1997 JAGUAR XJ6 stop start

3261 Jaguar XJ6
Weekly checks0•13
Power steering
fluid level
Before you start:
4Park the vehicle on level ground.
4Set the steering wheel straight-ahead.
4The engine should be turned off.
Safety first!
lThe need for frequent topping-up indicates
a leak, which should be investigated
immediately.
For the check to be
accurate, the steering must
not be turned once the
engine has been stopped.
Wipe clean the area around the reservoir
cap then remove the cap noting that it
unscrews in a clockwise direction (see
arrow on cap).1Wipe clean the cap dipstick then insert it
fully into the reservoir and withdraw it.2
Note the fluid level on the end of the
dipstick. If the fluid is cold (vehicle not
having been used) the fluid level should
be upto the COLD level marking (1). If the
vehicle has been driven and the fluid is hot
then the fluid level should be upto the upper
(HOT) level marking (2).3If necessary, top-up the reservoir with the
specified type of fluid (note that the type
of fluid differs according to model - see
“Lubricants, fluids and tyre pressures” on
page 0•16). Once the level is correct, securely
refit the reservoir cap. Do not overfill the
reservoir.4
Wiper blades
Check the condition of the wiper blades:
if they are cracked or show signs of
deterioration, or if the glass swept area is
smeared, renew them. For maximum clarity of
vision, wiper blades should be renewed
annually.1To remove a wiper blade, pull the arm
fully away from the screen until it locks.
Swivel the blade then depress the locking
clip at the base of the mounting block and
slide the blade off the arm.2
Warning:
l This check applies only to
vehicles fitted with a separate
power steering system. For
vehicles fitted with power
steering where the fluid
reservoir is part of the power hydraulic
system, this weekly check is not
applicable.
l It is essential to use the correct power
steering fluid, this being dependent on the
year of manufacture and type of system
fitted. A label attached to the fluid
reservoir will indicate the specification of
fluid. However, if necessary refer to the
driver’s handbook supplied with the
vehicle or to your local Jaguar dealer.

3261 Jaguar XJ6
Weekly checks0•15
Battery
Caution:Before carrying out any work on the
vehicle battery, read the precautions given in
"Safety first" at the start of this manual.
4Make sure that the battery tray is in good
condition, and that the clamp is tight.
Corrosion on the tray, retaining clamp and the
battery itself can be removed with a solution
of water and baking soda. Thoroughly rinse all
cleaned areas with water. Any metal parts
damaged by corrosion should be covered
with a zinc-based primer, then painted.
4Periodically (approximately every three
months), check the charge condition of the
battery as described in Chapter 5.
4If the battery is flat, and you need to jump
start your vehicle, see Roadside Repairs.
The battery is located in the left-hand,
rear corner of the engine compartment.
Check the battery terminals for signs of
corrosion and examine the battery leads
closely for signs of damage.1Check the battery lead clamps for
tightness to ensure good electrical
connections.2
Battery corrosion can be kept to a
minimum by applying a layer of
petroleum jelly to the clamps and
terminals after they are reconnected.If corrosion (white, fluffy deposits) is
evident, remove the cables from the
battery terminals, clean them with a small
wire brush, then refit them. Automotive stores
sell a tool for cleaning the battery post . . .3. . . as well as the battery cable clamps4
Bulbs and fuses
4Check all external lights and the horn. Refer
to the appropriate Sections of Chapter 12 for
details if any of the circuits are found to be
inoperative.4Visually check all accessible wiring
connectors, harnesses and retaining clips for
security, and for signs of chafing or damage.
If you need to check your
brake lights and indicators
unaided, back up to a wall or
garage door and operate the
lights. The reflected light should show if
they are working properly.
If a single indicator light, stop light or
headlight has failed, it is likely that a bulb
has blown and will need to be replaced.
