Ford Mondeo (petrol engines). Manual - part 36

Code

Meaning

Action

327

EGR system exhaust gas pressure 
differential sensor or solenoid  valve

Check components (Section 6  of this Chapter)

328

EGR system solenoid valve

Check component (Section 6 of this Chapter)

332

EGR valve not opening

Check component (Section 6 of this Chapter)

334

EGR system solenoid valve

Check component (Section 6 of this Chapter)

335

EGR system exhaust gas pressure 
differential sensor

Check component (Section 6 of this Chapter)

336

Exhaust gas pressure too high

Check system (Section 6 of this Chapter)

337

EGR system exhaust gas pressure 
differential sensor or solenoid  valve

Check components (Section 6 of this Chapter)

338, 339

Coolant temperature sensor

Carry out system test (see below)

341

Service connector earthed

Unplug connector and repeat test - reconnect on completion

411

Engine speed too low during test

Check for air leaks, then repeat test

412

Engine speed too high during test

Check for air leaks, then repeat test

413 to 416 Idle speed control valve

Check component (Chapter 4, Section 16)

452

Vehicle speed sensor

Check component (Section 4 of this Chapter)

511, 512

ECU memory

Check whether battery was disconnected, then check fuse 11 - if fault still 
exists, renew ECU (Section 6 of this Chapter)

513

ECU reference voltage

Carry out system test (see below)

519, 521

Power steering pressure switch not 

Check component is fitted and connected, then repeat test - if fault still 

operated during test

exists, carry out system test (see below)

522, 523

Selector lever position sensor

Check component (Chapter 7, Part B)

536

Brake on/off switch not activated 
during test

Repeat test

538

Operator error during test

Repeat test

539

Air conditioning switched on during  test

Switch off and repeat test

542, 543

Fuel pump circuit

Carry out system test (see below)

551

Idle speed control valve circuit

Carry out system test (see below)

552

Pulse-air system circuit

Carry out system test (see below)

556

Fuel pump circuit

Check fuel pump relay - if fault still exists, carry out system test (see below)

558

EGR system solenoid valve circuit

Carry out system test (see below)

563

Radiator (high-speed) electric 
cooling fan relay and/or circuit

Carry out system test (see below)

564

Radiator electric cooling fan relay 
and/or circuit

Carry out system test (see below)

565

Charcoal canister-purge solenoid  valve

Check component (Section 5 of this Chapter)

573

Radiator electric cooling fan relay 
and/or circuit

Carry out system test (see below)

574

Radiator (high-speed) electric 
cooling fan relay and/or circuit

Carry out system test (see below)

575

Fuel pump and/or fuel cut-off 
switch circuits

Carry out system test (see below)

576, 577

Accelerator pedal not depressed fully during 
test procedure - automatic transmission 
kickdown not activated

Repeat test

621

Automatic transmission shift solenoid 1 circuit

Refer to Chapter 7, Part B

622

Automatic transmission shift solenoid 2 circuit

Refer to Chapter 7, Part B

624

Automatic transmission electronic 
pressure control solenoid

Refer to Chapter 7, Part B

625

Automatic transmission electronic 
pressure control solenoid circuit

Refer to Chapter 7, Part B

629

Automatic transmission torque 
converter clutch solenoid

Refer to Chapter 7, Part B

634

Selector lever position sensor  circuit

Check component (Chapter 7, Part B)

635, 637

Automatic transmission fluid temperature sensor Refer to Chapter 7, Part B

639

Automatic transmission speed sensor

Refer to Chapter 7, Part B

645

Automatic transmission 1st speed

Refer to Chapter 7, Part B

646

Automatic transmission 2nd speed

Refer to Chapter 7, Part B

647

Automatic transmission 3rd speed

Refer to Chapter 7, Part B

648

Automatic transmission 4th speed

Refer to Chapter 7, Part B

653

Automatic transmission overdrive 
cancel button and “Economy/Sport” 
mode switch not operated during test

Repeat test

998

Warning code

Check fault(s) indicated by subsequent code(s)

