1997 JAGUAR XJ6 warning

tank. If there is any doubt about the
amount of fuel in the tank, drain the fuel
tank completely before attempting this
procedure (Section 7, paragraph 1).
9Disconnect the cable from the negative
terminal of the battery. Disconnect the fuel level
sender unit/fuel pump electrical connector.
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.
10Using a brass punch, tap on the lock ring
anti-clockwise (see illustration)until the tabs
align with the indentations in the fuel tank.
11Carefully angle the sender unit out of the
opening without damaging the fuel level float
(see illustration).
12Refitting is the reverse of removal.
6 Fuel lines and fittings-
inspection and renewal
2
Warning: Petrol is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. See
the Warning in Section 2.
Note:If there is a distinct knocking noise
coming from the dash when the engine is
idling, the fuel feed hose may have hardened,
restricting fuel flow and causing abnormal
sounds. Replace the fuel inlet (feed) hose with
a new one.
Inspection
1Once in a while, you will have to raise the
vehicle to service or renew some component
(an exhaust pipe hanger, for example).
Whenever you work under the vehicle, always
inspect fuel lines and all fittings and
connections for damage or deterioration.
2Check all hoses and pipes for cracks, kinks,
deformation or obstructions.
3Make sure all hoses and pipe clips attach
their associated hoses or pipes securely to
the underside of the vehicle.4Verify all hose clamps attaching rubber
hoses to metal fuel lines or pipes are a tight fit
between the hoses and pipes.
Renewal
5If you must renew any damaged sections,
use hoses or pipes constructed from exactly
the same material as the section you are
replacing. Do not refit substitutes constructed
from inferior or inappropriate material or you
could cause a fuel leak or a fire.
6Always, before detaching or disassembling
any part of the fuel line system, note the
routing of all hoses and pipes and the
orientation of all clamps and clips to assure
that new sections are identically installed.
7Before detaching any part of the fuel
system, be sure to relieve the pressure in the
tank by removing the fuel tank cap, then
relieve the fuel system pressure (Section 2).
Cover the fitting being disconnected with a
rag to absorb any fuel that may leak out.
7 Fuel tank-
removal and refitting
3
Warning: Petrol is extremely
flammable, so take extra
precautions when you work onany part of the fuel system. See the
Warning in Section 2.
1This procedure is much easier to perform if
the fuel tank is empty. Some models may have
a drain plug for this purpose. If for some reason
the drain plug can’t be removed, postpone the
job until the tank is empty or siphon the fuel
into an approved container using a siphoning
kit (available at most motor factors).
Warning: Do not start the
siphoning action by mouth!
2Remove the fuel filler cap to relieve fuel
tank pressure.
3Detach the battery negative cable.
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.
4If the tank is full or nearly full, drain the fuel
into an approved container.
5Raise the vehicle and place it securely on
axle stands.
6Remove the filler neck vent tube clamp (see
illustration)and separate the tube from the
fuel filler neck.
7Remove the fuel filler assembly bolts (see
illustration)and slide the large rubber boot
down the neck of the fuel tank. Note:These
vehicles are susceptible to clogging of the fuel
overflow line. If this happens, excess fuel or
4•6 Fuel and exhaust systems
7.6 Remove the clamp that retains the fuel
filler assembly to the filler neck7.7a Remove bolts (arrowed) that retain the
fuel filler assembly to the body and slide the
assembly down the filler neck of fuel tank
3261 Jaguar XJ6 5.10 Use a brass punch and remove the lock ring by tapping on it
in an anti-clockwise direction
5.11 Lift the fuel level sender unit assembly from the fuel tank at
an angle so as not to damage the float or arm

of these sensors and their corresponding
ECU-controlled relays are not contained
within EFI components, but are located
throughout the engine compartment. For
further information regarding the ECU and its
relationship to the engine electrical and
ignition system, see Chapter 6.
12 Electronic Fuel Injection
(EFI) system- check
2
1Check the earth wire connections for
tightness. Check all wiring and electrical
connectors that are related to the system.