Refer to Chapter 12 for details. If both stop
lights have failed, it is possible that the switch
has failed (see Chapter 9).If more than one indicator light or tail light
has failed it is likely that either a fuse has
blown or that there is a fault in the circuit.
The fuseboxes are located behind the left and
right side kick panels and in the centre
console glove box (see Chapter 12).
2
To replace a blown fuse, simply pull it out
and fit a new fuse of the correct rating
(see Chapter 12). If the fuse blows again,
it is important that you find out why - a
complete checking procedure is given in
Chapter 12.31

exhaust components will be warm during the
actual work, so try to anticipate any potential
problems before the engine and accessories
are hot.
5Park the vehicle on a level spot. Start the
engine and allow it to reach its normal
operating temperature (the needle on the
temperature gauge should be at least above
the bottom mark). Warm oil and contaminates
will flow out more easily. Turn off the engine
when it’s warmed up. Remove the oil filler cap
located next to the valve cover.
6Raise the vehicle and support it on axle
stands.
Warning: To avoid personal
injury, never get beneath the
vehicle when it is supported by
only by a jack. The jack provided
with your vehicle is designed solely for
raising the vehicle to remove and replace
the wheels. Always use axle stands to
support the vehicle when it becomes
necessary to place your body underneath
the vehicle.
7Being careful not to touch the hot exhaust
components, place the drain pan under the
drain plug in the bottom of the pan and
remove the plug (see illustration). You may
want to wear gloves while unscrewing the
plug the final few turns if the engine is really
hot.
8Allow the old oil to drain into the pan. It may
be necessary to move the pan farther under
the engine as the oil flow slows to a trickle.
Inspect the old oil for the presence of metal
shavings and chips.
9After all the oil has drained, wipe off the
drain plug with a clean rag. Even minute metal
particles clinging to the plug would
immediately contaminate the new oil.
10Clean the area around the drain plug
opening, refit the plug and tighten it securely,
but do not strip the threads.
11Move the drain pan into position under the
oil filter.
12Remove all tools, rags, etc. from under
the vehicle, being careful not to spill the oil in
the drain pan, then lower the vehicle.
13Loosen the oil filter (see illustration)by
turning it anti-clockwise with the filter wrench.
Any standard filter wrench should work. Oncethe filter is loose, use your hands to unscrew
it from the block. Just as the filter comes
away from the block, immediately tilt the open
end up to prevent the oil inside the filter from
spilling out.
Warning: The engine exhaust
pipes may still be hot, so be
careful.
14With a clean rag, wipe off the mounting
surface on the block. If a residue of old oil is
allowed to remain, it will smoke when the
block is heated up. It will also prevent the new
filter from seating properly. Also make sure
that the none of the old gasket remains stuck
to the mounting surface. It can be removed
with a scraper if necessary.
15Compare the old filter with the new one to
make sure they are the same type. Smear
some engine oil on the rubber gasket of the
new filter and screw it into place (see
illustration). Because over-tightening the
filter will damage the gasket, do not use
a filter wrench to tighten the filter. Tighten it by
hand until the gasket contacts the seating
surface. Then seat the filter by giving it an
additional 3/4-turn.
16Add new oil to the engine through the oil
filler cap next to the valve cover. Use a spout
or funnel to prevent oil from spilling onto the
top of the engine. Pour three litres of fresh oil
into the engine. Wait a few minutes to allow
the oil to drain into the pan, then check the
level on the oil dipstick (see “Weekly checks”).
If the oil level is at or near the H mark, refit the
filler cap hand tight, start the engine and allow
the new oil to circulate.
17Allow the engine to run for about a minute.
While the engine is running, look under the
vehicle and check for leaks at the sump drain
plug and around the oil filter. If either isleaking, stop the engine and tighten the plug
or filter slightly.
18Wait a few minutes to allow the oil to
trickle down into the pan, then recheck the
level on the dipstick and, if necessary, add
enough oil to bring the level to the H mark.
