2004 ISUZU TF SERIES low oil pressure

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Page 3962 of 4264

ISUZU TF SERIES 2004 Workshop Manual 7A1-16 CONSTRUCTION AND FUNCTION
Control Valve Fail-safe Function
To prevent interlocking due to engagement of more than three clutches and brakes at the same time, the
2-4 brake fail-safe valve

Page 3964 of 4264

ISUZU TF SERIES 2004 Workshop Manual 7A1-18 CONSTRUCTION AND FUNCTION
Terminal Assembly
Pin No. Connected to Connected TCMPin No.
6 Line Pressure Solenoid B23
12 Low & Reverse Brake Oil Pressure Switch B12
5 Low & Reverse Bra

Page 3971 of 4264

ISUZU TF SERIES 2004 Workshop Manual CONSTRUCTION AND FUNCTION 7A1-25
TRANSMISSION CONTROL MODULE (TCM)
The TCM is fitted side of brake pedal by means of two stud bolts.
The TCM judges necessary line pressure, gear shifting point

Page 3972 of 4264

ISUZU TF SERIES 2004 Workshop Manual 7A1-26 CONSTRUCTION AND FUNCTION
CONTROL MECHANISM
CONTENT OF FUNCTION AND CONTROL
Item Description
Line pressure control TCM issues a signal according to the vehicle traveling, engine load and o

7A1-26 CONSTRUCTION AND FUNCTION
CONTROL MECHANISM
CONTENT OF FUNCTION AND CONTROL
Item Description
Line pressure control TCM issues a signal according to the vehicle traveling, engine load and other conditions to
TCM and the ON/OFF type line pressure solenoid is driven to switch the line pressure to
high or low pressure.
The line pressure solenoid is switched to the low pressure side when the solenoid is turned
ON (power supplied) and to the high pressure side when turned OFF (no power supplied).
In the forward travel range (D, 3, 2, L range), the line pressure decreases lower than that in
the P, N, and R range through the oil pressure circuit for the forward travel range.

Gear shift control The TCM issues a shift solenoid drive signal based on the traveling mode switch, inhibitor
switch, vehicle speed, throttle opening and other input signal to control the optimum gear
position automatically.
Speed change features have been set up to the TCM; the normal mode is suited to usual
traveling and the power mode is appropriate when the vehicle is loaded or accelerates the
speed.
In addition, speed change features used only for high oil temperature, hill climbing, and
down have been set up to the TCM, which are automatically switched depending on the
traveling conditions.
When the oil temperature is low (below 10C), speed change from the third to the fourth
speed is prohibited by the gear shift control.

Shift pattern selection
control
According to a vehicle condition, the TCM selects the following shift pattern.

Selection Priority Shift Pattern 3rd Start Lamp Power Drive Lamp
High High Temperature OFF OFF
3rd Start ON
4L
Power SW Off
OFF
Down Slop Power SW On
Power ON
Up Slope
Low Normal
OFF
OFF

- High temperature mode -
High temperature mode setting condition
ATF temperature: More than 123C
Above condition is met for more than 10 seconds.
High temperature mode cancel condition
ATF temperature: Less than 116C
Above condition is met for more than 10 seconds.

- 3rd start mode -
3rd start mode setting condition
3rd start switch: On Off (Pushed)
Vehicle speed: Less than 11km/h
ATF temperature: Less than 115C
Throttle position: Less than 8%
Select lever position: D range
Above conditions are met at the same time.
3rd start mode reset condition
3rd start switch: On Off again(Pushed again)
Vehicle speed: More than 34km/h
Select lever position: Other than D range
At least, one of above conditions is met.

Page 3973 of 4264

ISUZU TF SERIES 2004 Workshop Manual CONSTRUCTION AND FUNCTION 7A1-27
Item Description
- 4L mode -
4L mode setting condition
4L switch: On
Vehicle speed: More than 5km/h
Above conditions are met at the same time.
4L mode reset c

CONSTRUCTION AND FUNCTION 7A1-27
Item Description
- 4L mode -
4L mode setting condition
4L switch: On
Vehicle speed: More than 5km/h
Above conditions are met at the same time.
4L mode reset condition
4L switch: Off
Vehicle speed: Less than 4km/h
Above conditions are met at the same time.

- Down slope mode -
Down slope mode setting condition
Brake switch: On
Engine idle condition: More than 2.5 seconds
Select lever position: D or 3 range
Vehicle speed: More than 55km/h
Vehicle speed change: More than 1km/h
Above conditions are met at the same time.
Down slope mode reset condition
Engine idle condition: Not idle condition
Select lever position: Other than D or 3 range
At least, one of above conditions is met.