Loose electrical connectors and poor grounds
can cause many problems that resemble
more serious malfunctions.
2Check to see that the battery is fully
charged, as the control unit and sensors
depend on an accurate supply voltage in
order to properly meter the fuel.
3Check the air filter element - a dirty or
partially blocked filter will severely impede
performance and economy (see Chapter 1).
4If a blown fuse is found, renew it and see if
it blows again. If it does, search for a shorted
wire in the harness related to the system.
5Check the air intake duct from the MAF
sensor to the intake manifold for leaks, which
will result in an excessively lean mixture. Also
check the condition of the vacuum hoses
connected to the intake manifold.
6Remove the air intake duct from the throttle
body and check for carbon and residue build-
up. If it’s dirty, clean with aerosol carburettor
cleaner (make sure the can says it’s safe for
use with oxygen sensors and catalytic
converters) and a toothbrush.
7With the engine running, place a
stethoscope against each injector, one at a
time, and listen for a clicking sound, indicating
operation (see illustration).8If there is a problem with an injector,
purchase a special injector test light (noid
light) and refit it into the injector electrical
connector (see illustration). Start the engine
and make sure that each injector connector
flashes the noid light. This will test for the
proper voltage signal to the injector.Caution:
If the engine will not start and the noid
light indicates that each injector is
receiving the proper signal, there is a good
possibility that the injector(s) is stuck open
and allowing fuel into the combustion
chamber in excessive amounts. If the spark
plugs are fouled, detach the primary (low
voltage) wires from the ignition coil, disable
the fuel pump by removing the fuel pump
relay (see Section 2), remove the spark plugs
and crank the engine over. If fuel sprays from
the spark plug holes, the engine is flooded
and the fuel must be removed from the
combustion chambers.
9With the engine OFF and the fuel injector
electrical connectors disconnected, measure
the resistance of each injector (see
illustration). Each injector should measure
about 2.0 to 3.0 ohms. If not, the injector is
probably faulty.10The remainder of the system checks
should be left to a Jaguar service department
or other qualified repair workshop, as there is
a chance that the control unit may be
damaged if not performed properly.
13 Electronic Fuel Injection
(EFI) system- component
check and renewal
3
Warning: Petrol is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. See
the Warning in Section 2.
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.
Throttle body
Check
1Verify that the throttle linkage operates
smoothly.
2Start the engine, detach each vacuum hose
and, using your finger, check the vacuum at
each port on the throttle body with the engine
at idle and above idle. The vacuum available
from the throttle body is ported. Raise the
engine rpm and watch as vacuum increases.
It may be necessary to use a vacuum gauge.
Refer to Chapter 2B for additional information
concerning vacuum checks.
Renewal
Warning: Wait until the engine is
completely cool before
beginning this procedure.
3Detach the cable from the negative terminal
of the battery (see the Cautionat the
beginning of this Section).
4Drain the radiator (see Chapter 1).
4•10 Fuel and exhaust systems
12.9 Using an ohmmeter, measure the
resistance across both terminals
of the injector
3261 Jaguar XJ6 12.7 Use a stethoscope or a screwdriver to determine if the
injectors are working properly - they should make a steady
clicking sound that rises and falls with engine speed changes
12.8 Refit the “noid” light into the fuel injector electrical
connector and check to see that it blinks with the engine running

manifold as a single unit and have it repaired
by a dealer service department. Refer to
Chapter 2 for removal and refitting procedures.
14 Exhaust system servicing-
general information
Warning: Inspection and repair
of exhaust system components
should be done only after the
components have cooled.
1The exhaust system consists of the exhaust
manifold, catalytic converter, the silencer, the
tailpipe and all connecting pipes, brackets,
hangers and clamps. The exhaust system is
attached to the body with mounting brackets
and rubber hangers (see illustrations). If any
of these parts are damaged or deteriorated,
excessive noise and vibration will be
transmitted to the body. Note:The exhaust
system configuration changes with later model
updates. Earlier models (1988 and 1989) are
equipped with a pre-catalytic converter near
the exhaust manifold incorporating a single
exhaust pipe to the silencer. Later models are
equipped with dual exhaust pipes, dual
catalytic converters and silencers.