19During the first few trips after an oil
change, make it a point to check frequently
for leaks and proper oil level.
20The old oil drained from the engine cannot
be reused in its present state and should be
disposed of. Check with your local authority,
or with a local garage to see whether they will
accept the oil for recycling. Don’tpour used
oil into drains or onto the ground. After the oil
has cooled, it can be drained into a suitable
container (capped plastic jugs, topped
bottles, etc.) for transport to an approved
disposal site.
4 Spark plug check
2
1Spark plug renewal requires a spark plug
socket which fits onto a ratchet spanner. This
socket is lined with a rubber grommet to
protect the porcelain insulator of the spark
plug and to hold the plug while you insert it
into the spark plug hole. You will also need a
wire-type feeler gauge to check and adjust
the spark plug gap and a torque wrench to
tighten the new plugs to the specified torque
(see illustration).
2If you are replacing the plugs, purchase the
new plugs, adjust them to the proper gap and
then replace each plug one at a time. Note:
When buying new spark plugs, it’s essential
that you obtain the correct plugs for your
specific vehicle. This information can be found
in the Specifications Section at the beginning
of this Chapter, on the Vehicle Emissions
Control Information (VECI) label located on the
underside of the bonnet (where fitted)or in the
owner’s manual. If these sources specify
different plugs, purchase the spark plug type
specified on the VECI label because that
information is provided specifically for your
engine.
Every 7500 miles or 6 months 1•7
1
3.7 The oil drain plug (arrowed) is located
at the rear of the sump - use a ring
spanner or socket to remove it3.13 The oil filter is located on the left side
of the engine - use a filter wrench for
removal (tighten the new filter by hand)3.15 Lubricate the oil filter gasket with
clean engine oil before refitting the filter
3261 Jaguar XJ6
Note: It is
antisocial and
illegal to dump oil
down the drain.
To find the
location of your
local oil recycling
bank, call this
number free.

silencer and catalytic converter. If the
components can come in contact with the
body or suspension parts, secure the exhaust
system with new mounts.
5Check the running condition of the engine
by inspecting inside the end of the tailpipe.
The exhaust deposits here are an indication of
engine state-of-tune. If the pipe is black and
sooty or coated with white deposits, the
engine is in need of a tune-up, including a
thorough fuel system inspection.
11 Braking system - general
check and adjustment
2
Warning: The dust created by
the brake system may contain
asbestos, which is harmful to
your health. Never blow it out
with compressed air and don’t inhale any
of it. An approved filtering mask should be
worn when working on the brakes. Do not,
under any circumstances, use petroleum-
based solvents to clean brake parts. Use
brake system cleaner only! Try to use non-
asbestos replacement parts whenever
possible.
Note: For detailed photographs of the brake
system, refer to Chapter 9.
1In addition to the specified intervals, the
brakes should be inspected every time the
wheels are removed or whenever a defect is
suspected. Any of the following symptoms
could indicate a potential brake system
defect: The vehicle pulls to one side when the
brake pedal is depressed; the brakes make
squealing or dragging noises when applied;
brake pedal travel is excessive; the pedal
pulsates; brake fluid leaks, usually onto the
inside of the tyre or wheel.
2The disc brakes have built-in electrical wear
indicators which cause a warning lamp to
illuminate on the instrument panel when
they’re worn to the renewal point. When the
warning light comes on, replace the pads
immediately or expensive damage to the
discs can result.
3Loosen the wheel nuts.
4Raise the vehicle and place it securely on
axle stands.
5Remove the wheels.
Disc brakes
6There are two pads (an outer and an inner)
in each caliper. The pads are visible through
inspection holes in each caliper (see Haynes
Hint).
