Service Manuals, User Guides, Schematic Diagrams or docs for : . Car Manuals Subaru Impreza 2001-2002.2004-2007 Approved Subaru Impreza 2004 WRX STi 08. MECHANISM AND FUNCTION 33. AUTOMATIC TRANSMISSION 12. Electrohydraulic Control System
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W1860BE.book Page 67 Tuesday, January 28, 2003 11:01 PM
ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
12.Electrohydraulic Control System
A: DESCRIPTION
The electrohydraulic control system for the transmission and transfer consists of various sensors
and switches, a transmission control module (TCM) and the hydraulic controlling units including so-
lenoid valves. The system controls the automatic transmission operation, including gear shifting,
lockup clutch operation, line pressure, automatic control pattern selection (Base and Power), and
gear-shift timing. It also controls the operation of the transfer clutch. The TCM determines vehicle
operating conditions from various input signals and controls a total of eight solenoids (shift sole-
noids 1 and 2, low clutch timing solenoid, 2-4 brake timing solenoid, line pressure duty solenoid,
lockup duty solenoid, transfer duty solenoid and 2-4 brake duty solenoid) by sending appropriate
signals to them.
4AT-67
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
INPUT OUTPUT
ON-OFF
Throttle position sensor Shift solenoid 1
ON-OFF
Rear vehicle speed sensor Shift solenoid 2
Line pressure duty solenoid
Front vehicle speed sensor
ECM
Dropping resistor A (non-turbo model)
Engine speed signal
Lock-up duty solenoid
ATF temperature sensor
Transfer duty solenoid
Inhibitor switch
ECM 2-4 brake duty solenoid
Intake manifold pressure signal
(non-turbo model)
ECM Dropping resistor B (non-turbo model)
Mass air flow signal (turbo model) TCM
2-4 brake timing solenoid
FWD switch (non-turbo model)
Low clutch timing solenoid
Battery voltage ECM
Torque control signal 1
ECM
ABS signal
Torque control signal 2
ECM
Brake switch
AT diagnosis signal
Combination
Torque converter turbine speed sensor meter
FWD indicator light (non-turbo model)
ECM
Torque control cut signal AT OIL TEMP light
Cruise control signal Speedometer circuit
AT-00869
4AT-68
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
B: INPUT SIGNALS
Signal name Major function
Throttle position sensor Indicates the throttle valve position. This signal is used to determine shift point, line pres-
sure, and lockup engaging vehicle speed, which vary with engine load.
Front vehicle speed sensor Indicates the vehicle speed. This signal is used for control of gear shifting, lockup engag-
(located on transmission case) ing, line pressure, and transfer clutch operation.
Rear vehicle speed sensor (located on Used to control transfer clutch, and also as backup signal in case of failure of front vehicle
extension case) speed sensor.
Engine speed signal Indicates the engine speed. This signal is used for control of lockup clutch to ensure
smooth engagement.
Inhibitor switch Used to determine gears and line pressures in each of ranges P, R, N, D, 3, 2 and 1.
ATF temperature sensor Indicates the ATF temperature. This signal is used for inhibition of lockup, release of OD
and determination of ATF temperature.
FWD switch (SOHC models) Used for changing the mode from AWD to FWD. Also used for adapting the vehicle to
FWD tester roller. Changeover from AWD to FWD can be made by inserting a fuse into
the fuse holder.
ABS signal Used when ABS is operating to optimize ABS control. In this control, transfer clutch
torque load capacity is adjusted to eliminate the influence of engine braking and reduce
the degree of coupling between front and rear wheels.
Cruise control signal Indicates operation of cruise control system. It is used to expand 4th operating range.
Torque converter turbine speed sensor Tells the rotation speed of the input shaft. The proportion of this speed to the vehicle
speed determines whether shifting should be made or not.
Torque control cut signal Sent from engine control module (ECM) to TCM to temporarily inhibit the torque control
when starting off with low coolant temperature.
Intake manifold pressure signal (SOHC Used to determine line pressure of gear shifting.
models)
Mass air flow signal (DOHC turbo mod- Used to determine line pressure of gear shifting.
els)
Brake switch If this signal is issued during downhill driving, TCM makes downshift control, causing the
vehicle speed to be reduced.
