1997 JAGUAR XJ6 stereo

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

sure you have the correct activation code
before disconnecting the battery.
2Disconnect the electrical connectors and
the coil wire from the coil.
3Using an ohmmeter, check the coil
resistance:
a) Measure the resistance between the
positive and negative terminals (see
illustration). Compare your reading with
the specified coil primary resistance listed
in this Chapter’s Specifications.
b) Measure the resistance between the
positive terminal and the high tension (HT)
terminal(see illustration). Compare your
reading with the specified coil secondary
resistance listed in this Chapter’s
Specifications.
4If either of the above tests yield resistance
values outside the specified amount, renew
the coil.
Renewal
5Detach 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. 6Label and disconnect the electrical wires
from the coil terminals.
7Remove the coil mounting fasteners (see
illustration).
8Refitting is the reverse of removal.
9 Distributor-
removal and refitting
2
Note:The timing on this ignition system cannot
be adjusted by turning the distributor. Ignition
timing is maintained by the ECU at all times. In
the event the distributor must be removed from
the engine, be sure to follow the precautions
described in this section and mark the engine
and distributor with paint to ensure correct
refitting. If the distributor is not marked, and the
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.
Removal
1Detach 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.
2Disconnect the electrical connectors from
the distributor.
3Look for a raised “1” on the distributor cap.
This marks the location for the number one
cylinder spark plug lead terminal. If the cap
does not have a mark for the number one
terminal, locate the number one spark plug
and trace the wire back to the terminal on the
cap.
4Remove the distributor cap (see Chapter 1)
and rotate the engine until the rotor is pointing
toward the number one spark plug terminal.
5Make a mark on the edge of the distributor
base directly below the rotor tip and in line
with it. Also, mark the distributor base and the
engine block to ensure that the distributor is
installed correctly (see illustrations).
6Remove the distributor hold-down bolt,
then pull the distributor out to remove it.
Caution: DO NOT turn the crankshaft while
the distributor is out of the engine, or the
alignment marks will be useless.
5•4 Engine electrical systems
8.3a To check the primary resistance of
the coil, measure the resistance between
the positive and the negative terminals8.3b To check the secondary resistance of
the coil, measure the resistance between
the positive terminal and the HT terminal8.7 Remove the nuts from the coil
mounting bracket (arrowed)
3261 Jaguar XJ6
9.5a Paint or scribe a mark (arrowed) on the edge of the
distributor housing below the rotor tip to ensure that the rotor is
pointing in the same direction when the distributor is reinstalled9.5b Paint or scribe another mark across the cylinder head and
the distributor body (arrowed) to ensure that the distributor is
aligned correctly when it is reinstalled

model but the designations are the same.
Refer to the wiring diagrams at the end of
Chapter 12.
f) Start the engine and check the alternator
for abnormal noises (a shrieking or
squealing sound indicates a bad bushing).
g) Check the specific gravity of the battery
electrolyte. If it’s low, charge the battery
(doesn’t apply to maintenance free
batteries).
h) Make sure that the battery is fully charged
(one bad cell in a battery can cause
overcharging by the alternator).
i) Disconnect the battery cables (negative
first, then positive). 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. Inspect the
battery posts and the cable clamps for
corrosion. Clean them thoroughly if
necessary (see Chapter 1). Reconnect the
positive cable, then the negative cable.
2Using a voltmeter, check the battery
voltage with the engine off. It should be
approximately 12 volts (see illustration).
3Start the engine and check the battery
voltage again. It should now be approximately
13.5 to 15.1 volts.
4Turn on the headlights. The voltage should
drop and then come back up, if the charging
system is working properly.
5If the voltage reading is greater than the
specified charging voltage, renew the
alternator.
6If you have an ammeter, connect it up to the
charging system according to its maker’s
instructions. If you don’t have a professional-
type ammeter, you can also use an inductive-
type current indicator. This device is
inexpensive, readily available at car accessory
outlets and accurate enough to perform simple
amperage checks like the following test.7With the engine running at 2000 rpm, check
the reading on the ammeter with all
accessories and lights off (no load), then again
with the high-beam headlights on and the
heater blower switch turned to the HI position
(full load). Compare your readings to the
standard amperage listed in this Chapter’s
Specifications.
8If the ammeter reading is less than standard
amperage, repair or renew the alternator.
9If the alternator is working but the charging
system still does function properly, check the
operation of the load dump module (see
illustration). Have this component checked at
a dealer service department.