Emissions control systems  6•9

6

Ignition timing and base idle
speed check

Note: The following procedure is a check only,
essentially of the ECU. Both the ignition timing
and the base idle speed are controlled by the
ECU. The ignition timing is not adjustable at
all; the base idle speed is set in production,
and should not be altered.
38 If the fault code read-out (with any checks
resulting from it) has not eliminated the fault,
the next step is to check the ECU’s control of
the ignition timing and the base idle speed.
This task requires the use of a Ford STAR
tester (a proprietary fault code reader can be
used only if it is capable of inducing the ECU
to enter its “Service Adjustment Programme”),
coupled with an accurate tachometer and a
good-quality timing light. Without this
equipment, the task is not possible; the
vehicle must be taken to a Ford dealer for
attention.
39 To make the check, apply the handbrake,
switch off the air conditioning (where fitted)
and any other electrical loads (lights, heated
rear window, etc), then select neutral (manual
transmission) or the “P” position (automatic
transmission). Start the engine, and warm it
up to normal operating temperature. The
radiator electric cooling fan must be running
continuously while the check is made; this
should be activated by the ECU, when
prompted by the tester. Switch off the engine,
and connect the test equipment as directed
by the manufacturer - refer to paragraph 26
above for details of STAR tester connection.
40 Raise and support the front of the vehicle
securely, and remove the auxiliary drivebelt
cover (see Chapter 1). Emphasise the two
pairs of notches in the inner and outer rims of
the crankshaft pulley, using white paint. Note
that an ignition timing reference mark is not
provided on the pulley - in the normal
direction of crankshaft rotation (clockwise,
seen from the right-hand side of the vehicle)
the first pair of notches are irrelevant to the
vehicles covered in this manual, while the
second pair indicate Top Dead Centre (TDC)
when aligned with the rear edge of the raised
mark on the sump; when checking the ignition
timing, therefore, the (rear edge of the) sump

mark should appear just before the TDC
notches (see Part A of Chapter 2, Section 4,
for further information if required).
41 Start the engine and allow it to idle. Work
through the engine-running test procedure
until the ECU enters its “Service Adjustment
Programme” - see paragraph 35 above.
42 Use the timing light to check that the
timing marks appear approximately as
outlined above at idle speed. Do not spend
too much time on this check; if the timing
appears to be incorrect, the system may have
a fault, and a full system test must be carried
out (see below) to establish its cause.
43 Using the tachometer, check that the
base idle speed is as given in the
Specifications Section of Chapter 4.
44 If the recorded speed differs significantly
from the specified value, check for air leaks,
as described in the preliminary checks
(paragraphs 15 to 18 above), or any other
faults which might cause the discrepancy.
45 The base idle speed is set in production
by means of an air bypass screw (located in
the front right-hand corner of the throttle
housing) which controls the amount of air that
is allowed to pass through a bypass passage,
past the throttle valve when it is fully closed in
the idle position; the screw is then sealed with
a white tamperproof plug (see illustration). In
service, the idle speed is controlled by the
ECU, which has the ability to compensate for
engine wear, build-up of dirt in the throttle
housing, and other factors which might
require changes in idle speed. The air bypass
screw setting should not, therefore, be
altered. If any alterations are made, a blue
tamperproof plug must be fitted, and the
engine should be allowed to idle for at least
five minutes on completion, so that the ECU
can re-learn its idle values.
46 When both checks have been made and
the “Service Adjustment Programme” is
completed, follow the tester manuals to
return to the fault code read-out, and
establish whether the fault has been cured or
not.

Basic check of ignition system

47 If the checks so far have not eliminated
the fault, the next step is to carry out a basic
check of the ignition system components,
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.

Basic check of fuel system

48 If the checks so far have not eliminated
the fault, the next step is to carry out a basic
check of the fuel system components.
49 Assuming that the preliminary checks
have established that the fuel pump is
operating correctly, that the fuel filter is

unlikely to be blocked, and also that there are
no leaks in the system, the next step is to
check the fuel pressure (see Chapter 4). If this
is correct, check the injectors (see Chapter 4)
and the Positive Crankcase Ventilation system
(see Chapter 1).