4AT-69
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
C: OUTPUT SIGNALS
Signal name Function
Shift solenoid 1 and 2 Each of these signals controls gear speed by turning the corresponding solenoid ON/
OFF. Activating timing is controlled for each solenoid to reduce shift shock.
Line pressure duty solenoid Regulates the line pressure according to driving conditions.
Lockup duty solenoid Regulates the hydraulic pressure of the lockup clutch to operate it in three modes (open,
smooth and lockup).
Transfer duty solenoid Regulates the hydraulic pressure of the transfer clutch to control the driving force to the
rear drive shaft.
AT OIL TEMP light Causes the light to illuminate when ATF becomes excessively hot (exceeds a set temper-
ature level). This light is also used to display diagnostic trouble codes for the on-board
diagnosis function.
2-4 brake duty solenoid Regulates 2-4 brake operating pressure to reduce shifting shocks.
2-4 brake timing solenoid Switches on or off the pressure acting on 2-4 brake timing valve B to control the release
timing of the 2-4 brake.
Low-clutch timing solenoid Switches on or off the pressure acting on the low clutch timing valve B to control the re-
lease timing of the low clutch. Also switches on or off the pressure acting on the reverse
inhibit valve to control the reverse inhibit function.
Torque control signal 1 Reduces engine torque during range selection and gear change.
Torque control signal 2 Reduces engine torque during range selection and gear change.
4AT-70
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
D: CONTROL ITEMS
1. MPT MODELS
Control items Description of control
Transmission con- Shifting con- Base shift control Upshifting and downshifting are set for each range, gear and pattern ac-
trol trol Base pattern cording to throttle position and vehicle speed.
Power pattern
ABS-in-operation Gear speed is determined according to vehicle speed when ABS signal
control and brake signal is input.
ATF low tempera- Shifting into 4th gear is prevented when ATF temperature is below the
ture control preset value.
Automatic pat- Power pattern con- Power pattern is selected when throttle opening is changed at a speed
tern select trol exceeding the preset value.
control
Base pattern con- When throttle opening is changed at a speed less than the preset value,
trol Base pattern is resumed.
Lockup control Base lockup con- Lockup ON is set for D-range 4th gear; ON/OFF is set for all gears (ex-
trol cept D-range 4th) and patterns. Lockup control is performed according
to throttle position and vehicle speed. (Basically lockup is OFF during
gear shifting.)
Smooth control Smooth lockup is performed when lockup is switched on.
Line-pressure Ordinary control Line pressure is regulated according to throttle position, vehicle speed
control and range signals.
Shifting control Line pressure is regulated when shifting to lessen shifting shock.
Starting control Line pressure is lowered to a minimum so as to reduce engine cranking
load.
Shift timing Gear speed control ON/OFF timing for shift solenoid is controlled.
control
Lockup control When shifting, the lockup clutch is temporarily released.
Line-pressure con- When shifting, line pressure is controlled to the optimum level so as to
trol reduce shifting shock.
AWD transfer Ordinary transfer control Transfer clutch pressure is regulated according to the throttle valve an-
clutch control gle and vehicle speed.
1 range control Transfer clutch pressure is increased.
Slip control Immediately after detecting a slip, transfer clutch pressure is controlled
to the same pressure as 1 range. (This control is canceled if V 60 km/
h (37 MPH), or when throttle valve is closed fully.)
Turning control Transfer clutch pressure is reduced after detecting a turn.
ABS-in-operation control Transfer clutch pressure is adjusted to a set level immediately after re-
ception of ABS signal.
4AT-71
W1860BE.book Page 72 Tuesday, January 28, 2003 11:01 PM
ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
2. VTD MODELS
Control items Description of control
Transmission con- Shifting con- Base shift control Upshifting and downshifting are set for each range, gear and pattern ac-
trol trol Base pattern cording to throttle position and vehicle speed.
Power pattern
ABS-in-operation Gear speed is determined according to vehicle speed when ABS signal
control and brake signal is input.
