Ford Mondeo (petrol engines). Manual - part 97

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 processes
this information, and then sends a command
to the fuel injection system, telling it to change
the air/fuel mixture; the end result is an air/fuel
mixture ratio which is constantly maintained
at a predetermined ratio, regardless of driving
conditions. This happens in a fraction of a
second, and goes on almost all the time while
the engine is running - the exceptions are that
the ECU cuts out the system and runs the
engine on values pre-programmed
(“mapped”) into its memory both while the
oxygen sensor is reaching its normal
operating temperature after the engine has
been started from cold, and when the throttle
is fully open for full acceleration.

In the event of a sensor malfunction, a

back-up circuit will take over, to provide
driveability until the problem is identified and
fixed.

Precautions

(a) Always disconnect the power by

uncoupling the battery terminals - see
Section 1 of Chapter 5 - before removing
any of the electronic control system’s
electrical connectors.

(b) When installing a battery, be particularly

careful to avoid reversing the positive and
negative battery leads.

(c) Do not subject any components of the

system (especially the ECU)  to severe
impact during removal or installation.

(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, to test

it (with any kind of test equipment), or to
open its cover.

(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.

General

The various components of the fuel, ignition

and emissions control systems (not forgetting
the same ECU’s control of sub-systems such
as the radiator cooling fan, air conditioning
and automatic transmission, where
appropriate) are so closely interlinked that
diagnosis of a fault in any one component is
virtually impossible using traditional methods.
Working on simpler systems in the past, the
experienced mechanic may well have been
able to use personal skill and knowledge
immediately to pinpoint the cause of a fault, or
quickly to isolate the fault, by elimination;

however, with an engine management system
integrated to this degree, this is not likely to
be possible in most instances, because of the
number of symptoms that could arise from
even a minor fault.

So that the causes of faults can be quickly

and accurately traced and rectified, the ECU
is provided with a built-in self-diagnosis
facility, which detects malfunctions in the
system’s components. When a fault occurs,
three things happen: the ECU identifies the
fault, stores a corresponding code in its
memory, and (in most cases) runs the system
using back-up values pre-programmed
(“mapped”) into its memory; some form of
driveability is thus maintained, to enable the
vehicle to be driven to a garage for attention.

Any faults that may have occurred are

indicated in the form of three-digit codes
when the system is connected (via the built-in
diagnosis or self-test connectors, as
appropriate) to special diagnostic equipment -
this points the user in the direction of the
faulty circuit, so that further tests can pinpoint
the exact location of the fault.

Given below is the procedure that would be

followed by a Ford technician to trace a fault
from scratch. Should your vehicle’s engine
management system develop a fault, read
through the procedure and decide how much
you can attempt, depending on your skill and
experience and the equipment available to
you, or whether it would be simpler to have
the vehicle attended to by your local Ford
dealer. If you are concerned about the
apparent complexity of the system, however,
remember the comments made in the fourth
paragraph of Section 1 of this Chapter; the
preliminary checks require nothing but care,
patience and a few minor items of equipment,
and may well eliminate the majority of faults.
(a) Preliminary checks
(b) Fault code read-out *
(c) Check ignition timing and base idle

speed. Recheck fault codes to establish
whether fault has been cured or not *

(d) Carry out basic check of ignition system

components. Recheck fault codes to
establish whether fault has been cured or
not *

(e) Carry out basic check of fuel system

components. Recheck fault codes to
establish whether fault has been cured or
not *

(f)

If fault is still not located, carry out system
test *

Note: Operations marked with an asterisk
require special test equipment.

Preliminary checks

Note: When carrying out these checks to
trace a fault, remember that if the fault has
appeared only a short time after any part of
the vehicle has been serviced or overhauled,
the first place to check is where that work was
carried out, however unrelated it may appear,
to ensure that no carelessly-refitted
components are causing the problem.

If you are tracing the cause of a “partial”

engine fault, such as lack of performance, in
addition to the checks outlined below, check
the compression pressures (see Part A of
Chapter 2) and bear in mind the possibility
that one of the hydraulic tappets might be
faulty, producing an incorrect valve clearance.
Check also that the fuel filter has been
renewed at the recommended intervals.