System test

50 The final element of the Ford testing
procedure is to carry out a system test, using
a break-out box - this is a device that is
connected between the ECU and its electrical
connector, so that the individual circuits
indicated by the fault code read-out can be
tested while connected to the system, if
necessary with the engine running. In the case
of many of the system’s components, this
enables their output voltages to be measured
- a more accurate means of testing.
51 In addition to the break-out box and the
adaptors required to connect it, several items
of specialist equipment are needed to
complete these tests. This puts them quite
beyond the scope of many smaller dealers, let
alone the DIY owner; the vehicle should be
taken to a Ford dealer for attention.

Note: This Section is concerned principally
with the sensors which give the ECU the
information it needs to control the various
engine management sub-systems - for further
details of those systems and their other
components, refer to the relevant Chapter of
this manual.

General

ECU (Electronic Control Unit)

1 This component is the heart of the entire
engine management system, controlling the
fuel injection, ignition and emissions control
systems. It also controls sub-systems such as
the radiator cooling fan, air conditioning and
automatic transmission, where appropriate.
Refer to Section 2 of this Chapter for an
illustration of how it works.

Air mass meter

2 This uses a “hot-wire” system, sending the
ECU a constantly-varying (analogue) voltage
signal corresponding to the mass of air
passing into the engine. Since air mass varies
with temperature (cold air being denser than
warm), measuring air mass provides the ECU
with a very accurate means of determining the
correct amount of fuel required to achieve the
ideal air/fuel mixture ratio.

Crankshaft speed/position sensor

3 This is an inductive pulse generator bolted
(in a separate bracket) to the cylinder
block/crankcase, to scan the ridges between
36 holes machined in the inboard (right-hand)
face of the flywheel/driveplate. As each ridge

4 Information sensors - 

general information, testing,
removal and refitting

6•10 Emissions control systems

3.45  Throttle housing air bypass screw is

sealed on production with a white

tamperproof plug (arrowed)

passes the sensor tip, a signal is generated,
which is used by the ECU to determine engine
speed.
4 The ridge between the 35th and 36th holes
(corresponding to 90° BTDC) is missing - this
step in the incoming signals is used by the
ECU to determine crankshaft (ie, piston)
position.

Camshaft position sensor

5 This is bolted to the rear left-hand end of
the cylinder head, to register with a lobe on
the inlet camshaft. It functions in the same
way as the crankshaft speed/position sensor,
producing a series of pulses (corresponding
to No 1 cylinder at 46° ATDC); this gives the
ECU a reference point, to enable it to
determine the firing order, and operate the
injectors in the appropriate sequence.

Coolant temperature sensor

6 This component, which is screwed into the
top of the thermostat housing, is an NTC
(Negative Temperature Coefficient) thermistor
- that is, a semi-conductor whose electrical
resistance decreases as its temperature
increases. It provides the ECU with a
constantly-varying (analogue) voltage signal,
corresponding to the temperature of the
engine coolant. This is used to refine the
calculations made by the ECU, when
determining the correct amount of fuel
required to achieve the ideal air/fuel mixture
ratio.

Intake air temperature sensor

7 This component, which is screwed into the
underside of the air intake resonator, is also an
NTC thermistor - see the previous paragraph -
providing the ECU with a signal corresponding
to the temperature of air passing into the
engine. This is used to refine the calculations
made by the ECU, when determining the
correct amount of fuel required to achieve the
ideal air/fuel mixture ratio.

Throttle potentiometer

8 This is mounted on the end of the throttle
valve spindle, to provide the ECU with a
constantly-varying (analogue) voltage signal
corresponding to the throttle opening. This
allows the ECU to register the driver’s input
when determining the amount of fuel required
by the engine.

Vehicle speed sensor

9 This component is a Hall-effect generator,
mounted on the transmission’s speedometer
drive. It supplies the ECU with a series of
pulses corresponding to the vehicle’s road
speed, enabling the ECU to control features
such as the fuel shut-off on the overrun, and
to provide information for the trip computer,
adaptive damping and cruise control systems
(where fitted).

Power steering pressure switch

10 This is a pressure-operated switch,
screwed into the power steering system’s

high-pressure pipe. Its contacts are normally
closed, opening when the system reaches the
specified pressure - on receiving this signal,
the ECU increases the idle speed, to
compensate for the additional load on the
engine.