- Power Mode -
When power drive switch is On at only D range or 3 range, the shift change is performed by
1 – 4 speed based on shift diagram set as power pattern.

- Up slope mode -
Up-slope reasoning value is calculated from the average throttle angle and the average
acceleration. Otherwise, up-slope reasoning value is calculated from the vehicle speed.
TCM judges as up-slope mode when the former is bigger than latter.

Lock-up control The lock-up solenoid adjusts the pressure based on the signal from the TCM according to
the vehicle speed, throttle opening and other input signals based on the pre-set lock-up
point to control the lock-up.
Smooth lock-up control engages and disengages the clutch smoothly at the time of lock-up.
When the oil temperature is low (below 20C) or high (above 128C), lock-up is prohibited
even when the vehicle is at a lock-up speed.
The lock-up is disengaged also when the throttle is closed.
Direct electronic shift
control (DESC)
The duty cycle type solenoid is used for each clutch and brake. The solenoid adjusts the
clutch pressure to be suited to the engine load and vehicle traveling condition based on the
signal from the TCM. The pressure switch provided in the control valve oil passage sends
the oil pressure condition to the TCM to control the disengagement and engagement of the
clutch and brake directly and finely.
Learning control Learning is controlled to correct the oil pressure control timing to engage or disengage the
clutch optimally in order to compensate changes of the engine performance and changes
of the transmission with time. It is controlled to bring the speed-change time closer to the
value pre-set to the TCM.

Page 3975 of 4264

ISUZU TF SERIES 2004 Workshop Manual CONSTRUCTION AND FUNCTION 7A1-29
CONTROL ITEM, INPUT AND OUTPUT

Control item

Item

Line
pressure
control
Gear
shift
control
Shift
pattern
selection
Lock-up
controlDirect
electr

Page 3976 of 4264

ISUZU TF SERIES 2004 Workshop Manual 7A1-30 CONSTRUCTION AND FUNCTION
LINE PRESSURE CONTROL
Either the throttle opening, vehicle speed, turbine rotational speed, ATF temperature or speed-change
range signal appropriate under the si

7A1-30 CONSTRUCTION AND FUNCTION
LINE PRESSURE CONTROL
Either the throttle opening, vehicle speed, turbine rotational speed, ATF temperature or speed-change
range signal appropriate under the situation is issued from the TCM. The ON/OFF type line pressure
solenoid is actuated and switches the line pressure to high or low pressure.
The line pressure generated by the oil pump acts on the point A of the pressure regulator valve. When
the pressure control solenoid is turned ON by the signal from the TCM, the solenoid pressure does not
act. The line pressure is adjusted to match the spring force acting on the right side of the pressure
regulator valve.
When the pressure control solenoid is turned OFF, the solenoid pressure acts so that the line pressure is
adjusted to match the spring force acting on the right side of the pressure regulator valve.
As a result, the line pressure is adjusted to be low when the pressure control solenoid is ON and to be
high when the pressure control solenoid is OFF.
In the D, 3, 2 and L range, the line pressure through the oil pressure circuit acts onto the point B of the
pressure regulator valve and the pressure regulator valve moves so as to increase the pressure to be
drained, so that the line pressure is adjusted to be lower than the P, N, and R range by the difference of
area at the point B.

Figure 50. Line Pressure Control

LOCK-UP CONTROL
The lock-up solenoid adjusts the pressure and controls the lock-up based on the pre-set lock-up point,
according to the vehicle speed, throttle opening, engine rotations, turbine rotations and ATF temperature
input signal, based on the signal from the TCM.
Smooth lock-up control is employed to engage or disengage the clutch smoothly at the time of lock-up.
When the oil temperature is low (below 20C) or high (over 128C), lock-up is disengaged even though
the vehicle is at the lock-up speed.
The lock-up is disengaged also when the throttle is closed.
When the TCM determines the lock-up engagement, the DUTY ratio to supply power to the lock-up
solenoid is gradually increased (5% to 95%) and the oil between the lock-up piston and converter cover is
gradually drained.
As a result, the lock-up piston is fitted slowly under pressure to the converter cover securing smooth lock-
up engagement.

Page 3977 of 4264

ISUZU TF SERIES 2004 Workshop Manual CONSTRUCTION AND FUNCTION 7A1-31

Figure 51. Lock-up Control

DIRECT ELECTRIC SHIFT CONTROL (DESC)
Feature
Based on the each switch signals (low & reverse brake pressure, 2-4 brake press

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