2Conducting regular inspections of the
exhaust system will keep it safe and quiet.
Look for any damaged or bent parts, open
seams, holes, loose connections, excessive
corrosion or other defects which could allow
exhaust fumes to enter the vehicle.
Deteriorated exhaust system components
should not be repaired - they should be
replaced with new parts.
3If the exhaust system components are
extremely corroded or rusted together, they
will probably have to be cut from the exhaust
system. The convenient way to accomplish
this is to have a silencer repair workshop
remove the corroded sections with a cutting
torch. If, however, you want to save money by
doing it yourself and you don’t have an
oxy/acetylene welding outfit with a cutting
torch, simply cut off the old components with
a hacksaw. If you have compressed air,
special pneumatic cutting chisels can also beused. If you do decide to tackle the job at
home, be sure to wear eye protection to
protect your eyes from metal chips and work
gloves to protect your hands.
4Here are some simple guidelines to apply
when repairing the exhaust system:
a) Work from the back to the front when
removing exhaust system components.
b) Apply penetrating oil to the exhaust
system component fasteners to make
them easier to remove(see illustration).
c) Use new gaskets, hangers and clamps
when refitting exhaust system components.
d) Apply anti-seize compound to the threads
of all exhaust system fasteners during
reassembly.e) Be sure to allow sufficient clearance
between newly installed parts and all
points on the underbody to avoid
overheating the floor pan and possibly
damaging the interior carpet and
insulation. Pay particularly close attention
to the catalytic converter and its heat
shield.
Warning: The catalytic converter
operates at very high tem-
peratures and takes a long time
to cool. Wait until it’s completely
cool before attempting to remove the
converter. It’s a good idea to wear suitable
gloves. Failure to observe these points
could result in serious burns.
4•14 Fuel and exhaust systems
14.1c On dual silencer models, check the
condition of the mount (arrowed)
and the clamps
14.1a The rear tailpipe section is fastened
to the chassis with a special rubber mount
(arrowed) that pivots with road movement.
Check for deterioration and alignment14.1b Check the condition of the flexible
rubber mounts that hang the silencer to
the chassis
14.4 Use penetrating spray on the exhaust
flange nuts before attempting to
remove them
3261 Jaguar XJ6

same dimensions, amperage rating, cold
cranking rating, etc. as the original.
6Refitting is the reverse of removal.
4 Battery cables-
check and renewal
1
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.
1Periodically inspect the entire length of
each battery cable for damage, cracked or
burned insulation and corrosion. Poor battery
cable connections can cause starting
problems and decreased engine performance.
2Check the cable-to-terminal connections at
the ends of the cables for cracks, loose wire
strands and corrosion. The presence of white,
fluffy deposits under the insulation at the
cable terminal connection is a sign that the
cable is corroded and should be renewed.
Check the terminals for distortion, missing
mounting bolts and corrosion.
3When removing the cables, always
disconnect the negative cable first and hook it
up last or the battery may be shorted by the
tool used to loosen the cable clamps. Even if
only the positive cable is being renewed, be
sure to disconnect the negative cable from
the battery first (see Chapter 1 for further
information regarding battery cable removal).
4Disconnect the cables from the battery,
then trace each of them to their opposite ends
and detach them from the starter solenoid
and earth terminals. Note the routing of each
cable to ensure correct refitting.
5If you are replacing either or both of the old
cables, take them with you when buying new
items. It is vitally important that you replace
the cables with identical parts. Cables have
characteristics that make them easy to
identify: positive cables are usually red, larger
in cross-section and have a larger diameter
battery post clamp; earth cables are usually
black, smaller in cross-section and have a
slightly smaller diameter clamp for the
negative post.
6Clean the threads of the solenoid or earth
connection with a wire brush to remove rust
and corrosion. Apply a light coat of battery
terminal corrosion inhibitor, or petroleum jelly,
to the threads to prevent future corrosion.