Exhaust gas pressure differential
sensor

11 This component measures the difference
in pressure of the exhaust gases across a
venturi (restriction) in the Exhaust Gas
Recirculation (EGR) system’s pipe, and sends
the ECU a voltage signal corresponding to the
pressure difference.

Oxygen sensor

12 The oxygen sensor in the exhaust system
provides the ECU with constant feedback -
“closed-loop” control - which enables it to
adjust the mixture to provide the best possible
conditions for the catalytic converter to
operate.
13 The sensor has a built-in heating element
which is controlled by the ECU, in order to
bring the sensor’s tip to an efficient operating
temperature as rapidly as possible. The
sensor’s tip is sensitive to oxygen, and sends
the ECU a varying voltage depending on the
amount of oxygen in the exhaust gases. If the
intake air/fuel mixture is too rich, the exhaust
gases are low in oxygen, so the sensor sends
a low-voltage signal, the voltage rising as the
mixture weakens and the amount of oxygen in
the exhaust gases rises. Peak conversion
efficiency of all major pollutants occurs if the
intake air/fuel mixture is maintained at the
chemically-correct ratio for the complete
combustion of petrol, of 14.7 parts (by weight)
of air to 1 part of fuel (the “stoichiometric”
ratio). The sensor output voltage alters sharply
around this point, the ECU using the signal
change as a reference point, and correcting
the air/fuel mixture by altering the fuel injector
pulse width.

Air conditioning system

14 Two pressure-operated switches and the
compressor clutch solenoid are connected to
the ECU, to enable it to determine how the
system is operating. The ECU can increase
idle speed or switch off the system, as
necessary, so that normal vehicle operation
and driveability are not impaired. See Chapter
3 for further details, but note that diagnosis
and repair should be left to a dealer service
department or air conditioning specialist.

Automatic transmission

15 In addition to the driver’s controls, the
transmission has a speed sensor, a fluid
temperature sensor (built into the solenoid
valve unit), and a selector lever position
sensor. All of these are connected to the ECU,
to enable it to control the transmission
through the solenoid valve unit. See Part B of
Chapter 7 for further details.

Testing

ECU (Electronic Control Unit)

16 Do not attempt to “test” the ECU with any
kind of equipment. If it is thought to be faulty,
take the vehicle to a Ford dealer for the entire
electronic control system to be checked using
the proper diagnostic equipment. Only if all
other possibilities have been eliminated should
the ECU be considered at fault, and replaced.

Air mass meter

17 Testing of this component is beyond the
scope of the DIY mechanic, and should be left
to a Ford dealer.

Crankshaft speed/position sensor

18 Unplug the electrical connector from the
sensor.
19 Using an ohmmeter, measure the
resistance between the sensor terminals.
Compare this reading to the one listed in the
Specifications Section at the beginning of this
Chapter. If the indicated resistance is not
within the specified range, renew the sensor.
20 Plug in the sensor’s electrical connector
on completion.

Camshaft position sensor

21 The procedure is as described in
paragraphs 18 to 20 above.

Coolant temperature sensor

22 Refer to Chapter 3.

Intake air temperature sensor

23 Unplug the electrical connector from the
sensor.
24 Using an ohmmeter, measure the
resistance between the sensor terminals.
Depending on the temperature of the sensor
tip, the resistance measured will vary, but it
should be within the broad limits given in the
Specifications Section of this Chapter. If the
sensor’s temperature is varied - by placing it
in a freezer for a while, or by warming it gently
- its resistance should alter accordingly.
25 If the results obtained show the sensor to
be faulty, renew it.

Throttle potentiometer

26 Remove the plenum chamber (see
Chapter 4) and unplug the potentiometer’s
electrical connector.
27 Using an ohmmeter, measure the
resistance between the unit’s terminals - first
between the centre terminal and one of the
outer two, then from the centre to the
remaining outer terminal. The resistance
should be within the limits given in the
Specifications Section of this Chapter, and
should alter smoothly as the throttle valve is
moved from the fully-closed (idle speed)
position to fully open and back again.
28 If the resistance measured is significantly
different from the specified value, if there are
any breaks in continuity, or if the reading
fluctuates erratically as the throttle is
operated, the potentiometer is faulty, and
must be renewed.