If the system appears completely dead,

remember the possibility that the
alarm/inhibitor system may be responsible.
1 The first check for anyone without special
test equipment is to switch on the ignition,
and to listen for the fuel pump (the sound of
an electric motor running, audible from
beneath the rear seats); assuming there is
sufficient fuel in the tank, the pump should
start and run for approximately one or two
seconds, then stop, each time the ignition is
switched on. If the pump runs continuously all
the time the ignition is switched on, the
electronic control system is running in the
back-up (or “limp-home”) mode referred to by
Ford as “Limited Operation Strategy” (LOS).
This almost certainly indicates a fault in the
ECU itself, and the vehicle should therefore be
taken to a Ford dealer for a full test of the
complete system using the correct diagnostic
equipment; do not waste time trying to test
the system without such facilities.
2 If the fuel pump is working correctly (or not
at all), a considerable amount of fault
diagnosis is still possible without special test
equipment. Start the checking procedure as
follows.
3 Open the bonnet and check the condition
of the battery connections - remake the
connections or renew the leads if a fault is
found (Chapter 5). Use the same techniques
to ensure that all earth points in the engine
compartment provide good electrical contact
through clean, metal-to-metal joints, and that
all are securely fastened. (In addition to the
earth connection at the engine lifting eye and
that from the transmission to the
body/battery, there is one earth connection
behind each headlight assembly, and one
below the power steering fluid reservoir.)
4 Referring to the information given in
Chapter 12 and in the wiring diagrams at the
back of this manual, check that all fuses
protecting the circuits related to the engine
management system are in good condition.
Fit new fuses if required; while you are there,
check that all relays are securely plugged into
their sockets.
5 Next work methodically around the engine
compartment, checking all visible wiring, and
the connections between sections of the
wiring loom. What you are looking for at this
stage is wiring that is obviously damaged by
chafing against sharp edges, or against
moving suspension/transmission components
and/or the auxiliary drivebelt, by being
trapped or crushed between carelessly-
refitted components, or melted by being
forced into contact with hot engine castings,

3 Diagnosis system - 

general information

6•4 Emissions control systems

coolant or EGR pipes, etc. In almost all cases,
damage of this sort is caused in the first
instance by incorrect routing on reassembly
after previous work has been carried out (see
the note at the beginning of this sub-Section).
6 Obviously wires can break or short together
inside the insulation so that no visible
evidence betrays the fault, but this usually
only occurs where the wiring loom has been
incorrectly routed so that it is stretched taut or
kinked sharply; either of these conditions
should be obvious on even a casual
inspection. If this is thought to have happened
and the fault proves elusive, the suspect
section of wiring should be checked very
carefully during the more detailed checks
which follow.
7 Depending on the extent of the problem,
damaged wiring may be repaired by rejoining
the break or splicing-in a new length of wire,
using solder to ensure a good connection,
and remaking the insulation with adhesive
insulating tape or heat-shrink tubing, as
desired. If the damage is extensive, given the
implications for the vehicle’s future reliability,
the best long-term answer may well be to
renew that entire section of the loom, however
expensive this may appear.
8 When the actual damage has been
repaired, ensure that the wiring loom is
rerouted correctly, so that it is clear of other
components, is not stretched or kinked, and is
secured out of harm’s way using the plastic
clips, guides and ties provided.
9 Check all electrical connectors, ensuring
that they are clean, securely fastened, and
that each is locked by its plastic tabs or wire
clip, as appropriate. If any connector shows
external signs of corrosion (accumulations of
white or green deposits, or streaks of “rust”),
or if any is thought to be dirty, it must be
unplugged and cleaned using electrical
contact cleaner. If the connector pins are
severely corroded, the connector must be
renewed; note that this may mean the renewal

of that entire section of the loom - see your
local Ford dealer for details.
10 If the cleaner completely removes the
corrosion to leave the connector in a
satisfactory condition, it would be wise to
pack the connector with a suitable material
which will exclude dirt and moisture, and
prevent the corrosion from occurring again; a
Ford dealer may be able to recommend a
suitable product. Note:

The system’s

connectors use gold-plated pins, which must
not be mixed with the older tin-plated types
(readily identifiable from the different colour) if
a component is renewed, nor must the lithium
grease previously used to protect tin-plated
pins be used on gold-plated connectors.
11 Following the accompanying schematic
diagram, and working methodically around
the engine compartment, check carefully that
all vacuum hoses and pipes are securely
fastened and correctly routed, with no signs

of cracks, splits or deterioration to cause air
leaks, or of hoses that are trapped, kinked, or
bent sharply enough to restrict air flow (see
illustrations). Check with particular care at all
connections and sharp bends, and renew any
damaged or deformed lengths of hose.
12 Working from the fuel tank, via the filter, to
the fuel rail (and including the feed and return),
check the fuel lines, and renew any that are
found to be leaking, trapped or kinked.
13 Check that the accelerator cable is
correctly secured and adjusted; renew the
cable if there is any doubt about its condition,
or if it appears to be stiff or jerky in operation.
Refer to the relevant Sections of Chapter 4 for
further information, if required.
14 If there is any doubt about the operation
of the throttle, remove the plenum chamber
from the throttle housing, and check that the
throttle valve moves smoothly and easily from
the fully-closed to the fully-open position and

Emissions control systems  6•5

6

3.11A  Vacuum hose routing schematic diagram

A  Exhaust Gas Recirculation (EGR) solenoid valve
B  Pulse-air solenoid valve
C  Exhaust Gas Recirculation (EGR) exhaust gas pressure

differential sensor

D  Exhaust Gas Recirculation (EGR) valve
E  Charcoal canister-purge solenoid valve
F  Restrictor
G  Idle-increase solenoid valve - where fitted
H  Connection to plenum chamber
J  Connection to inlet manifold
K  Fuel pressure regulator
L  Connection to Positive Crankcase Ventilation (PCV) valve
M  Pulse-air filter housing
N  Connection to heating/air conditioning system controls
P  Charcoal canister

3.11B  Installation of vacuum hoses in engine compartment

back again, as an assistant depresses the
accelerator pedal. If the valve shows any sign
of stiffness, sticking or otherwise-inhibited
movement (and the accelerator cable is
known from the previous check to be in good
condition), spray the throttle linkage with
penetrating lubricant, allow time for it to work,
and repeat the check; if no improvement is
obtained, the complete throttle housing must
be renewed (Chapter 4).
15 Unclip the air cleaner cover, and check
that the air filter element and the crankcase
ventilation system filter are not clogged or
soaked. (A clogged air filter will obstruct the
intake air flow, causing a noticeable effect on
engine performance; a clogged crankcase
ventilation system filter will inhibit crankcase
“breathing”). Renew or clean the filter(s) as
appropriate; refer to the relevant Sections of
Chapter 1 for further information, if required.
Before refitting the air cleaner cover, check
that the air intake (located under the front left-
hand wing, opening behind the direction
indicator/headlight assembly) is clear. It
should be possible to blow through the intake,
or to probe it (carefully) as far as the rear of
the direction indicator light.
16 Start the engine and allow it to idle.
Note: Working in the engine compartment
while the engine is running requires great care
if the risk of personal injury is to be avoided;
among the dangers are burns from contact
with hot components, or contact with moving
components such as the radiator cooling fan
or the auxiliary drivebelt. Refer to “Safety
first!” at the front of this manual before
starting, and ensure that your hands, and long
hair or loose clothing, are kept well clear of hot
or moving components at all times.
17 Working from the air intake junction at the
inner wing panel, via the air cleaner assembly
and air mass meter, to the resonator, plenum
chamber, throttle housing and inlet manifold
(and including the various vacuum hoses and
pipes connected to these), check for air leaks.
Usually, these will be revealed by sucking or
hissing noises, but minor leaks may be traced
by spraying a solution of soapy water on to
the suspect joint; if a leak exists, it will be
shown by the change in engine note and the
accompanying air bubbles (or sucking-in of
the liquid, depending on the pressure
difference at that point). If a leak is found at
any point, tighten the fastening clamp and/or
renew the faulty components, as applicable.
18 Similarly, work from the cylinder head, via
the manifold (and not forgetting the related
EGR and pulse-air system components) to the
tailpipe, to check that the exhaust system is
free from leaks. The simplest way of doing
this, if the vehicle can be raised and
supported safely and with complete security
while the check is made, is to temporarily
block the tailpipe while listening for the sound
of escaping exhaust gases; any leak should
be evident. If a leak is found at any point,
tighten the fastening clamp bolts and/or nuts,
renew the gasket, and/or renew the faulty

section of the system, as necessary, to seal
the leak.
19 It is possible to make a further check of
the electrical connections by wiggling each
electrical connector of the system in turn as
the engine is idling; a faulty connector will be
immediately evident from the engine’s
response as contact is broken and remade. A
faulty connector should be renewed to ensure
the future reliability of the system; note that
this may mean the renewal of that entire
section of the loom - see your local Ford
dealer for details.
20 Switch off the engine. If the fault is not yet
identified, the next step is to check the
ignition voltages, using an engine analyser
with an oscilloscope - without such
equipment, the only tests possible are to
remove and check each spark plug in turn, to
check the spark plug (HT) lead connections
and resistances, and to check the
connections and resistances of the ignition
coil. Refer to the relevant Sections of
Chapters 1 and 5.
21 The final step in these preliminary checks
would be to use an exhaust gas analyser to
measure the CO level at the exhaust tailpipe.

