Jaguar XJ (X350). Service manual — part 1044
Transmission Shift selection
Shift Map Selection
The transmission control system utilizes a number of driver selectable operating modes and also a
number of adaptive/automatically selectable modes. Sport, Normal and Cruise Control mode are all
driver selectable. Hot mode, traction control mode and trailer towing mode are all adaptive modes
i.e. the transmission will automatically select this mode dependent upon the current driving
conditions.
Normal Mode
Normal mode can be selected by activation of the transmission mode switch located on the J-Gate.
Once activated this mode will remain engaged until the driver deselects the mode or engages the
cruise control system. If the driver engages cruise control when Normal mode is active upon
deactivation of the cruise system the transmission will automatically re-engage Normal mode. This
mode can be over-ridden by a number of adaptive modes.
The mode switch is of the momentary type.
Cruise Mode
When the driver engages the cruise control system the TCM receives a CAN message transmitted by
the Adaptive Cruise Control (ACC) or engine electronic controls which informs the TCM that cruise
control is currently active. Upon receipt of this message the TCM selects a new transmission shift
map. This map has been developed to reduce busy gearshift during cruise mode. It has also been
developed to increase fuel economy.
Hot Mode
This is one of the adaptive modes the transmission can enter when conditions are correct. When the
transmission fluid temperature, chip temp, engine oil temp or coolant temperature becomes hot
enough to reach threshold values, the TCM will cause the transmission to enter Hot mode. This mode
will automatically engage new shift and lock-up maps to reduce heat generated within the
transmission. The shift map will enable the transmission to change to higher gears at lower vehicle
speeds and the lock-up map will engage the lock-up clutch at lower vehicle speeds and in lower
gears. The effect of this is that less heat will be generated within the transmission due to the effects
of lock-up clutch slip and churning effects. There will be forced upshift strategy used in hot mode. To
exit hot mode the selector lever must be moved or the brake pedal applied or the accelerator pedal
applied 100%, during all of these methods of exiting from hot mode the fluid temperature must be
lower than the threshold values.
Traction Control Mode
Traction Control Mode is an adaptive mode, which is automatically engaged when a traction event
occurs. When driving on slippery surfaces (i.e.sand, ice) it is possible for the driven wheels to begin to
spin. The TCM believes the vehicle speed is increasing and therefore it may begin to upshift. These
upshifts reduce the torque at the wheel and so tend to reduce wheel slip. The downshift lines are
forced downwards to prevent unwanted shifts. To reduce the effects of this, if a traction event
occurs a signal is transmitted by the ABS module to the TCM over the CAN network, the TCM uses
this signal to change the currently selected shift map. The new shift map will have gearshift lines
further apart, thus inhibiting the transmission shifting to a lower gear.
Hill/Trailer Towing Mode
This is an adaptive mode. When the TCM detects reduced vehicle acceleration for a certain
percentage of throttle opening then this mode is automatically engaged by the TCM. When this
mode is engaged a new shift map and torque converter lock-up map is selected. This new shift map is
designed to reduce the number of gearshifts when towing a trailer or with the car climbing a steep
hill. The shift map will cause the transmission to hold on to gears for longer this increases
acceleration and reduces the number of gearshifts. This mode can also give an advantage when
driving at high altitudes, where the torque produced by an engine is greatly reduced by the effects of
reduced ambient pressure and airflow.
Driving Mode Priority
Each of the above modes has an associated priority i.e. Normal mode cannot over-ride cruise mode
etc.
Adaptive Shift Strategies
The TCM of the six speed ZF automatic transmission incorporates adaptive strategies which improve
the accessibility of the vehicle`s performance in driving conditions while maintaining a relaxed driving
experience when cruising.
In "Sport" mode, accelerator pedal usage and cornering behaviour are monitored to assess driving
style and road conditions. When an enthusiastic driving style or a demanding road is detected, 6th
gear is inhibited and the lower gears are made slightly more accesssible in order to prevent
unwanted "hunting" between gears. Conversely, when cruising conditions are detected, 6th gear is
once again made available to maximise driving refinement and economy.
Under conditions of heavy braking, the transmission will perform one or more downshifts to improve
response to a subsequent accelerator pedal application. Similarly if the accelerator pedal is released
rapidly following hard acceleration, one or more upshifts are inhibited to increase engine braking and
also improve subsequent response.
To complement these features, when a corner is detected transmission upshifts are inhibited. This
inhibition is also maintained for a short distance after the corner allowing the driver to achieve a
smooth balance through the bend without unwanted shifting mid-corner.
Safety features
The safety functions are designed to safeguard against mis-operation by the driver as well as against
system malfunctions. The mis-operation system prevents reverse gear from being engaged at high
forward speeds (Above 5 kph) and prevents manual downshifting at excessive engine speeds.
Great attention has been paid to safeguarding against, and detecting, malfunctions in the electronic
control system. The design of the electrical and diagnostic system is such that system integrity is
protected at all times.
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The hydraulic system has "fail-safe" characteristics regarding its electrical energisation, i.e. as a result
of the power supply being lost to the electro-hydraulic actuators the transmission engages a reliable
emergency gear ratio to facilitate a basic limp-home mode.
Recognition of critical shift operation by monitoring the last element in the signal path, i.e. the
solenoid valve, and checking by means of redundant measured variables, i.e. engine speed, input
speed and output speed.
Measures are in place which guarantee a high degree of availability of safeguard functions, i.e.
monitoring of safety circuits. For this purpose each time the vehicle is started there is a check on the
entire safety hardware, this is during TCM initialization and the associated program parts and signal
paths used during the TCM operation status. A malfunction in this part of the system, or triggering of
the safety circuit, will be communicated to the driver by the instrument cluster message centre.
Diagnosis and testing
Diagnostic Strategy
No Data Available
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