Cooling Strategy

AUTOMATIC GEARBOX - JATCO

DESCRIPTION AND OPERATION

44-45

HDC Mode
The HDC mode assists the ABS in controlling the descent of the vehicle in either 1st gear ratio or reverse gear ratio. 
HDC mode is initiated by selecting 1 or R on the selector lever, depressing the HDC button adjacent to the selector 
lever and throttle pedal released (low demand position). The instrument pack illuminates the HDC warning lamp and 
the LCD will display the selected gear (1 or R).

The EAT ECU will maintain the selected gear ratio and apply engine braking to assist the ABS in controlling the 
vehicle's descent.

Cruise Mode
Cruise control is activated by depressing the cruise control switch in the centre console. When cruise control is active, 
the EAT ECU senses this as a hardwired input from the interface unit. In cruise mode the EAT ECU uses a dedicated 
gearshift map to control the gearbox and assist in maintaining the set vehicle speed. The gearbox cruise mode is 
cancelled by applying the brake pedal or deselecting cruise control. Cruise mode is suspended when the throttle 
demand is increased and is reinstated when the pedal is released and the set speed resumed. Cruise mode is also 
suspended when the suspend switch on the steering wheel is pressed.

Reverse Inhibit
If the vehicle exceeds 6 mph (10 km/h) in the forward direction, and Reverse (R) gear is selected, the EAT ECU 
switches on the low clutch timing solenoid valve in the valve block, which drains the fluid from the reverse clutch.

This function prevents the gearbox from engaging reverse gear when the vehicle is moving in a forward direction, so 
preventing damage to the gearbox.

Hill Mode
Hill mode modifies the gearbox shift pattern to assist driveability on steep gradients. The EAT ECU detects the 
conditions to activate hill mode by monitoring the engine torque values, throttle angle and engine speed. This mode 
also assists driving at high altitudes and trailer towing.

Downhill Recognition
On downhill slopes there is a tendency for automatic gearboxes to upshift due to the increase in vehicle speed and 
the decrease in throttle angle.

The reduction in engine braking causes the driver to use the brakes. A downhill slope is recognised by EAT ECU as 
an increase in vehicle speed with the decrease in throttle angle.

When a downhill slope is recognised and the brakes are applied, the shift pattern is over-ruled and the gearbox shifts 
down a gear if engine speed allows. The downhill mode is cancelled upon application of the throttle.

Cooling Strategy
The purpose of the cooling strategy is to reduce engine and gearbox temperatures during high load conditions, for 
example when towing trailers. Under these conditions the engine and gearbox may generate excessive heat.

While in any gear other than 5th, or in 5th gear with the vehicle speed above 38 mph (61 km/h), if the gearbox fluid 
temperature increases to 127

°

C (260

°

F), the EAT ECU employs the cooling strategy.

This strategy consists of a separate shift and torque converter lock-up map that allows torque converter lock-up or 
gear changes to occur outside of their normal operating parameters.

This will reduce either the engine speed or the slip in the torque converter, therefore reducing the heat generated.

The EAT ECU cancels the cooling strategy when gearbox fluid temperature decreases to 120

°

C (248

°

F).