1994 JAGUAR XJ6 four wheel drive

Automatic Transmission (AJ16)
Both types of automatic transmission comprise a hydrodynamic torque converter driving an epicyclic gear train which
provides four forward ratios and reverse. Gearshift selection is made by a hydraulic (or electronichydraulic) trans- mission control unit. Six gearshift positions are provided:
Position
'P' (Park) -the driven wheels are mechanically locked at the transmission.
Position
'R' (Reverse) - reverse gear selected.
Position
'N' (Neutral) - engine disconnected from drive-line and wheels.
Position 'D' (Drive)
- all four speed ranges are selected automatically with lock-up available in top gear only.
Position
'3' - automatic selection of the lowest three speed ranges only.
Position '2'
- automatic selection of the lowest two speed ranges only; the transmission is prevented from shift- ing up to the third and top speed ranges.
Immediate selection of a lower ratio is also available, within mapped limits, by 'kick
-down' (pressing the accelerator
pedal down beyond the normal full throttle position) for example when overtaking.
A brake pedal/gearshift interlock is incorporated in the shift lever mechanism. Theshift lever may only be movedfrom
the 'P' (Park) position if the ignition key switch is in position 'll', 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. The gearshift interlock may be over-ridden manually in the event
of an electrical failure or when it is required to move the vehicle manually for access, ie for removal of the propeller
shaft.
8.1.1.1
Gearshift selection causes the appropriate gear to be selected through a cable operated shift lever on the side of the
Gear Selection (ZF 4HP 22)
transmission unit. When a gea; is selected, the shift points are determined by accelerator pedal position through a
throttle cable connection and by pressures equivalent to road speed derived from a centrifugal governor on the output
shaft.
Gearshift speed and quality are controlled by the hydraulic control unit located in the lower part of the transmission
housing. The control unit contains selector valve, control pistons and pressure valves.
The hydraulic control unit can be overridden by 'kickdown'. This is actuated by the final travel of the accelerator pedal
and causes the next lower gear to be selected.
8.1.1.2
Gearshift selection causes the appropriate gear to be selected through a cable operated shift lever on the side of the
transmission unit; the shift lever also operates a rotary switch attached to the side of the transmission unit. When a
gear is selected, the rotary switch provides an output or combination of outputs to the TCM, which continuously moni
- tors the gear selected in addition to output shaft speed and transmission oil temperature. Information from the Engine
Control Module (ECM) representing engine speed, load and throttle position is also fed to the TCM to enable the most
suitable gear to be selected.
Gear selection and gearshift speeds are controlled by the manually operated selector valve, a solenoid operated pres
- sure regulator and three solenoid valves. On receipt of signalsfrom the TCM, the three solenoid valves MVI, MV2 and
MV3, in various combinations with the safety valve, determine the appropriate gear range. The TCM, on receipt of
information of engine state and road speed, determines the shift speed.
The Performance Mode switch, located on the shift lever surround, provides two alternative shift speed patterns:
1. 'Normal (Economy) Mode' - designed for everyday use.
2. 'Sport Mode'
- gear shift takes place at higher road speeds to enhance performance.
The 'kick
-down' switch, located beneath the accelerator pedal, is actuated by the final travel of the pedal and signals
to the TCM that the next lower gear is to be selected.
Gear Selection (ZF 4 HP 24 E)
X300 VSM 3 Issue 1 August 1994