7Check the pad thickness by looking at each
end of the caliper and through the inspection
hole in the caliper body. If the lining material is
less than the thickness listed in this Chapter’s
Specifications, replace the pads. Note:Keep
in mind that the lining material is riveted or
bonded to a metal backing plate and the metal
portion is not included in this measurement.8If it is difficult to determine the exact
thickness of the remaining pad material by the
above method, or if you are at all concerned
about the condition of the pads, remove the
caliper(s), then remove the pads from the
calipers for further inspection (see Chapter 9).
9Once the pads are removed from the
calipers, clean them with brake cleaner and
re-measure them with a ruler or a vernier
caliper.
10Measure the disc thickness with a
micrometer to make sure that it still has
service life remaining. If any disc is thinner
than the specified minimum thickness,
replace it (refer to Chapter 9). Even if the disc
has service life remaining, check its condition.
Look for scoring, gouging and burned spots. If
these conditions exist, remove the disc and
have it resurfaced (see Chapter 9).
11Before refitting the wheels, check all
brake lines and hoses for damage, wear,
deformation, cracks, corrosion, leakage,
bends and twists, particularly in the vicinity of
the rubber hoses at the calipers (see
illustration). Check the clamps for tightness
and the connections for leakage. Make sure
that all hoses and lines are clear of sharp
edges, moving parts and the exhaust system.
If any of the above conditions are noted,
repair, reroute or replace the lines and/or
fittings as necessary (see Chapter 9).
Hydraulic brake servo check
12Sit in the driver’s seat and perform the
following sequence of tests.
13Start the engine, run it for about a minute
and turn it off. Then firmly depress the brake
several times - the pedal travel should
decrease with each application.
14With the brake fully depressed, start the
engine - the pedal should move down a little
when the engine starts.
15Depress the brake, stop the engine and
hold the pedal in for about 30 seconds - the
pedal should neither sink nor rise.
16If your brakes do not operate as
described above when the preceding tests
are performed, the brake servo is either in
need of repair or has failed. Refer to Chapter 9
for the removal procedure.
Handbrake
17Slowly pull up on the handbrake and
count the number of clicks you hear until the
handle is up as far as it will go. The
adjustment should be within the specified
number of clicks listed in this Chapter’s
Specifications. If you hear more or fewer
clicks, it’s time to adjust the handbrake (refer
to Chapter 9).
18An alternative method of checking the
handbrake is to park the vehicle on a steep hill
with the handbrake set and the transmission
in Neutral (be sure to stay in the vehicle during
this check!). If the handbrake cannot prevent
the vehicle from rolling, it is in need of
adjustment (see Chapter 9). Whenever a fault
is suspected, the brake discs should be
removed and the handbrake assemblies
themselves should be visually inspected.
12 Steering
and suspension check
2
Note: The steering linkage and suspension
components should be checked periodically.
Worn or damaged suspension and steering
linkage components can result in excessive
and abnormal tyre wear, poor ride quality and
vehicle handling and reduced fuel economy.
For detailed illustrations of the steering and
suspension components, refer to Chapter 10.
With the wheels on the ground
1Park the vehicle on level ground, turn the
engine off and set the handbrake. Check the
tyre pressures and check that the wheel nuts
are tightened to the specified torque.
2Push down at one corner of the vehicle,
then release it while noting the movement of
the body. It should stop moving and come to
rest in a level position with one or two
bounces. When bouncing the vehicle up and
down, listen for squeaks and noises from the
suspension components.
3If the vehicle continues to move up-and-
down or if it fails to return to its original
1•12Every 7500 miles or 6 months
11.11 Check along the brake hoses
and at each fitting (arrowed) for
deterioration and cracks
3261 Jaguar XJ6
You will find an inspection hole like this
in each caliper - placing a ruler across
the hole should enable you to determine
the thickness of remaining pad material
for both inner and outer pads

5After the coolant stops flowing out of the
radiator, move the container under the engine
block drain plug. Remove the plug and let the
coolant in the block to drain (see illustration).
6While the coolant is draining from the
engine block, check the condition of the
radiator hoses, heater hoses and clamps
(refer to Section 7 if necessary).