7Attach the cable to the solenoid or earth
connection and tighten the mounting nut/bolt
securely.
8Before connecting a new cable to the
battery, make sure that it reaches the battery
post without having to be stretched.
9Connect the positive cable first, followed by
the negative cable.
5 Ignition system- general
information and precautions
1All models are equipped with a computerised
ignition system. The ignition system consists of
the ignition coil, the crankshaft position sensor,
the amplifier and the electronic control unit
(ECU). The ignition ECU controls the ignition
timing and advance characteristics for the
engine. The ignition timing is not adjustable,
therefore, changing the position of the distributor
will not change the timing in any way. Note:In
the event the distributor must be removed from
the engine, be sure to follow the precautions
described in Section 9 and mark the engine and
distributor with paint to ensure correct refitting. If
the distributor is not marked and Ihe crankshaft is
turned while the distributor is out of the engine,
have the distributor installed by a dealer service
department. The distributor must be installed
using a special alignment tool.
2The distributor is driven by the intermediate
shaft which also drives the power steering pump.
The crankshaft position sensor is located on the
front timing cover. It detects crank position by
pulsing an electronic signal to the ECU. This
signal is sent to the ECU to provide ignition
timing specifications.
3The computerised ignition system provides
complete control of the ignition timing by
determining the optimum timing in response to
engine speed, coolant temperature, throttle
position and vacuum pressure in the intake
manifold. These parameters are relayed to the
ECU by the crankshaft position sensor, throttle
potentiometer, coolant temperature sensor and
MAF sensor. Ignition timing is altered during
warm-up, idling and warm running conditions by
the ECU. This electronic ignition system also
consists of the ignition switch, battery, coil,
distributor, spark plug leads and spark plugs.
4Refer to a dealer parts department or car
accessory outlet for any questions concerning
the availability of the distributor parts and
assemblies. Testing the crankshaft position
sensor is covered in Chapter 6.
5When working on the ignition system, take
the following precautions:
a) Do not keep the ignition switch on for
more than 10 seconds if the engine will
not start.
b) Always connect a tachometer in
accordance with the manufacturer’s
instructions. Some tachometers may be
incompatible with this ignition system.
Consult a dealer service department
before buying a tachometer for use with
this vehicle.
c) Never allow the ignition coil terminals to
touch earth. Earthing the coil could result
in damage to the igniter and/or the
ignition coil.
d) Do not disconnect the battery when the
engine is running.
6 Ignition system- check
2
Warning: Because of the high
voltage generated by the
ignition system, extreme care
should be taken when working
on the ignition components. This not only
includes the amplifier, coil, distributor and
spark plug leads, but related components
such as connectors, tachometer and other
test equipment also.
1With the ignition switch turned to the “ON”
position, a “Battery” light or an “Oil Pressure”
light is a basic check for ignition and battery
supply to the ECU.
2Check all ignition wiring connections for
tightness, cuts, corrosion or any other signs of a
bad connection.
3Use a calibrated ignition tester to verify
adequate secondary voltage (25,000 volts) at
each spark plug (see illustration). A faulty or
poor connection at that plug could also result in a
misfire. Also, check for carbon deposits inside
the spark plug boot.
4Check for carbon tracking on the coil. If
carbon tracking is evident, renew the coil and be
sure the secondary wires related to that coil are
clean and tight. Excessive wire resistance or
faulty connections could damage the coil.
5Check for battery voltage to the ignition coil
(see illustration). If battery voltage is available,
check the ignition coil primary and secondary
resistance (see Section 8).
6Check the distributor cap for any obvious
signs of carbon tracking, corroded terminals or
cracks (see Chapter 1).
7Using an ohmmeter, check the resistance of
the spark plug leads. Each wire should measure
less than 25,000 ohms.
8Check for battery voltage to the ignition
amplifier (see Section 7). If battery voltage does
not exist, check the circuit from the ignition
switch (refer to the wiring diagrams at the end of
Chapter 12).
