All about Ford Mondeo

Information sensors - general information, testing,removal and refitting
Emissions control systems / Information sensors - general information, testing,removal and refitting


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 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 drivers 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 transmissions speedometer drive. It supplies the ECU with a series of pulses corresponding to the vehicles 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 systems 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) systems 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 sensors tip to an efficient operating temperature as rapidly as possible. The sensors 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 drivers 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 sensors 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 sensors 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 potentiometers electrical connector.

27 Using an ohmmeter, measure the resistance between the units 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.

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 connectors retaining bolt, and unplug the connector (see illustrations).

4.36A Unclip and lift power steering fluid reservoir - take care not to spill
4.36A Unclip and lift power steering fluid reservoir - take care not to spill fluid . . .

4.36B . . . unscrew bolt (arrowed) to release ECUs electrical connector
4.36B . . . unscrew bolt (arrowed) to release ECUs electrical connector

37 Working in the passenger compartment, unscrew the retaining bolt and withdraw the mounting bracket (see illustration).

4.37 Unscrew retaining bolt and withdraw ECUs mounting bracket . . .
4.37 Unscrew retaining bolt and withdraw ECUs mounting bracket . . .

38 Lifting the ECU to release it from the bulkhead carrier bracket, withdraw the unit (see illustration).

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

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 reprogrammed 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 meters electrical connector (see illustration).

4.40 Unplugging the air mass meters electrical connector . . .
4.40 Unplugging the air mass meters electrical connector . . .

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).

4.41 . . . release clips to separate meter from air cleaner cover
4.41 . . . release clips to separate meter from air cleaner cover

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.

4.45 Camshaft position sensor is located at left-hand rear end of cylinder
4.45 Camshaft position sensor is located at left-hand rear end of cylinder head

46 Releasing its wire clip, unplug the sensors 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: (a) Apply petroleum jelly or clean engine oil to the sensors sealing O-ring.

(b) Locate the sensor fully in the cylinder head, and wipe off any surplus lubricant before securing it.

(c) Tighten the screw to the specified torque wrench setting.

Coolant temperature sensor 48 Refer to Chapter 3, Section 6.

Intake air temperature sensor 49 Remove the air mass meter and resonator (refer to Chapter 4) to gain access to the sensor (see illustration).

4.49 Intake air temperature sensor (arrowed) is screwed into underside of air
4.49 Intake air temperature sensor (arrowed) is screwed into underside of air intake resonator

50 Releasing its clip, unplug the sensors electrical connector, then unscrew the sensor from the resonator.

51 Refitting is the reverse of the removal procedure. Tighten the sensor to the specified torque wrench setting; if it is overtightened, its tapered thread may crack the resonator.

Throttle potentiometer
52 Remove the plenum chamber (see Chapter 4). Releasing its wire clip, unplug the large electrical connector (next to the fuel pressure regulator).

53 Releasing its wire clip, unplug the potentiometers electrical connector. Remove the retaining screws, and withdraw the unit from the throttle housing (see illustration). Do not force the sensors centre to rotate past its normal operating sweep; the unit will be seriously damaged.

4.53 Throttle potentiometer is secured by two screws (arrowed)
4.53 Throttle potentiometer is secured by two screws (arrowed)

54 Refitting is the reverse of the removal procedure, noting the following points: (a) Ensure that the potentiometer is correctly orientated, by locating its centre on the Dshaped throttle shaft (throttle closed), and aligning the potentiometer body so that the bolts pass easily into the throttle housing.

(b) Tighten the screws evenly and securely (but do not overtighten them, or the potentiometer body will be cracked).

Vehicle speed sensor
55 The sensor is mounted at the base of the speedometer drive cable, and is removed with the speedometer drive pinion (see illustration). Refer to the relevant Section of Chapter 7, Part A or B, as applicable.

Power steering pressure switch

4.55 Vehicle speed sensor A, with its electrical connector B
4.55 Vehicle speed sensor A, with its electrical connector B

56 Releasing its clip, unplug the switchs electrical connector, then unscrew the switch (see illustration). Place a wad of rag underneath, to catch any spilt fluid. If a sealing washer is fitted, renew it if it is worn or damaged.

4.56 Power steering pressure switch is screwed into pipe at right-hand rear
4.56 Power steering pressure switch is screwed into pipe at right-hand rear end of engine

57 Refitting is the reverse of the removal procedure; tighten the switch securely, then top-up the fluid reservoir (see Chapter 1) to replace any fluid lost from the system, and bleed out any trapped air (see Chapter 10, Section 33).

Exhaust gas pressure differential sensor
Note: See also Section 6, illustration 6.21.

58 If better access is required, remove the resonator (see Chapter 4).

59 Releasing its wire clip, unplug the sensors electrical connector. Remove the two retaining screws, withdraw the unit from the bulkhead mounting bracket, then disconnect the two vacuum hoses. Note that the hoses are of different sizes, to ensure that they cannot be mixed up on reconnection.

60 Check the condition of both hoses, and renew them if necessary (see Chapter 1).

61 Refitting is the reverse of the removal procedure. Ensure that the hoses are securely connected to the correct unions.

Oxygen sensor
Note: The sensor is delicate, and will not work if it is dropped or knocked, if its power supply is disrupted, or if any cleaning materials are used on it.

62 Release the sensors electrical connector from its bracket on the engine/transmission front mounting, and unplug it to disconnect the sensor (see illustration).

4.62 Oxygen sensor is screwed into exhaust system front downpipe . . .
4.62 Oxygen sensor is screwed into exhaust system front downpipe . . .

63 Raising and supporting the front of the vehicle if required to remove the sensor from underneath, unscrew the sensor from the exhaust system front downpipe; collect the sealing washer (where fitted).

64 On refitting, clean the sealing washer (where fitted) and renew it if it is damaged or worn. Apply a smear of anti-seize compound to the sensors threads, to prevent them from welding themselves to the downpipe in service. Refit the sensor, tightening it to its specified torque wrench setting; a slotted socket will be required to do this (see illustration). Reconnect the wiring and refit the connector plug.

4.64 . . . slotted socket will be required to tighten sensor with a torque
4.64 . . . slotted socket will be required to tighten sensor with a torque wrench


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