7Replace any damaged clamps or hoses
(see Chapter 3).
Flushing
8Once the system is completely drained,
flush the radiator with fresh water from agarden hose until water runs clear at the drain.
The flushing action of the water will remove
sediments from the radiator but will not
remove more serious rust and scale from the
engine and cooling tube surfaces.
9These deposits can be removed by using
proprietary chemical cleaners. It should be
stressed, however, that these should only
need to be used if the system has been
neglected. Follow the procedure outlined in
their manufacturer’s instructions. If the
radiator is severely corroded, damaged or
leaking, it should be removed (see Chapter 3)
and taken to a radiator repair workshop.10On 1988 and 1989 models remove the
overflow hose from the coolant recovery
reservoir. Drain the reservoir and flush it with
clean water, then reconnect the hose (see
Chapter 3).
Refilling
11Close and tighten the radiator drain. Refit
and tighten the engine block drain plugs.
12Make sure the heater temperature control
is in the maximum heat position.
13Slowly refill the expansion tank with a
mixture of antifreeze and water until the
coolant reaches the base of the filler neck.
14Leave the expansion tank pressure cap
off and run the engine in a well-ventilated area
until the thermostat opens (coolant will begin
flowing through the radiator and the upper
radiator hose will become hot). Race the
engine two or three times under no load.
15Turn the engine off and let it cool. Add
more coolant mixture to bring the level back
up to the base of the filler neck.
16Squeeze the upper radiator hose to expel
air, then add more coolant mixture if
necessary. Refit the expansion tank pressure
cap.
17Start the engine, allow it to reach normal
operating temperature and check for leaks.
Every 2 years 1•21
1
3261 Jaguar XJ6
30.4 The radiator drain fitting (arrowed)
located at the bottom of the radiator30.5 The block drain plug (arrowed) is
located on the right side of the block

connecting rods. Apply a light coat of oil to
the bolt threads and the under sides of the
bolt heads, then refit them. Tighten all main
bearing cap bolts to the torque listed in this
Chapter’s Specifications, starting in the centre
and working out to the ends.
21Rotate the crankshaft a number of times
by hand to check for any obvious binding.
22Check the crankshaft endplay with a
feeler gauge or a dial indicator as described in
Section 14. The endplay should be correct if
the crankshaft thrust faces aren’t worn or
damaged and new thrust washers have been
installed. Note:If the end-play is too great,
even with the new thrust bearings, oversized
thrust bearings are available. There are two
sizes, 0.005-inch and 0.010-inch oversize.
23Refit a new rear main oil seal, then bolt the
retainer to the engine block (see Section 24).
24 Rear main oil seal refitting
2
1The crankshaft must be installed first and
the main bearing caps bolted in place, then
the new seal should be installed in the retainer
and the retainer bolted to the engine block.
2Check the seal contact surface on the
crankshaft very carefully for scratches and
nicks that could damage the new seal lip and
cause oil leaks. If the crankshaft is damaged,
the only alternative is a new or different
crankshaft.
3Refer to Part A of this Chapter for refitting
of the new rear seal, using the plastic
alignment tool supplied with the engine
overhaul gasket set.
25 Pistons/connecting rods-
refitting and big-end bearing
oil clearance check
3
1Before refitting the piston/connecting rod
assemblies, the cylinder walls must be
perfectly clean, the top edge of each cylinder
must be chamfered, and the crankshaft must
be in place.
2Remove the cap from the end of the
number one connecting rod (refer to the
marks made during removal). Remove the
original bearing inserts and wipe the bearing
surfaces of the connecting rod and cap with a
clean, lint-free cloth. They must be kept
spotlessly clean.