5•2 Engine electrical systems
6.3 To use a calibrated ignition tester
(available at most car accessory outlets),
remove a plug lead from a cylinder,
connect the spark plug boot to the tester
and clip the tester to a good earth - if there
is enough voltage to fire the plug, sparks
will be clearly visible between the
electrode tip and the tester body
3261 Jaguar XJ6

9Check for battery voltage to the Ignition ON
relay (see illustration). If battery voltage does
not exist, check the circuit from the ignition ON
relay to the battery (refer to the wiring diagrams
at the end of Chapter 12). Note:See Chapter 12
for the location of the Ignition ON relay.
10Check the operation of the crankshaft
position sensor (see Chapter 6).
11If all the checks are correct, check the
voltage signal from the computer. Using an LED
type test light, backprobe the coil power lead
(negative terminal) on the ignition coil (see
illustration). Remove the coil secondary wire
and earth the terminal to the engine. Now have
an assistant crank the engine over and observe
that the test light pulses on and off. If there is no
flashing from the test light, most likely the
computer is damaged. Have the ECU diagnosed
by a dealer service department.
12Additional checks should be performed by a
dealer service department or an automotive
repair workshop.
7 Amplifier- check and renewal
2
Warning: Because of the high
voltage generated by the
ignition system, extreme care
should be taken whenever an
operation is performed involving ignitioncomponents. This not only includes the
amplifier, coil, distributor and spark plug
leads, but related components such as
connectors, tachometer and other test
equipment also.
Note:Because of the complexity and the
special tools required to test the amplifier, the
following procedure only describes a test to
verify battery voltage is reaching the amplifier.
If the wiring harness and the relays are
working properly and battery voltage is
available to the amplifier, have the ignition
system and the ECU diagnosed by a dealer
service department.
Check
1Disconnect the amplifier electrical connector
(see illustration).
2Turn the ignition key ON (engine not
running), check for battery voltage (see
illustration) to the amplifier.
3If no battery voltage is present, check the
harness from the ignition switch to the
amplifier. Refer to the wiring diagrams at the
end of Chapter 12.
Renewal
4Disconnect the negative battery terminal.
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.5Remove the amplifier mounting bolts (see
illustration).
6Refitting is the reverse of removal.
8 Ignition coil-
check and renewal
2
Check
1Detach the cable from the negative terminal
of the battery.
Caution: If the stereo in your vehicle is
equipped with an anti-theft system, make
Engine electrical systems 5•3
5
6.5 Check for battery voltage to the
coil (+) terminal6.9 Check for battery voltage
to the IGN ON relay6.11 Refit the LED test light to the coil
negative (-) terminal, crank the engine over
and observe the light flash in response to
the trigger signal from the computer
7.1 Remove the clip that retains the
harness connector to the amplifier7.2 Check for battery voltage to the
ignition amplifier
7.5 Remove the amplifier mountings
screws (arrowed) and lift the unit from the
engine compartment
3261 Jaguar XJ6

Refitting
7Insert the distributor into the engine in
exactly the same relationship to the block that
it was in when removed.
8If the distributor does not seat completely,
recheck the alignment marks between the
distributor base and the block to verify that
the distributor is in the same position it was in
before removal. Also check the rotor to see if
it’s aligned with the mark you made on the
edge of the distributor base.
9Refit the distributor hold-down bolt(s).
10The remainder of refitting is the reverse of
removal.
10 Charging system- general
information and precautions
The charging system includes the alternator,
an internal voltage regulator, a charge
indicator light, load dump module, the battery,
an ignition ON relay, an in-line fuse and the
wiring between all the components (see
illustration). The charging system supplies
electrical power for the ignition system, the
lights, the radio, etc. The alternator is driven by
a drivebelt at the front of the engine.
The purpose of the voltage regulator is to
limit the alternator’s voltage to a preset value.
This prevents power surges, circuit overloads,
etc., during peak voltage output.
The alternator load dump module protects
the electrical circuits from excessive voltage
surges. When the battery cables are removed
large amounts of transient voltage is released
through the electrical circuits. This device
diverts up to 30 load volts of excess voltage to
earth by way of a voltage dependent resistor.