ATF low tempera- Shifting into 4th gear is prevented when ATF temperature is below the
ture control preset value.
Automatic pat- Power pattern con- Power pattern is selected when throttle opening is changed at a speed
tern select trol exceeding the preset value.
control
Base pattern con- When throttle opening is changed at a speed less than the preset value,
trol Base pattern is resumed.
Lockup control Base lockup con- Lockup ON is set for D-range 4th gear; ON/OFF is set for all gears (ex-
trol cept D-range 4th) and patterns. Lockup control is performed according
to throttle position and vehicle speed. (Basically lockup is OFF during
gear shifting.)
Smooth control Smooth lockup is performed when lockup is switched on.
Line-pressure Ordinary control Line pressure is regulated according to throttle position, vehicle speed
control and range signals.
Shifting control Line pressure is regulated when shifting to lessen shifting shock.
Starting control Line pressure is lowered to a minimum so as to reduce engine cranking
load.
Shift timing Gear speed control ON/OFF timing for shift solenoid is controlled.
control
Lockup control When shifting, the lockup clutch is temporarily released.
Line-pressure con- When shifting, line pressure is controlled to the optimum level so as to
trol reduce shifting shock.
AWD multi-plate Ordinary transfer control Multi-plate clutch (LSD) pressure is regulated according to the torque
clutch (LSD) con- input to the transfer and the driving condition.
trol
Start control When starting, the LSD pressure is adjusted proportionately to the
throttle value angle.
Turning control When the front and rear wheel speed ratio is less than the set value for
a vehicle speed, the LSD pressure is decreased.
Slip control When a front or rear wheel starts slipping, the LSD pressure is de-
creased.
ABS-in-operation control The LSD pressure is adjusted to the set level immediately after recep-
tion of ABS signal.
Base brake control When the brake switch is ON and throttle valve is fully closed, the LSD
pressure is lowered.
1 range control The LSD pressure is increased to improve driveability.
4AT-72
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
E: THROTTLE POSITION SENSOR
The throttle position sensor provides electrical signals corresponding to throttle valve positions. The
throttle valve angular position and accelerator depressing speed are detected by this throttle posi-
tion sensor.
4AT-73
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
F: REAR VEHICLE SPEED SENSOR
1. MPT MODELS
This vehicle speed sensor (output shaft speed sensor) is externally mounted on the extension case.
It detects the rear wheel speed in terms of the peripheral speed of the transfer clutch drum and
sends sine wave signals (30 pulses per rotation) to the TCM.
(1)
AT-00413
(1) Rear vehicle speed sensor
2. VTD MODELS
This vehicle speed sensor (output shaft speed sensor) is externally mounted on the extension case.
It detects the rear wheel speed in terms of the peripheral speed of the rear drive shaft and sends
sine wave signals (22 pulses per rotation) to the TCM.
(1)
AT-00732
(1) Rear vehicle speed sensor
4AT-74
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
G: FRONT VEHICLE SPEED SENSOR
This vehicle speed sensor (output shaft speed sensor) is externally mounted on the transmission
case. It detects the front wheel speed and sends sine wave signals (16 pulses per rotation) to the
TCM.
The TCM converts the signals into pulse signals and outputs them to both the engine control module
(ECM) and the combination meter.
MPT models
(1)
AT-00414
(1) Front vehicle speed sensor
VTD models
(1)
AT-00733
(1) Front vehicle speed sensor
4AT-75
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
H: ATF TEMPERATURE SENSOR
This sensor is integrated with the transmission harness and is mounted on the hydraulic control
valve body of the transmission. It detects the temperature of ATF and outputs it as an electrical re-
sistance signal. The output characteristics of the sensor are shown below.
(A)
(B)
(1) AT-00415
(1) ATF temperature sensor (A) Resistance (B) Temperature
I: TORQUE CONVERTER TURBINE SPEED SENSOR
The torque converter turbine speed sensor (output shaft speed sensor) is externally mounted on
the transmission case.