12 Alternator-
removal and refitting
2
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
sure you have the correct activation code
before disconnecting the battery.2Detach the electrical connectors from the
alternator.
3Loosen the alternator adjustment and pivot
bolts (see illustration) and detach the
drivebelt.
4Remove the adjustment and pivot bolts
(see illustration)from the alternator
adjustment bracket.
5If you are replacing the alternator, take the
old alternator with you when purchasing a
replacement unit. Make sure that the
new/rebuilt unit is identical to the old
alternator. Look at the terminals - they should
be the same in number, size and locations as
the terminals on the old alternator. Finally,
look at the identification markings - they will
be stamped in the housing or printed on a tag
or plaque affixed to the housing. Make sure
that these numbers are the same on both
alternators.
6Many new/rebuilt alternators do not have
a pulley installed, so you may have to switch
the pulley from the old unit to the new/rebuilt
one. When buying an alternator, find out the
policy regarding refitting of pulleys - some
shops will perform this service free of charge.
7Refitting is the reverse of removal.
5•6 Engine electrical systems
12.3 Loosen the lock bolt and back-off
the adjustment bolt (arrowed) to remove
the drivebelt12.4 Remove the pivot bolt and nut
3261 Jaguar XJ6 11.2 Connect the probes of a voltmeter to the battery terminals
and observe battery voltage with the engine OFF
and then with the engine running
11.9 The load dump module is located on the bulkhead
next to the MAF sensor

8After the alternator is installed, adjust the
drivebelt tension (see Chapter 1).
9Check the charging voltage to verify proper
operation of the alternator (see Section 11).
13 Starting system- general
information and precautions
The sole function of the starting system is
to crank the engine over quickly enough to
allow it to start.
The starting system consists of the battery,
the starter motor, the starter solenoid, the
starter relay and the electrical circuit
connecting the components. The solenoid is
mounted directly on the starter motor.
The solenoid/starter motor assembly is
installed on the upper part of the engine, next
to the transmission bellhousing.
When the ignition key is turned to the
START position, the starter solenoid is
actuated through the starter control circuit.
The starter solenoid then connects the battery
to the starter. The battery supplies the
electrical energy to the starter motor, which
does the actual work of cranking the engine.
The starter on a vehicle equipped with an
automatic transmission can be operated only
when the transmission selector lever is in Park
or Neutral.
These vehicles are equipped with either a
Bosch or Lucas starter assembly. The Lucas
unit is distinguished by the separate earth
strap from the solenoid to the starter body.
Bosch starter assemblies are equipped with a
solid metal earthing bar.
The starting system circuit is equipped with
a relay. The relay allows the ignition switch to
power the starter solenoid.
Always observe the following precautions
when working on the starting system:
a) Excessive cranking of the starter motor
can overheat it and cause serious
damage. Never operate the starter motor
for more than 15 seconds at a time
without pausing to allow it to cool for at
least two minutes.
b) The starter is connected directly to the
battery and could arc or cause a fire if
mishandled, overloaded or short circuited.
c) Always detach the cable from the
negative terminal of the battery before
working on the starting 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.
14 Starter motor-
testing in vehicle
2
1Make sure that the battery is charged and
that all cables, both at the battery and starter
solenoid terminals, are clean and secure.2If the starter motor does not turn at all when
the switch is operated, make sure that the
shift lever is in Neutral or Park (automatic
transmission) or that the clutch pedal is
depressed (manual transmission).
3If the starter motor spins but the engine is
not cranking, the overrunning clutch in the
starter motor is slipping and the starter motor
must be renewed.
4If, when the switch is actuated, the starter
motor does not operate at all but the solenoid
clicks, then the problem lies with either the
battery, the main solenoid contacts or the
starter motor itself (or the engine is seized).
5If the solenoid plunger cannot be heard
when the switch is actuated, the battery is
bad, the in-line fuse is burned (the circuit is
open), the starter relay (see illustration)is
defective or the starter solenoid itself is
defective.
6To check the solenoid, connect a jumper
lead between the battery (+) and the ignition
switch terminal (the small terminal) on the
solenoid. If the starter motor now operates,
the solenoid is OK and the problem is in the
ignition switch, linear switch (1988 to 1992),
rotary switch (1993 and 1994) or in the wiring.
7If the starter motor still does not operate,
remove the starter/solenoid assembly for
dismantling, testing and repair.
8If the starter motor cranks the engine at an
abnormally slow speed, first make sure that
the battery is charged and that all terminalconnections are tight. If the engine is partially
seized, or has the wrong viscosity oil in it, it
will crank slowly.