Emissions control systems  6•11

6

Vehicle speed sensor

29 Testing of this component is beyond the
scope of the DIY mechanic, and should be left
to a Ford dealer.

Power steering pressure switch

30 Unplug the electrical connector from the
sensor.
31 Using an ohmmeter, measure the
resistance between the switch terminals. With
the engine switched off, or idling with the
roadwheels in the straight-ahead position,
little or no resistance should be measured.
With the engine running and the steering on
full-lock, the pressure increase in the system
should open the switch contacts, so that
infinite resistance is now measured.
32 If the results obtained show the switch to
be faulty, renew it.

Exhaust gas pressure differential
sensor

33 Testing of this component is beyond the
scope of the DIY mechanic, and should be left
to a Ford dealer.

Oxygen sensor

34 Testing of this component can be done
only by attaching special diagnostic
equipment to the sensor wiring, and checking
that the voltage varies from low to high values
when the engine is running; do not attempt to
“test” any part of the system with anything
other than the correct test equipment. This is
beyond the scope of the DIY mechanic, and
should be left to a Ford dealer.

Removal and refitting

General

35 Before disconnecting any of these
components, always disconnect the power by
uncoupling the battery terminals, negative
(earth) lead first - see Section 1 of Chapter 5.

ECU (Electronic Control Unit)

Note: The ECU is fragile. Take care not to
drop it or subject it to any other kind of
impact, and do not subject it to extremes of
temperature, or allow it to get wet.
36 Carefully prise the power steering fluid
reservoir upwards out of its clip on the
suspension mounting. Unscrew the ECU
connector’s retaining bolt, and unplug the
connector (see illustrations).
37 Working in the passenger compartment,
unscrew the retaining bolt and withdraw the
mounting bracket (see illustration).
38 Lifting the ECU to release it from the
bulkhead carrier bracket, withdraw the unit
(see illustration).
39 Refitting is the reverse of the removal
procedure. Whenever the ECU (or battery) is
disconnected, the information relating to idle
speed control and other operating values will
be lost from its memory until the unit has re-
programmed itself; until then, there may be
surging, hesitation, erratic idle and a
generally-inferior level of performance. To
allow the ECU to re-learn these values, start
the engine and run it as close to idle speed as
possible until it reaches its normal operating

temperature, then run it for approximately two
minutes at 1200 rpm. Next, drive the vehicle
as far as necessary - approximately 5 miles of
varied driving conditions is usually sufficient -
to complete the re-learning process.

Air mass meter

40 Releasing its wire clip, unplug the meter’s
electrical connector (see illustration).
41 Release the clips and lift the air cleaner
cover, then release the two smaller clips and
detach the meter from the cover (see
illustration).
42 Slacken the clamp securing the meter to
the resonator hose, and withdraw the meter.
43 Refitting is the reverse of the removal
procedure. Ensure that the meter and air
cleaner cover are seated correctly and securely
fastened, so that there are no air leaks.

Crankshaft speed/position sensor

44 Refer to Chapter 5.

Camshaft position sensor

45 Remove the air mass meter and resonator
(refer to Chapter 4) to gain access to the
sensor (see illustration). Release the fuel
feed and return hoses from their clip.
46 Releasing its wire clip, unplug the
sensor’s electrical connector. Remove the
retaining screw, and withdraw the sensor from
the cylinder head; be prepared for slight oil
loss.
47 Refitting is the reverse of the removal
procedure, noting the following points:

6•12 Emissions control systems

4.36A  Unclip and lift power steering fluid

reservoir - take care not to spill fluid . . .

4.36B  . . . unscrew bolt (arrowed) to

release ECU’s electrical connector

4.37  Unscrew retaining bolt and withdraw

ECU’s mounting bracket . . .

4.40  Unplugging the air mass meter’s

electrical connector . . .

4.38  . . . then lift ECU to disengage it, and

withdraw it

4.41  . . . release clips to separate meter

from air cleaner cover