The sensor detects the torque converter turbine speed in terms of the rotation speed of the periph-
ery of the high clutch drum coupled to the input shaft, and sends sine wave signals (32 pulses per
rotation) to the TCM. The TCM calculates the proportion of the input shaft speed to the vehicle
speed and determines whether the shifting is to be made or not.
(1)
AT-00416
(1) Torque converter turbine speed sensor
4AT-76
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
J: INHIBITOR SWITCH
The inhibitor switch assures safety when starting the engine. This switch is mounted on the right
side of the transmission case, and is operated by the selector lever.
When the selector lever is set to P or N, the electrical circuit in the inhibitor switch is closed and the
starter circuit is completed for cranking the engine.
When the selector lever is in the R, D, 3, 2 or 1 range, the electrical circuit in the inhibitor switch is
open. Hence engine cranking is disabled. In the R range, the backup light circuit is completed in the
switch, and the backup lights come on.
In addition to the above function, the inhibitor switch incorporates a circuit for detecting the selected
range position and sending the range signal to the TCM.
Inhibitor switch side connector
(4) (3) (2) (1)
(8) (7) (6) (5)
(12) (11) (10) (9)
AT-00417
Range position Pin No.
P (4) -- (3)
(12) -- (11)
R (4) -- (2)
(10) -- (9)
N (4) --(1)
(12) -- (11)
D (4) -- (8)
3 (4) -- (7)
2 (4) -- (6)
1 (4) -- (5)
4AT-77
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
K: SHIFT SOLENOIDS 1 AND 2
These solenoids are mounted on the transmission hydraulic control valve body. They are turned ON
or OFF according to signals from the TCM. The gear positions are changed according to the ON
and OFF condition of these solenoids.
(1)
(2)
AT-00418
(1) Shift solenoid 2
(2) Shift solenoid 1
L: LOW-CLUTCH TIMING SOLENOID
This solenoid is mounted on the transmission hydraulic control valve body. It is turned ON or OFF
according to signals from the TCM. It then controls the low clutch timing valve B and reverse inhibitor
valve.
(1)
AT-00419
(1) Low-clutch timing solenoid
4AT-78
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ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
M: 2-4 BRAKE TIMING SOLENOID
This solenoid is mounted on the transmission hydraulic control valve body. It is turned ON or OFF
according to signals from the TCM. It then controls the 2-4 brake timing valve B to decrease the
change gear shock.
(1)
AT-00420
(1) 2-4 brake timing solenoid
N: LINE PRESSURE DUTY SOLENOID
This solenoid is mounted on the transmission hydraulic control valve body. Its duty ratio is controlled
by signals from the TCM. This solenoid then controls the pressure modifier valve and accumulator
control valve A to adjust the line pressure to an optimum pressure level suitable for operating con-
ditions.
(1)
AT-00421
(1) Line pressure duty solenoid
4AT-79
W1860BE.book Page 80 Tuesday, January 28, 2003 11:01 PM
ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
O: LOCKUP DUTY SOLENOID
This solenoid is mounted on the transmission hydraulic control valve body. Its duty ratio is controlled
by signals from the TCM. It then controls the lockup control valve to provide smooth engagement
and disengagement of the lockup clutch.
(1)
AT-00422
(1) Lockup duty solenoid
P: 2-4 BRAKE DUTY SOLENOID
This solenoid is mounted on the transmission hydraulic control valve body. Its duty ratio is controlled
by signals from the TCM. It modulates the 2-4 brake pressure when the 2-4 brake is operated, re-
ducing shifting shocks.
(1) AT-00423
(1) 2-4 brake duty solenoid
4AT-80
W1860BE.book Page 81 Tuesday, January 28, 2003 11:01 PM
ELECTROHYDRAULIC CONTROL SYSTEM
AUTOMATIC TRANSMISSION
Q: TRANSFER DUTY SOLENOID
This solenoid is mounted on the transfer hydraulic pressure control unit on the rear end of transmis-
sion case. Its duty ratio is controlled by signals from the TCM. It then controls the transfer clutch/
control valve to control the pressure applied to the transfer clutch.
MPT models
(1)
AT-00424
(1) Transfer duty solenoid
VTD models
(1) AT-00734
(1) Transfer duty solenoid
4AT-81
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