This check cannot be made without special
test equipment - see your local Ford dealer for
details.

Fault code read-out

22 As noted in the general comments at the
beginning of this Section, the preliminary
checks outlined above should eliminate the
majority of faults from the engine
management system. If the fault is not yet
identified, the next step is to connect a fault
code reader to the ECU, so that its self-
diagnosis facility can be used to identify the
faulty part of the system; further tests can
then be made to identify the exact cause of
the fault.
23 In their basic form, fault code readers are
simply hand-held electronic devices, which
take data stored within an ECU’s memory and
display it when required as two- or three-digit
fault codes. The more sophisticated versions
now available can also control sensors and
actuators, to provide more effective testing;
some can store information, so that a road
test can be carried out, and any faults
encountered during the test can be displayed
afterwards.

6•6 Emissions control systems

3.26  Location and terminal identification of engine management system self-test,

diagnosis and service connectors

1  Power steering fluid reservoir
2  Diagnosis connector - for Ford diagnostic equipment FDS 2000
3  Self-test connector - for fault code read-out - pin 17 is output terminal, pin 48 is input 

terminal, pin 40/60 is earth

4  Service connector - for octane adjustment
5  Plug-in bridge - to suit 95 RON fuel

24 Ford specify the use of their STAR (Self-
Test Automatic Readout) tester; most Ford
dealers should have such equipment, and the
staff trained to use it effectively. The only
alternatives are as follows:
(a) To obtain one of those proprietary readers

which can interpret EEC-IV three-digit
codes - at present, such readers are too
expensive for the DIY enthusiast, but are
becoming more popular with smaller
specialist garages.

(b) To use an analogue voltmeter, whereby

the stored codes are displayed as sweeps
of the voltmeter needle. This option limits
the operator to a read-out of any codes
stored - ie, there is no control of sensors
and/or actuators - but can still be useful in
pinpointing the faulty part of the engine
management system. The display is
interpreted as follows. Each code
(whether fault code or
command/separator) is marked by a
three-to-four second pause - code “538”
would therefore be shown as long (3 to 
4 seconds) pause, five fast sweeps of the
needle, slight (1 second) pause, three fast
sweeps, slight pause, eight fast sweeps,
long pause.

(c) Owners without access to such

equipment must take the vehicle to a Ford
dealer, or to an expert who has similar
equipment and the skill to use it.

25 Because of the variations in the design of
fault code readers, it is not possible to give
exact details of the sequence of tests; the
manufacturer’s manuals must be followed,
in conjunction with the codes given below.
The following ten paragraphs outline the
procedure to be followed using a version of
the Ford STAR tester, to illustrate the general
principles, as well as notes to guide the owner
using only a voltmeter.
26 The vehicle must be prepared by applying
the handbrake, switching off the air
conditioning (where fitted) and any other
electrical loads (lights, heated rear window,
etc), then selecting neutral (instruction
transmission) or the “P” position (automatic
transmission). Where the engine is required to
be running, it must be fully warmed-up to
normal operating temperature before the test
is started. Using any adaptors required,
connect the fault code reader to the system
via the (triangular, three-pin) self-test
connector on the right-hand end of the engine
compartment bulkhead (see illustration). If a
voltmeter is being used, connect its positive
lead to the battery positive terminal, and its
negative lead to the self-test connector’s
output terminal, pin 17. Have a pen and paper
ready to write down the codes displayed.
27 Set the tester in operation. For the Ford
STAR tester, a display check will be carried
out and the test mode requirements must be
entered. If a voltmeter is being used, connect
a spare length of wire to earth the self-test
connector’s input terminal, pin 48. Be very
careful to ensure that you earth the correct

