two Trip Detection Logic when a malfunction is sensed in rela-
tion to A/T system parts.
One or Two Trip Detection Logic of OBD-IINBAT0015ONE TRIP DETECTION LOGICNBAT0015S01If a malfunction is sensed during the first test drive, the MIL will illuminate and the malfunction will be stored
in the ECM memory as a DTC. The TCM is not provided with such a memory function.
TWO TRIP DETECTION LOGICNBAT0015S02When a malfunction is sensed during the first test drive, it is stored in the ECM memory as a 1st trip DTC
(diagnostic trouble code) or 1st trip freeze frame data. At this point, the MIL will not illuminate. Ð First Trip
If the same malfunction as that experienced during the first test drive is sensed during the second test drive,
the MIL will illuminate. Ð Second Trip
A/T-related parts for which the MIL illuminates during the first or second test drive are listed below.
ItemsMIL
One trip detection Two trip detection
Shift solenoid valve A Ð DTC: P0750 X
Shift solenoid valve B Ð DTC: P0755 X
Throttle position sensor or switch Ð DTC: P1705 X
Except aboveX
The ªtripº in the ªOne or Two Trip Detection Logicº means a driving mode in which self-diagnosis is performed
during vehicle operation.
OBD-II Diagnostic Trouble Code (DTC)NBAT0016HOW TO READ DTC AND 1ST TRIP DTCNBAT0016S01DTC and 1st trip DTC can be read by the following methods.
(
with CONSULT-II orGST)CONSULT-II or GST (Generic Scan Tool) Examples: P0705, P0710, P0720,
P0725, etc.
These DTCs are prescribed by SAE J2012.
(CONSULT-II also displays the malfunctioning component or system.)
I1st trip DTC No. is the same as DTC No.
IOutput of the diagnostic trouble code indicates that the indicated circuit has a malfunction.
However, in case of the Mode II and GST they do not indicate whether the malfunction is still
occurring or occurred in the past and returned to normal.
CONSULT-II can identify them as shown below. Therefore, using CONSULT-II (if available) is rec-
ommended.
A sample of CONSULT-II display for DTC and 1st trip DTC is shown on the next page. DTC or 1st trip DTC
of a malfunction is displayed in SELF-DIAGNOSTIC RESULTS mode for ªENGINEº with CONSULT-II. Time
data indicates how many times the vehicle was driven after the last detection of a DTC.
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ON BOARD DIAGNOSTIC SYSTEM DESCRIPTION
Introduction
AT-33

SAT014K
If the DTC is being detected currently, the time data will be ª0º.
SAT015K
If a 1st trip DTC is stored in the ECM, the time data will be ª1tº.
SAT016K
Freeze Frame Data and 1st Trip Freeze Frame DataNBAT0016S0101The ECM has a memory function, which stores the driving condition such as fuel system status, calculated
load value, engine coolant temperature, short term fuel trim, long term fuel trim, engine speed and vehicle
speed at the moment the ECM detects a malfunction.
Data which are stored in the ECM memory, along with the 1st trip DTC, are called 1st trip freeze frame data,
and the data, stored together with the DTC data, are called freeze frame data and displayed on CONSULT-II
or GST. The 1st trip freeze frame data can only be displayed on the CONSULT-II screen, not on the GST. For
detail, refer to EC-81, ªCONSULT-IIº.
Only one set of freeze frame data (either 1st trip freeze frame data of freeze frame data) can be stored in the
ECM. 1st trip freeze frame data is stored in the ECM memory along with the 1st trip DTC. There is no prior-
ity for 1st trip freeze frame data and it is updated each time a different 1st trip DTC is detected. However, once
freeze frame data (2nd trip detection/MIL on) is stored in the ECM memory, 1st trip freeze frame data is no
longer stored. Remember, only one set of freeze frame data can be stored in the ECM. The ECM has the fol-
lowing priorities to update the data.
ON BOARD DIAGNOSTIC SYSTEM DESCRIPTION
OBD-II Diagnostic Trouble Code (DTC) (Cont'd)
AT-34

Priority Items
1 Freeze frame data Misfire Ð DTC: P0300 - P0306
Fuel Injection System Function Ð DTC: P0171, P0172, P0174, P0175
2 Except the above items (Includes A/T related items)
3 1st trip freeze frame data
Both 1st trip freeze frame data and freeze frame data (along with the DTCs) are cleared when the ECM
memory is erased.
HOW TO ERASE DTCNBAT0016S02The diagnostic trouble code can be erased by CONSULT-II, GST or ECM DIAGNOSTIC TEST MODE as
described following.
IIf the battery terminal is disconnected, the diagnostic trouble code will be lost within 24 hours.
IWhen you erase the DTC, using CONSULT-II or GST is easier and quicker than switching the mode
selector on the ECM.
The following emission-related diagnostic information is cleared from the ECM memory when erasing DTC
related to OBD-II. For details, refer to EC-60, ªEmission-related Diagnostic Informationº.
IDiagnostic trouble codes (DTC)
I1st trip diagnostic trouble codes (1st trip DTC)
IFreeze frame data
I1st trip freeze frame data
ISystem readiness test (SRT) codes
ITest values
HOW TO ERASE DTC (WITH CONSULT-II)NBAT0016S03IIf a DTC is displayed for both ECM and TCM, it needs to be erased for both ECM and TCM.
1. If the ignition switch stays ªONº after repair work, be sure to turn ignition switch ªOFFº once. Wait at least
5 seconds and then turn it ªONº (engine stopped) again.
2. Turn CONSULT-II ªONº and touch ªA/Tº.
3. Touch ªSELF-DIAG RESULTSº.
4. Touch ªERASEº. (The DTC in the TCM will be erased.) Then touch ªBACKº twice.
5. Touch ªENGINEº.
6. Touch ªSELF-DIAG RESULTSº.
7. Touch ªERASEº. (The DTC in the ECM will be erased.)
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ON BOARD DIAGNOSTIC SYSTEM DESCRIPTION
OBD-II Diagnostic Trouble Code (DTC) (Cont'd)
AT-35