9Run the engine until normal operating
temperature is reached, then disconnect the
coil wire from the distributor cap and earth it
on the engine.
10Connect a voltmeter positive lead to the
battery positive post and connect the
negative lead to the negative post.
11Crank the engine and take the voltmeter
readings as soon as a steady figure is
indicated. Do not allow the starter motor to
turn for more than 15 seconds at a time. A
reading of nine volts or more, with the starter
motor turning at normal cranking speed, is
normal. If the reading is nine volts or more but
the cranking speed is slow, the motor is faulty.
If the reading is less than nine volts and the
cranking speed is slow, the solenoid contacts
are probably burned, the starter motor is bad,
the battery is discharged or there is a bad
connection.
15 Starter motor-
removal and refitting
2
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
sure you have the correct activation code
before disconnecting the battery.
2Raise the vehicle and support it securely
using axle stands.
3Drain the transmission fluid (see Chapter 7)
and remove the transmission fluid filler tube
from the transmission.
4Detach the electrical connectors from the
starter/solenoid assembly (see illustrations).
5Place a trolley jack under the tail section of
the transmission, remove the rear trans-
mission mount (see Chapter 7) and lower the
transmission slightly to gain access to the
upper transmission bellhousing bolts. Using
an extension with a swivel socket, remove the
upper starter mounting bolt (see illustration).
Engine electrical systems 5•7
5
14.5 With the ignition key ON (engine not
running), check for battery voltage to the
starter relay
15.4a Disconnect the solenoid electrical
connector at the harness connector
located near the bulkhead behind the
cylinder head (arrowed)15.4b From underneath the vehicle,
remove the battery terminal from the
solenoid (cylinder head removed
for clarity)
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

e) The silicone boot must be installed in the
correct position to prevent the boot from
being melted and to allow the sensor to
operate properly.
Check
13Locate the oxygen sensor electrical
connector and inspect the oxygen sensor
heater. Disconnect the oxygen sensor
electrical connector and connect an
ohmmeter between the two terminals (see
illustration). It should be around 5 to 6 ohms.
14Also, check for proper supply voltage to
the oxygen sensor heater. Measure the voltage
with the electrical connector connected. Insert
a long pin into the backside of the electrical
connector on the correct wire. With the ignition
key ON (engine not running), check for voltage.
There should be approximately 12 volts.
Note:Battery voltage to the heater is supplied
by the main relay (1988 to 1990) or the oxygen
sensor relay (1991 to 1994). Check the
oxygen sensor relay and the wiring harness if
battery voltage is not available to the heater.
Refer to the wiring diagrams at the end of
Chapter 12 and the relay locator schematics
also in Chapter 12.
15Next, check for a millivolt signal from the
oxygen sensor. Locate the oxygen sensor
electrical connector and insert a long pin into
the oxygen sensor signal wire terminal (see
illustration). The SIGNAL wire is the single wire
with the rubber sheath covering its terminal.
16Monitor the voltage signal (millivolts) as
the engine goes from cold to warm.
17The oxygen sensor will produce a steady
voltage signal at first (open loop) of
approximately 0.1 to 0.2 volts with the engine
cold. After a period of approximately two
minutes, the engine will reach operating
temperature and the oxygen sensor will startto fluctuate between 0.1 to 0.9 volts (closed
loop). If the oxygen sensor fails to reach the
closed loop mode or there is a very long
period of time until it does switch into closed
loop mode, or if the voltage doesn’t fluctuate
well (indicating a “lazy” sensor), renew the
oxygen sensor with a new part.
Renewal
Note:Because it is installed in the exhaust
manifold or pipe, which contracts when cool,
the oxygen sensor may be very difficult to
loosen when the engine is cold. Rather than
risk damage to the sensor (assuming you are
planning to reuse it in another manifold or
pipe), start and run the engine for a minute or
two, then shut it off. Be careful not to burn
yourself during the following procedure.
18Disconnect the cable from the negative
terminal of the battery.
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.
19Raise the vehicle and place it securely on
axle stands.
20Disconnect the electrical connectors from
the sensor pigtail lead.
21Unscrew the oxygen sensor from the
exhaust system (see illustration).
Caution: Excessive force may damage the
threads.
22Anti-seize compound must be used on
the threads of the sensor to facilitate future
removal. The threads of new sensors will
already be coated with this compound, but if
an old sensor is removed and reinstalled,
recoat the threads.
23Refit the sensor and tighten it securely.