terminal - the one with the white/green wire.
The first part of the test starts, with the
ignition switched on, but with the engine off.
On pressing the “Mem/test” button, the tester
displays “TEST” and the ready code “000”,
followed by a command code “010” - the
accelerator pedal must be fully depressed
within 10 seconds of the command code
appearing, or fault codes “576” or “577” will
appear when they are called up later. If a
voltmeter is being used, code “000” will not
appear (except perhaps as a flicker of the
needle) and “010” will appear as a single
sweep - to ensure correct interpretation of the
display, watch carefully for the interval
between the end of one code and the
beginning of the next, otherwise you will
become confused and misinterpret the read-
out.
28 The tester will then display the codes for
any faults in the system at the time of the test.
Each code is repeated once; if no faults are
present, code “111” will be displayed. If a
voltmeter is being used, the pause between
repetitions will vary according to the
equipment in use and the number of faults in
the system, but was found to be
approximately 3 to 4 seconds - it may be
necessary to start again, and to repeat the
read-out until you are familiar with what you
are seeing.
29 Next the tester will display code “010”
(now acting as a separator), followed by the
codes for any faults stored in the ECU’s
memory; if no faults were stored, code “111”
will be displayed.
30 When prompted by the tester, the
operator must next depress the accelerator
pedal fully; the tester then checks several
actuators. Further test modes include a
“wiggle test” facility, whereby the operator
can check the various connectors as
described in paragraph 19 above (in this case,
any fault will be logged and the appropriate
code will be displayed), a facility for recalling
codes displayed, and a means for clearing the
ECU’s memory at the end of the test
procedure when any faults have been
rectified.
31 The next step when using the Ford STAR
tester is to conduct a test with the engine
running. With the tester set in operation (see
paragraph 26 above) the engine is started and
allowed to idle. On pressing the “Mem/test”
button, the tester displays “TEST”, followed
by one of two codes, as follows.
32 If warning code “998” appears, followed
by the appropriate fault code, switch off and
check as indicated the coolant temperature
sensor, the intake air temperature sensor, the
air mass meter, the throttle potentiometer
and/or their related circuits, then restart the
test procedure.
33 If command code “020” appears, carry
out the following procedure within ten
seconds:
(a) Depress the brake pedal fully.
(b) Turn the steering to full-lock (either way)

and centre it again, to produce a signal
from the power steering pressure switch -
if no signal is sent, fault code “521” will
be displayed.

(c) If automatic transmission is fitted, switch

the overdrive cancel button on and off,
then do the same for the
“Economy/Sport” mode switch.

(d) Wait for separator code “010” to be

displayed, then within 10 seconds,
depress the accelerator pedal fully,
increasing engine speed rapidly above
3000 rpm - release the pedal.

34 Any faults found in the system will be
logged and displayed. Each code is repeated
once; if no faults are present, code “111” will
be displayed.
35 When the codes have been displayed for
all faults logged, the ECU enters its “Service
Adjustment Programme”, as follows:
(a) The programme lasts for 2 minutes.
(b) The idle speed control valve is

deactivated, and the idle speed is set to
its pre-programmed (unregulated) value. If
the appropriate equipment is connected,
the base idle speed can be checked
(note, however, that it is not adjustable).

(c) The ignition timing can be checked if a

timing light is connected (note, however,
that it is not adjustable).

(d) Pressing the accelerator pedal fully at any

time during this period will execute a
cylinder balance test. Each injector in turn
is switched off, and the corresponding
decrease in engine speed is logged -
code “090” will be displayed if the test is
successful.

(e) At the end of the 2 minutes, the

completion of the programme is shown
by the engine speed briefly rising, then
returning to normal idling speed as 
the idle speed control valve is 
reactivated.

36 As with the engine-off test, further test
modes include a “wiggle test” facility,
whereby the operator can check the various
connectors as described in paragraph 19
above (in this case, any fault will be logged
and the appropriate code will be displayed), a
facility for recalling codes displayed, and a
means for clearing the ECU’s memory at the
end of the test procedure when any faults
have been rectified. If equipment other than
the Ford STAR tester is used, the ECU’s
memory can be cleared by disconnecting the
battery - if this is not done, the code will
reappear with any other codes in the event of
subsequent trouble, but remember that other
systems with memory (such as the clock and
audio equipment) will also be affected. Should
it become necessary to disconnect the
battery during work on any other part of the
vehicle, first check to see if any fault codes
have been logged.
37 Given overleaf are the possible codes,
their meanings, and where relevant, the action
to be taken as a result of a code being
displayed.

Emissions control systems  6•7

6