L322 Range Rover System Description and Operation
AUTOMATIC TRANSMISSION – ZF 5HP24
44-2-50 DESCRIPTION AND OPERATION
Engine Warm-Up Mode
The EAT ECU monitors the output from the transmission fluid temperature sensor in the transmission and also
receives an ECT sensor signal from the ECM on the CAN. When the transmission fluid and/or the engine coolant
temperature is less than 60
°
C (140
°
F), the EAT ECU initiates the shift maps used in sport mode, when driving after
a cold start.
The sport mode shift points raise the engine speed. This, in turn, promotes faster transmission fluid warm-up and also
decreases the warm-up time for the catalytic converter to reach optimum temperature.
The warm-up mode is terminated if the vehicle speed exceeds 37 mph (60 km/h), the transmission fluid or the engine
coolant temperature exceeds 60
°
C (140
°
F) or a maximum time of 3 minutes is exceeded.
HDC Mode
The HDC mode assists the ABS ECU in controlling the downhill speed of the vehicle. When HDC is selected on, the
EAT ECU selects the most appropriate gear for the descent, to maximise engine braking.
Cruise Mode
When cruise control is activated, the EAT ECU receives a cruise active message on the CAN. The EAT ECU activates
a cruise control map which prevents locking and unlocking of the torque converter clutch and minimises up and down
shifts. If cruise control is operative and the vehicle speed increases due to coasting downhill, the ECM can request a
down shift via a CAN message if the vehicle speed exceeds the set cruise limit.
Hill Mode
Hill mode is initiated by the EAT ECU when high engine torque, high throttle angle and low engine speed is detected
via ECM signals on the CAN. The EAT ECU defines this combination of signals to determine when the vehicle is
travelling on a steep gradient.
In hill mode the EAT ECU adopts one of three shift maps which hold the transmission in low gears throughout the
ascent. The shift map chosen depends on the severity of the slope as determined from the engine signals.
Hill mode can also be initiated when the vehicle is at very high altitudes.
Default (Limp Home) Mode
If a transmission fault is detected by the EAT ECU, the ECU adopts a limp home mode strategy. 'TRANS. FAILSAFE'
is displayed in the message centre and, if the fault has an effect on engine emissions, the MIL will also be illuminated.
In default mode, P, R and N functions operate normally (if the fault allows these selections) and the EAT ECU locks
the transmission in 4th gear to allow the driver to take the vehicle to the nearest dealer. The torque converter lock-up
clutch is disabled and reverse lock-out will not function.
If the vehicle is topped and subsequently restarted in the default mode condition, the EAT ECU operates normally
until the fault which caused the condition is detected again.
Reverse Lock-Out Mode
When the vehicle is travelling forwards, selecting reverse could cause transmission damage. To protect against this,
reverse gear is prohibited if the vehicle is travelling forwards at a road speed above 5 mph (8 km/h).
Cooling Strategy
The purpose of the cooling strategy is to reduce engine and transmission temperatures during high load conditions,
when towing a trailer for example. Under these conditions the engine and transmission may generate excessive heat.
If the transmission fluid temperature increases to 140
°
C (284
°
F) or higher, the EAT ECU employs the cooling strategy.
The strategy uses a specific shift and torque converter lock-up clutch map. This map allows torque converter clutch
lock-up and gear shifts to operate outside of their normal operation. This will reduce the engine speed and/or slip in
the torque converter, therefore reducing heat generated by the engine and the transmission.
The cooling strategy is cancelled when the transmission fluid temperature decreases to 130
°
C (266
°
F) or below.