Big-end bearing
oil clearance check
3Clean the back side of the new upper
bearing insert, then lay it in place in the
connecting rod. Make sure the tab on the
bearing fits into the recess in the rod so the oil
holes line up. Don’t hammer the bearing insert
into place and be very careful not to nick or
gouge the bearing face. Don’t lubricate the
bearing at this time.4Clean the back side of the other bearing
insert and refit it in the rod cap. Again, make
sure the tab on the bearing fits into the recess
in the cap, and don’t apply any lubricant. It’s
critically important that the mating surfaces of
the bearing and connecting rod are perfectly
clean and oil free when they’re assembled.
5Position the piston ring gaps at staggered
intervals around the piston (see illustration).
6Slip a section of plastic or rubber hose over
each connecting rod cap bolt.
7Lubricate the piston and rings with clean
engine oil and attach a piston ring compressor
to the piston. Leave the skirt protruding about
1/4-inch to guide the piston into the cylinder.
The rings must be compressed until they’re
flush with the piston.
8Rotate the crankshaft until the number one
connecting rod journal is at BDC (bottom
dead centre) and apply a coat of engine oil to
the cylinder wall.
9With the word FRONT (or the arrow) on top
of the piston facing the front of the engine
(see illustration), gently insert the piston/
connecting rod assembly into the number one
cylinder bore and rest the bottom edge of the
ring compressor on the engine block.
10Tap the top edge of the ring compressor
to make sure it’s contacting the engine block
around its entire circumference.11Gently tap on the top of the piston with
the end of a wooden hammer handle (see
illustration) while guiding the end of the
connecting rod into place on the crankshaft
journal. The piston rings may try to pop out of
the ring compressor just before entering the
cylinder bore, so keep some downward
pressure on the ring compressor. Work
slowly, and if any resistance is felt as the
piston enters the cylinder, stop immediately.
Find out what’s hanging up and fix it before
proceeding.
Caution: Do not, for any reason, force the
piston into the cylinder - you might break a
ring and/or the piston.
12Once the piston/connecting rod assembly
is installed, the big-end bearing oil clearance
must be checked before the rod cap is
permanently bolted in place.
13Cut a piece of the appropriate size
Plastigauge slightly shorter than the width of
the big-end bearing and lay it in place on the
number one connecting rod journal, parallel
with the journal axis (see illustration).
14Clean the connecting rod cap bearing
face, remove the protective hoses from the
connecting rod bolts and refit the rod cap.
Make sure the mating mark on the cap is on
the same side as the mark on the connecting
rod. Check the cap to make sure the front
mark is facing the timing chain of the engine.
15Apply a light coat of oil to the under sides
of the nuts, then refit and tighten them to the
torque listed in this Chapter’s Specifications,
Engine removal and overhaul procedures 2B•17
2B
25.13 Lay the Plastigauge strips on each
big-end bearing journal, parallel to the
crankshaft centreline
3261 Jaguar XJ6
25.5 Stagger the ring end gaps around the
piston as shown25.9 Pistons must be installed with the
arrow (right arrow) or FRONT facing the
front of the engine - left arrow indicates
piston size letter
25.11 The piston can be driven (gently)
into the cylinder bore with the end of a
wooden or plastic hammer handle
A Oil ring rail gaps
B Second compression ring gap
C Oil ring spacer gap
D Top compression ring gap

5Remove the air cleaner (see Chapter 1) and
the air cleaner housing (see Section 9).
6Remove the air intake duct.
7Detach the electrical connector from the
MAF sensor (see illustration).
8Remove the clamp that retains the MAF
sensor to the air intake duct (see illustration)
and lift the MAF sensor assembly from the
engine compartment.
9Detach the throttle cable from the bellcrank
(see Section 10), then remove the bellcrank
assembly from the throttle body (see
illustration).
10Detach the kickdown cable from the
bellcrank and set the cable and brackets
aside (see Chapter 7).
11Clearly label, then detach, all vacuum and
coolant hoses from the throttle body.
12Disconnect the electrical connector from
the throttle potentiometer.