The in-line fuse is a special fuse installed
into the circuit with the engine compartment
wiring harness (see Chapter 12). The in-line
fuse protects the electrical system in the
event of excess voltage surges or a power to
earth short circuit. Refer to Chapter 12 for
additional information concerning the in-line
fuses and their locations.
1993 and 1994 models have a Starter Logic
Relay. This microprocessor (computer)
gathers information from the ignition switch,
linear gear position switch, park/neutral
switch, the security switch and the electronic
door lock system. If all the conditions are in
order, the computer allows battery voltage to
be transferred from the ignition switch to the
starter/solenoid assembly.
The charging system doesn’t ordinarily
require periodic maintenance. However, the
drivebelt, battery and wires and connections
should be inspected at the intervals outlined
in Chapter 1.
The dashboard warning light should come
on when the ignition key is turned to Start,
then should go off immediately. If it remains
on, there is a malfunction in the charging
system. Some vehicles are also equipped with
a voltage gauge. If the voltage gaugeindicates abnormally high or low voltage,
check the charging system (see Section 11).
Be very careful when making electrical
circuit connections to a vehicle equipped with
an alternator and note the following:
a) When reconnecting wires to the alternator
from the battery, note their polarity.
b) Before using arc welding equipment to
repair any part of the vehicle, disconnect
the wires from the alternator and the
battery terminals.
c) Never start the engine with a battery
charger connected.
d) Always disconnect both battery leads
before using a battery charger.
e) The alternator is driven by an engine
drivebelt which could cause serious injury
if your hand, hair or clothes become
entangled in it with the engine running.
f) Because the alternator is connected
directly to the battery, it could arc or
cause a fire if overloaded or shorted out.
g) Wrap a plastic bag over the alternator and
secure it with rubber bands before steam
cleaning the engine.
11 Charging system- check
2
Note:1993 and 1994 models are equipped
with a Starter Logic Relay. This microprocessor
(computer) gathers information from theignition switch, linear gear position switch,
park/neutral switch, the security switch and the
electronic door lock system. If all the conditions
are in order, the computer allows battery
voltage to be transferred from the ignition
switch to the starter/solenoid assembly. If all
the components of the charging system are
working properly and the system still does not
charge properly, have the Starter Logic Relay
diagnosed by a dealer service department.
1If a malfunction occurs in the charging
circuit, don’t automatically assume that the
alternator is causing the problem. First check
the following items:
a) Check the drivebelt tension and its
condition. Renew it if worn or damaged.
b) Make sure the alternator mounting and
adjustment bolts are tight.
c) Inspect the alternator wiring harness and
the electrical connectors at the alternator
and voltage regulator. They must be in
good condition and tight.
d) Check the fusible link (if equipped)
located between the starter solenoid and
the alternator or the large main fuses in
the engine compartment. If it’s burned,
determine the cause, repair the circuit
and renew the link or fuse (the vehicle
won’t start and/or the accessories won’t
work if the fusible link or fuse blows).
e) Check all the in-line fuses that are in series
with the charging system circuit (see
Chapter 12).The location of these fuses
and fusible links may vary from year and
Engine electrical systems 5•5
5
10.1 Schematic of a typical charging system
3261 Jaguar XJ6

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

2The CHECK ENGINE warning light, which is
located on the instrument panel, comes on
when the ignition switch is turned to ON and
the engine is not running. When the engine is
started, the warning light should go out. If the
light remains on, the self-diagnosis system
has detected a malfunction. Note: The
CHECK ENGINE light on early models is
displayed on the dashboard VCM panel on the
right side. Later models are equipped with a
separate CHECK ENGINE light on the left side
of the instrument cluster.Note:Not all the
codes will cause the CHECK ENGINE light to
activate. When performing any fuel or
emissions systems diagnosis, always check
for codes that may be stored but not indicated
by the CHECK ENGINE light.
Obtaining fault code output
3To obtain an output of diagnostic codes,
verify first that the battery voltage is above 11
volts, the throttle is fully closed, the
transmission is in Park, the accessory
switches are off and the engine is at normal
operating temperature.