24Reconnect the electrical connectors to
the main engine wiring harness.25Lower the vehicle and reconnect the cable
to the negative terminal of the battery.
Throttle potentiometer
General description
26The throttle potentiometer is located on
the end of the throttle shaft on the bottom
section of the throttle body. By monitoring the
output voltage from the throttle
potentiometer, the ECU can alter fuel delivery
based on throttle valve angle (driver demand).
A broken or loose throttle potentiometer will
cause bursts of fuel from the injectors and an
unstable idle because the ECU thinks the
throttle is moving. Throttle body removal
procedures are covered in Chapter 4.
Check
27Check for the proper reference voltage to
the throttle potentiometer. Carefully back-
probe the throttle potentiometer electrical
connector using a pin on the reference voltage
wire and ground (see illustration). With the
ignition key ON (engine not running) the
reference voltage should be about 5.0 volts.
Emissions and engine control systems 6•5
6
4.21 Unscrew the oxygen sensor from the
exhaust system
3261 Jaguar XJ6 4.13 To test the oxygen sensor heater, disconnect the electrical
connector, and working on the sensor side, check the resistance
across the two terminals. Heater resistance should be 5 to 6 ohms
4.15 Refit a pin into the backside of the oxygen sensor connector
into the correct terminal and check for a millivolt output signal
generated by the sensor as it warms up. The SIGNAL wire is easily
recognised by the rubber sheath covering the terminal (arrowed)

5 Air Injector Reactor
(AIR) system
General information
1The air injection reactor system reduces
carbon monoxide and hydrocarbon content
in the exhaust gases by injecting fresh air into
the hot exhaust gases leaving the exhaust
ports. When fresh air is mixed with hot
exhaust gases, oxidation is increased,
reducing the concentration of hydrocarbons
and carbon monoxide and converting them
into harmless carbon dioxide and water.
2The air injection system is composed of an
air pump, diverter valve (bypass), check valve,
air injection manifold, vacuum delay valve,
vacuum control solenoid, air pump magnetic
clutch, air pump clutch relay and hoses (see
illustration). The air pump is driven by a belt
from the crankshaft and supplies compressed
air to the exhaust manifold(s). The check valve
prevents the reverse flow of exhaust gases into
the system. The vacuum-operated (early
models) or electrically-operated (later models)air cut-off valve prevents air from being drawn
into the exhaust when the air pump is switched
off. System vacuum to the air cut-off valve is
controlled by the solenoid vacuum valve in
parallel circuit with the air pump. A delay valve
prevents vacuum loss to the solenoid valve
during wide open throttle operation.
3Injected air is controlled by the computer,
the air pump clutch and the air pump clutch
relay. The AIR system is used during warm-up
(58 to 83° F) to control emissions while the
engine is running rich. The oxygen sensor
feedback system cannot function while the AIR
system is operating. The computer controls
both systems during warm-up and operating
temperatures. If problems occur with the
AIR system relay or circuit, the on-board
diagnosis system will set a code 66.
Check
4Check the condition of the air pump
drivebelt, the injection hoses and the injection
manifold. Make sure that all components are
intact and there are no leaks.
5Check the operation of the air pump clutch
relay (see illustration)and the air pump
clutch. First remove the relay and check forbattery voltage to the relay. Also, check the
relay itself. Refer to the relay checking
procedure in Chapter 12. Extract codes from
the self-diagnosis system (see Section 3) and
check for a code 66, AIR relay malfunction.
6Make sure the electrical connector is
securely fastened to the diverter valve (see
illustration). If everything appears OK but a
fault code still sets, have the system
diagnosed by a dealer service department or
other qualified repair workshop.
Air pump renewal
7Disconnect the cable from the negative
terminal of the battery.
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.
8Disconnect the electrical connector from
the air pump clutch.
9Loosen the clips from the air inlet and outlet
hose and separate them from the air injection
pump.
10Loosen the adjuster and pivot bolts (see
illustration)and nuts but do not remove them
from the air injection pump brackets.
6•8 Emissions and engine control systems
3261 Jaguar XJ6 5.2 Schematic of the Air Injection Reactor (AIR) system
5.6 Location of the AIR diverter valve on a 1992 model - check the
hoses for cracking and the electrical connector for security5.10 Loosen the pivot bolt and then the adjustment nut to remove
the drivebelt from the air pump. The adjustment nut has a lock bolt
that must be loosened before the pump will move down the adjuster
5.5 Location of the AIR pump relay on a 1992 model