13Remove the four throttle body mounting
bolts and detach the throttle body from the
intake manifold.
14Using a soft brush and carburettor
cleaner, thoroughly clean the throttle body
casting, then blow out all passages with
compressed air.
Caution: Do not clean the throttle position
sensor with any solvents or sprays. Just
wipe it off with a clean, soft cloth.
15Refitting of the throttle body is the reverse
of removal.
16Be sure to tighten the throttle body
mounting bolts to the torque listed in this
Chapter’s Specifications.
Adjustment
17Remove the air intake duct to expose the
throttle body and butterfly valve.
18Make sure the throttle body is clean and
free of burrs, nicks or carbon build-up (see
illustration).
19Measure the clearance between the
butterfly valve (throttle plate) and the wall of
the throttle body (see illustration). It should
be 0.05 mm (0.002 inch). 20If the gap is incorrect, loosen the throttle
stop locknut (see illustration)and turn the
throttle stop screw until the correct clearance
is attained.
21Refit the air intake duct and surrounding
components.
Idle Speed Control (ISC) motor
Note:The minimum idle speed is pre-set at
the factory and should not require adjustment
under normal operating conditions; however ifthe throttle body has been replaced or you
suspect the minimum idle speed has been
tampered with (for example, if the idle speed
screw was removed from the throttle body)
have the vehicle checked by a dealer service
department or a qualified automotive repair
workshop.Check
22Start the engine and allow it to reach
normal operating temperature. Switch on the
Fuel and exhaust systems 4•11
4
13.9 Remove the bellcrank assembly bolts
(arrowed) and separate it from the
throttle body13.18 The area inside the throttle body
near the throttle plate suffers from sludge
build-up because the PCV hose vents
crankcase vapour into the intake duct
13.19 Measure clearance between the
butterfly valve and the throttle body
3261 Jaguar XJ6 13.7 Push up on the clip and remove the harness connector from
the MAF sensor
13.8 Remove the air intake duct clamp from the
MAF sensor housing
13.20 Adjust the butterfly angle by
loosening the locknut on the throttle stop
and turning the adjustment bolt

components identified. When servicing the
engine or emissions systems, the VECI label
in your particular vehicle should always be
checked for up-to-date information.
2 Electronic control system
and ECU
General description
Note: These models are susceptible to ECU
damage if water is allowed to build up in the
front cowl drain and overspill into the dash
area near the computer. Inspect and clear the
front cowl drain as a regular maintenance item
to keep the water draining properly. Remove
the duckbill-type rubber hose and inspect it
for clogging, collapsing or deterioration.
1The Lucas LH Engine Management system
controls the fuel injection system by means of
a microcomputer known as the Electronic
Control unit (ECU).
2The ECU receives signals from various
sensors which monitor changing engine
operating conditions such as intake air mass,
intake air temperature, coolant temperature,
engine rpm, acceleration/deceleration,
exhaust oxygen content, etc. These signals
are utilised by the ECU to determine the
correct injection duration.
3The system is analogous to the central
nervous system in the human body: The
sensors (nerve endings) constantly relay
signals to the ECU (brain), which processes
the data and, if necessary, sends out a
command to change the operating
parameters of the engine (body).
4Here’s a specific example of how one
portion of this system operates: An oxygen
sensor, located in the exhaust manifold,
constantly monitors the oxygen content of the
exhaust gas. If the percentage of oxygen in
the exhaust gas is incorrect, an electrical
signal is sent to the ECU. The ECU takes this
information, processes it and then sends a
command to the fuel injection system telling it
to change the air/fuel mixture. This happens in
a fraction of a second and it goes on
continuously when the engine is running. The
end result is an air/fuel mixture ratio which is
constantly maintained at a predetermined
ratio, regardless of driving conditions.
5In the event of a sensor malfunction, a
backup circuit will take over to provide
driveability until the problem is identified and
fixed.