4Turn the ignition switch to ON but don’t
start the engine (Position II). Note:On 1988
and 1989 models, remember to turn the
ignition switch to position II without turning
the key to OFF.
5Press the VCM button on the display panel
(see illustration)and observe the LED display
on the dash for the designated codes. An
asterisk next to the code indicates that there
are multiple codes stored.
6The numerical values will be displayed on
the trip computer display on the dashboard.
7If there are any malfunctions in the system,
the corresponding fault codes are displayed in
numerical order, lowest to highest.
Cancelling a diagnostic code
8After the faulty component has been
repaired/renewed, the fault code(s) stored in
computer memory must be cancelled.
a) On 1988 to 1991 vehicles, simply drive
the vehicle faster than 19 mph and the
computer will automatically erase the
stored fault code from memory.b) On 1992 to 1994 models, disconnect the
negative battery lead for 30 seconds or
more to erase the stored fault codes.
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.
9A stored code can also be cancelled on
early models by removing the cable from the
battery negative terminal, but other items with
memory (such as the clock and radio presets)
will also be cancelled.
10If the diagnosis code is not cancelled, it
will be stored by the ECU and appear with any
new codes in the event of future trouble.
11Should it become necessary to work on
engine components requiring removal of the
battery terminal, always check to see if a
diagnostic code has been recorded before
disconnecting the battery.
4 Information sensors
Note: Refer to Chapters 4 and 5 for additional
information on the location and the diagnostic
procedures for the output actuators (ISC
motor, air supplementary valve, distributor,
amplifier, etc.) that are not directly covered in
this section.
Coolant temperature sensor
General description
1The coolant temperature sensor is a
thermistor (a resistor which varies the value of
its voltage output in accordance with
temperature changes) which is threaded into
the thermostat housing. As the sensor
temperature DECREASES, the resistance
values will INCREASE. As the sensor
Emissions and engine control systems 6•3
6
3.5 To access the self-diagnosis system
fault codes, locate the VCM button on the
dash and with the ignition key ON (engine
not running) press it to display the codes
3261 Jaguar XJ6
Fault code chart for 1988 and 1989 models
Code System affected Probable cause
1 Oxygen sensor Open oxygen sensor circuit
2 Airflow sensor Not in operating range
3 Coolant temperature sensor Not in operating range
4 Oxygen sensor System indicates full rich
5 Throttle potentiometer/airflow sensor Low throttle potentiometer signal
with high airflow sensor signal
6 Throttle potentiometer/airflow sensor High throttle potentiometer signal
with low airflow sensor signal
7 Throttle potentiometer Idle fuel adjustment failure
8 Intake air temperature sensor Open or shorted circuit in IAT sensor
harness
Fault code chart for 1990 to 1994 models
Code System affected Probable cause
11 Idle potentiometer Not in operating range
12 Airflow sensor Not in operating range
14 Coolant temperature sensor Not in operating range
16 Air temperature sensor Not in operating range
17 Throttle potentiometer Not in operating range
18 Throttle potentiometer/airflow sensor Signal resistance low
at wide open throttle
19 Throttle potentiometer/airflow sensor Signal resistance high at idle
22 Heated oxygen sensor Open or short circuit
22 Fuel pump circuit Open or short circuit
23 Fuel supply Rich exhaust Indicated
24 Ignition amplifier circuit Open or short circuit
26 Oxygen sensor circuit Lean exhaust/vacuum leak
29 ECU Self check
33 Fuel injector circuit Open or short circuit
34 Fuel injector circuit Faulty injector indicated
37 EGR solenoid circuit Short or open circuit
39 EGR circuit Faulty system operation
44 Oxygen sensor circuit Rich or lean condition
46 Idle speed control valve - (coil 1) Open or short circuit
47 Idle speed control valve - (coil 2) Open or short circuit
48 Idle speed control valve Not within specification
68 Road speed sensor Incorrect signal voltage
69 Neutral safety switch circuit Engine cranks in Drive
(adjust or renew switch)
89 Purge control valve circuit Open or short circuit