1994 JAGUAR XJ ignition

1.1.6 Gearshift Selection
Gearshift selection is by movement of the shift lever which through a selector cable causes repositioning ofthe manual
(selector) valve to direct oil pressure to the required shift valve. The automatic shift points are determined by acceler- ator position and road speed: throttle movement moves a cam on the throttle valve, directing oil pressure to the shift
valves and modulator valve, road speed modulates hydraulic pressure through a centrifugal governor driven by the
transmission output shaft. Operation
of the hydraulic control system is shown diagrammatically in the circuit dia
-
grams on the following pages.
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1. Engine 8. Pump regulator valve 2. Torque converter 9. Damper
3. Pump 10. Governor valve 4. Clutch & gears 11. Shift valve 5. Governor 12. Kickdown cable &throttle cam 6. Shift 13. Throttle / modulator valves 7. Solenoid valve 14. Transmission housing
Fig.
1 Schematic Diagram of Hydraulic Control
I. 1.7 Throttle Valve Mechanism (kick-down)
The throttlevalve or 'kick-down' mechanism comprises a cable connected between throttle body pedal and the throttle
valve cam/ quadrant located on the selector valve shaft; the cam operates the throttle valve housed within the throttle
valve block. The travel of the valve is proportional to throttle positions and alters shift speeds and pressures during
gearshifts to take account of throttle position. The mechanism also provides for immediate selection of a lower
ratio (eg when overtaking) by depressing the accelerator beyond the normal full
-throttle position. 'Kick-down' is oper- ated by movement of the throttle cable into the 'kick-down' position causing full movement of the throttle valve and
directing oil flow to the shift valves.
1.1.8 Starter Inhibit Switch
The starter inhibit switch prevents the starter motor from being operated when the shift lever is not in position 'P' - Park or position 'N'- Neutral. The switch is located in the gear selector housing.
I. I. 9 Gearshift Interlock
A brake pedal /shift lever interlock is incorporated in the gearselector mechanism. Theshift lever may only be moved
from the 'P'- Park position if the ignition key switch is in position '11', and the foot brake pedal is applied. The ignition
key cannot be removed from the ignition switch unless the shift lever is in the 'P' -Park position. Once the ignition key
has been removed, the shift lever is locked in the park position.
The gearshift interlock is operated by an electrical solenoid located adjacent to the selector; an override latch is incorpo
- rated into the mechanism to enable the gearshift interlock to be manually overridden in the event of electrical failure
or when towing.
8 Issue 1 August 1994

ZF Automatic Transmissions Service Manual
2.1.6 Transmission Rotary Switch
This switch is located on a square extension of the transmission selector shaft and is linked to the shift lever via the
selector cable. The switch comprises a selector bar which moves across a series of copper segments located on the
switch quadrant. The copper segments are set out in seven bands, each band providing an electrical output or com
- bination of outputs to the TCM.
The electrical outputs to the TCM are in the form of a three
-digit code which takes up three of the seven bands of the
quadrant; the remaining four bands are used for reverse, ground and start inhibit.
2.1.7 Decoder Module
The decoder module, located on the right hand side of the J-gate assembly, is used to translate the three-digit codes
from the rotary transmission switch into single-line functions to feed the illumination module and to provide the fol-
lowing information:
. Cruise control, ie when cruise control can or cannot be engaged.
. Indication when the vehicle is not in 'P' Park.
. Provide the ECM with a Park/ Neutral signal.
2.1.8 Performance Mode Switch
This switch, located on the shift lever surround, provides two alternative shift patterns:
. 'Normal Mode' -for everyday use,
. 'Sport Mode'- gear changes take place at higher road speeds in order to enhance performance.
Note: Torque converter 'lock-up' occurs in fourth gear in each mode.
2. I. 9 'Kick-down' Mechanism
'Kick-down' is activated by the final travel of the accelerator pedal which contacts a floor-mounted switch located be- hind the pedal. Operation of the switch provides a signal to the TCM that a downward change is required. The switch
is adjustable to ensure that the pedal does not overtravel and stretch the cable.
2.1.10 Reverse Safefy Inhibit
If 'R' Reverse is selected when the vehicle is travelling forwards at more than 5 mile / h, solenoid valve MV2 will be
energised to prevent engagement of reverse gear.
2.1.11 Gearshift hterlock
A brake pedal /gearshift interlock is incorporated in the gear selector mechanism. The gear selector lever may only
be moved from the P - Park position if the ignition key switch is in position II and the foot brake is applied.
The ignition key cannot be removed from the ignition switch unless the shift lever is in
the 'P - Park position. Once
the ignition key has been removed, the shift lever is locked in the park position.
2.1.12 Starter Inhibit Switch
The starter inhibit switch prevents the starter motor from being operated when the shift lever is not in position 'P' - Park or position 'N' - Neutral. The switch is located in the gear selector housing.
issue 1 August 1994 47

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AFLR M- -1
4 13 9
14
15 7
J44-718
1.
Selector 2. Mode switch 3. Rotary switch
4. Transmission control unit 5. Output shaft speed sensor 6. Kick-down switch 7. Battery
8. Transmission relay
9.
10.
11.
12.
13.
14.
15.
16.
Transmission control module (TCM)
Reverse lamps
Start inhibiter
Engine speed
Ignition retard
Engine load
Engine control module
(ECM) Engine speed sensor
Fig.
1 Control Layout Schematic
2.1.5 Transmission Control Module (TCM)
The Transmission Control Module (TCM) is an electronic control unit located in the front passenger footwell behind
the underscuttle pad. It is electrically connected to the transmission and other components through a cable harness
and multiple pin plug.
The TCM continuously monitors the gear selected (via the rotary transmission switch), the speed of the output shaft
(by speed sensor on the output shaft) and throttle position ('kick
-down' switch). This information plus input from the
Engine Control Module (ECM) of throttle angle and engine speed and load in conjunction with a pre-programmed con- trol map, enables the most suitable gear to be selected.
The TCM, by operating solenoid valves
MVI, MV2 and MV3, controls the gear shift speed and in conjunction with the
solenoid operated pressure control valve, controls the gear shift quality. Gear shift quality on upshifts is improved by
the TCM momentarily retarding the ignition to reduce the torque input as the gear change takes place. Information
is fed to the TCM from sensors and
if any electronic component fails, the basic shift changes will be performed by the
hydro-mechanical system, ie Park, Reverse, Neutral, D3 or D4.
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Issue 1 August 1994