Precautions
6Follow these steps:
a) Always disconnect the power by either
turning off the ignition switch or
disconnecting the battery terminals before
removing electrical connectors.
Warning: Later models are
equipped with airbags. To
prevent accidental deployment ofthe airbag, which could cause personal
injury, DO NOT work in the vicinity of the
steering column or instrument panel. The
manufacturer recommends that, on airbag
equipped models, the following procedure
should be left to a dealer service
department or other repair workshop
because of the special tools and techniques
required to disable the airbag system.
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
sure you have the correct activation code
before disconnecting the battery.
b) When refitting a battery, be particularly
careful to avoid reversing the positive and
negative battery cables. Also, make sure
the ignition key is in the Off position when
connecting or disconnecting the battery.
c) Do not subject EFI components,
emissions-related components or the
ECU to severe impact during removal or
refitting.
d) Do not be careless during fault diagnosis.
Even slight terminal contact can invalidate
a testing procedure and damage one of
the numerous transistor circuits.
e) Never attempt to work on the ECU or
open the ECU cover. The ECU is
protected by a government-mandated
extended warranty that will be nullified if
you tamper with or damage the ECU.
f) If you are inspecting electronic control
system components during rainy weather,
make sure that water does not enter any
part. When washing the engine
compartment, do not spray these parts or
their electrical connectors with water.
g) These models are susceptible to ECU
damage if water is allowed to build up in
the front cowl drain and overspill into the
dash area. Inspect and clear the front
cowl drain system as a regular
maintenance item to keep the water
draining properly. Remove the duckbill
type rubber hose and inspect it for
clogging, collapsing or deterioration.
ECU removal and refitting
7Disconnect the negative cable from the
battery (see Chapter 5).
Warning: Later models are
equipped with airbags. To
prevent the accidental deploy-
ment of the airbag, which could
cause personal injury, DO NOT work in the
vicinity of the steering column or
instrument panel. The manufacturer
recommends that, on airbag equipped
models, the following procedure should be
left to a dealer service department or other
repair workshop because of the special
tools and techniques required to disable
the airbag system.
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
sure you have the correct activation code
before disconnecting the battery.8Remove the lower instrument panel on the
passenger side under the glove compartment
(see Chapter 11).
9Remove the glove compartment from the
passenger compartment (see Chapter 11).
10Remove the screws from the ECU bracket
(see illustration).
11Lower the ECU and unplug the electrical
connectors.
12Refitting is the reverse of removal.
3 On Board Diagnosis (OBD)
system- description and fault
code access
2
Note: 1990 and 1991 models may set
Code 69 erroneously. If the battery voltage
drops sufficiently and the ignition key is
switched quickly from OFF to START, battery
voltage will be lowered and during cranking
causing a delayed park/neutral signal from the
decoder module to the ECU. Check all the
battery connections and the condition of the
battery and then check the rotary switch
adjustment in Chapter 7 to remedy this code.
General information
1The ECU contains a built-in self-diagnosis
system which detects and identifies
malfunctions occurring in the network. When
the ECU detects a problem, three things
happen: the CHECK ENGINE light comes on,
the fault is identified and a diagnostic code is
recorded and stored. The ECU stores the
failure code assigned to the specific problem
area until the diagnosis system is cancelled.
Note: 1988 and 1989 models are not
equipped with long term memory. It is
possible to access the codes but the operator
must remember to NOT turn the ignition key to
the OFF position after the CHECK ENGINE
light has been noticed. The codes will be lost
and it will be necessary to start the engine and
operate the vehicle through a complete drive
cycle to allow the fault code(s) to be set once
again. Instead of turning the ignition key to the
OFF position, simply stop at position II (key
ON but engine not running) to retain the fault
codes.
6•2 Emissions and engine control systems
3261 Jaguar XJ6
2.10 The ECU is located behind the
passenger’s side glovebox near the footrest
area. Remove the mounting screws
(arrowed) and carefully lower the ECU