CommandShift JATCO Automatic Gearbox (page 2 of 3)

AUTOMATIC GEARBOX - JATCO

DESCRIPTION AND OPERATION

44-9

Valve Block and Solenoid Valves
Refer to JATCO Automatic Gearbox - Valve Block and Solenoids illustration.

The gearbox uses nine solenoid valves located on the valve block. The solenoid valves are energised/de-energised 
by the EAT ECU to control the gearbox fluid flow around the gearbox to supply clutches, brakes and brake band (gear 
change scheduling), fluid to the torque converter, lubrication and cooling.

Each solenoid valve is controlled separately by the EAT ECU. All nine solenoid valves can be classified into two types 
by their operating mode. Three of them are duty solenoid valves and the remaining six are on-off solenoid valves.

Each solenoid valve consists of an internal coil and needle valve. A voltage is passed through the coil of the solenoid 
to actuate the needle valve. The needle valve opens and closes the fluid pressure circuits. On-off solenoid valves 
close the fluid pressure circuits in response to current flow.

Duty solenoid valves repeatedly turn on and off in 50 Hz cycles. This opens and closes the fluid circuits allowing a 
higher level of control on the circuits. For example, smooth operation of the lock-up clutch in the torque converter to 
eliminate harsh engagement/ disengagement.

All of the solenoid valves are supplied with battery voltage and an earth path by the EAT ECU.

On/Off Solenoid Valves
The on/off solenoid valves are:

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Shift solenoid valve A

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Shift solenoid valve B

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Shift solenoid valve C

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Low clutch timing solenoid valve

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Reduction timing solenoid valve

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2-4 brake timing solenoid valve.

The EAT ECU switches the on/off solenoid valves to open and close in response to vehicle speed and throttle 
opening.  

Shift solenoid valves A, B and C are used to engage the different gear ratios within the gearbox. The position of these 
solenoid valves at any one time determines the gear selected.

Shift Solenoid Valve Activation

The reduction timing solenoid valve, low clutch timing solenoid valve and 2-4 timing solenoid valve are used by the 
EAT ECU to control the timing of the gear shift changes.

These solenoid valves carry out three main functions:

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Shift timing control: For some shifts these three solenoid valves are used to assist line pressure control or 2-4 
brake pressure control.

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Line pressure cut back: When the gearbox takes up the drive there should be a high line pressure present. The 
EAT ECU controls the low clutch timing solenoid valve which is related to the vehicle speed in order to switch the 
fluid circuit of the line pressure to on or off therefore controlling cut back.

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Reverse inhibition: If the vehicle exceeds 6 mph (10 km/h) and Reverse (R) is selected, the EAT ECU switches 
the low clutch timing solenoid valve on. This drains the gearbox fluid from the reverse clutch, therefore the clutch 
will be unable to engage.

Shift Solenoid Valve

1st Gear

2nd Gear

3rd Gear

4th Gear

5th Gear

A

X

O

X

X

O

B

O

O

O

X

X

C

O

X

X

O

O

X = Solenoid Valve Off

O = Solenoid Valve On