12.1 ANTI-LOCK BRAKING SYSTEM (ASS), GENERAL DESCRIPTION
The anti-lock braking system (ABS) components are combined with a hydraulic booster and tandem master cylinder (TMC) to provide a two-circuit braking system. The anti-lock braking system comprises the following components:
0 Four inductive wheel speed sensors, hub end mounted
0 ABS warning light
0 Hydraulic module.
The hydraulic module consists of an electric motor driven pump,
two low pressure accumulators, valve block and an
ABS electronic control module.
m: Electronic control modules for vehicles without traction control are designated ABS CM. Control modules for
vehicles with traction control are designated ABS /TC CM.
The valve block houses solenoid operated valves which are activated by voltage signals from the control module. The
signals are generated using wheel speed information received from the wheel speed sensors.
For vehicles without traction control the valves operate on three circuits, two front and one rear, as necessary to pre
- vent wheel locking during braking. Brake pressure is modulated individually at thefront wheels and collectively at the
rear. Rear wheel control operates on a 'select low' principle i.e. locking in either wheel is sensed, and controlled brake
pressure is applied to both wheels.
For vehicles with traction control the valves operate on four circuits. During ABS control the rear wheel are controlled
on a 'select low' principle (as above), but during traction control operation the rear wheels are controlled individually.
0
1yQfB: Functional and diagnostic information for the ABS CM and the ABS/TC CM is contained in the Electrical Diag-
nostic Manual (EDM), Section 12.
ABS Warning lamp / Traction Control Warning lamp /Fluid level Indicator
The ABS and traction control warning lamps, mounted in the instrument panel, indicate a fault in the ABS or traction
control. These systems are inhibited or disabled when the lamps are lit, although conventional braking is unaffected.
When the ignition is switched on, an ABS self test is initiated. During this test, the ABS and traction control warning
lamps are
lit for approximately 1.7 seconds and then extinguish. A fault is indicated if the warning lamps remain lit or
come on whilst the vehicle is being driven.
W: The ABS self test is masked by the 5 second lamp test initiated when the ignition is switched on.
The fluid level indicator lamp, mounted in the instrument panel, is
lit when the brake fluid falls below the minimum
mark on the brake fluid reservoir.
ABS / Traction Control - Inhibit / Disable
Faults conditions are detected by the ABS/TC CM which disables the ABS and traction control until the fault is rectified.
The ABS and traction control warning lights on the instrument pack remains lit whilst a fault exists. The system will
be disabled when the following conditions occur:
0
0 Valve failure
0 Sensor failure
0 Main driver failure (internal ABS /TC CM fault)
0 Redundancy error (internal ABS JTC CM fault)
0 Overvoltage J undervoltage
0 Pump motor failure.
0 Throttle valve actuator motor failure (traction control vehicles only).
0 Throttle valve actuator potentiometer failure (traction control warning light only).
X300 VSM 1 Issue 1 August 1994

12.1.5. ABS Components
Hydraulic Module
The hydraulic module is located under the bonnet adjacent
to the engine compartment firewall. It is secured within a steel mounting bracket at three securing points. All elec- tronic and power connections are made through one cable
loom connect ion.
The hydraulic pump
(1 Fig. 1) is a reciprocating two-circuit pump in which one brake circuit is assigned to each pump
circuit. The pump supplies adequate pressure and volume
supply to the brake circuits under anti
-lock braking condi- tions. The pump is driven by and electric motor (2 Fig. 1). The
pump housing incorporates two low pressure accumulators
and damping chambers for each brake circuit.
A modulator valve block
(3 Fig. 1) incorporates the ABS CM or ABS / TC CM (4 Fig. 1). Vehicles with traction control are
fitted with a throttle position actuator (5 Fig. I), which is an
electrical device controlled by the ABS 1 TC CM.
Valve blocks on vehicles without traction control comprise
six solenoid valves, three normally open (NO) inlet valves
and three normally closed
(NC) outlet valves. These valve
blocks have three outlet ports. Valve blocks on vehicles with
traction control comprise nine solenoid valves, four
NO inlet valves,four NC outlet valves and one special isolating valve.
Fig. 2 shows a hydraulic module for vehicles with traction
control. The valve block (2 Fig. 2) has four outlet ports (Indi- vidual control of the driven wheels).
A BS CM, A BS / TC CM
The ABS CM or ABS TCI CM locates beneath the modulator
valve block and is secured by
two screws. The CM houses
the solenoids which operate the inlet and outletvalves of the
modulator valve block. When fitted, the valve stems locate
in the
CM mounted solenoids. There is no electrical connec- tion between the CM and the modulator valve block. Fig. 3 shows an ABS TC 1 CM having nine solenoids.
The
CM functions include the following:
0 Providing control signals for the operation of ABS
and traction control solenoid valves
0 Calculating wheel speed from voltage signals trans- mitted by the wheel speed sensors
0 Monitoring of all electrical components
0 On Board Diagnostics (OBD): storage of possible fail- ures in a non-volatile memory.
The signals from the four wheel speed sensors are indepen
- dently processed by the ABS CM or ABSITC CM, calculating
numerical values which correspond directly to the wheel
speed. These values are converted into control signals for
pressure modulation during ABS control.
The ABS and traction control
are continuously monitored,
whilst the ignition is on,for possiblefaults and interruptions.
If a fault is detected, the module deactivates the ABS and
indicates this by lighting the ABS warning lamp. In a fault
condition, conventional braking is unaffected. The module
stores fault codes in a non
-volatile memory which can be
read via the OBD link.
U: For electrical diagnostic information on the ABS I traction control systems, refer to EDM, Section 12. Fia.
1
Fia. 2
Fin. 3 I
J70286
Issue 1 August 1994 X300 VSM