Chapter 6 Engine Management And Emission Control Systems

6 1Chapter 6Engine management and emission control systemsContentsCatalytic converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Electronic Control Unit (ECU) - removal and refitting . . . . . . . . . . . . 3Evaporative emissions control (EVAP) system . . . . . . . . . . . . . . . . . 6Evaporative emissions control system inspection . . .See Chapter 1General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Information sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Motronic engine management system self-diagnosis general information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Positive crankcase ventilation (PCV) system . . . . . . . . . . . . . . . . . . 5Degrees of difficultyEasy, suitable fornovice with littleexperienceFairly easy, suitablefor beginner withsome experience1 General informationTo prevent pollution of the atmospherefrom incomplete combustion or evaporationof the fuel, and to maintain good driveabilityand fuel economy, a number of emissioncontrol systems are used on these vehicles.Not all of these systems are fitted to allmodels, but they include the following:Catalytic converterEvaporative emission control (EVAP) systemPositive crankcase ventilation (PCV) systemElectronic engine managementThe Sections in this Chapter includegeneraldescriptionsandcheckingprocedures within the scope of the homemechanic, as well as component renewalprocedures (when possible) for each of thesystems listed above.Before assuming that an emissions controlsystem is malfunctioning, check the fuel andignition systems carefully. The diagnosis ofsome emission control devices requiresspecialised tools, equipment and training. Ifchecking and servicing become too difficult,or if a procedure is beyond your ability,consult a dealer service department or otherspecialist.The most frequent cause ofemission system problems issimply a leaking vacuum hoseor loose wire, so alwayscheck the hose and wiring connectionsfirst.Fairly difficult,suitable for competentDIY mechanicDifficult, suitable forexperienced DIYmechanicThis doesn’t mean, however, that emissioncontrol systems are particularly difficult tomaintain and repair. You can quickly andeasily perform many checks, and do most ofthe regular maintenance at home withcommon tune-up and hand tools.Pay close attention to any specialprecautions outlined in this Chapter. It shouldbe noted that the illustrations of the varioussystems may not exactly match the systemfitted on your vehicle because ofchanges made by the manufacturer duringproduction.2 Motronic engine managementsystem self-diagnosis general informationThe Motronic engine management systemcontrol unit (computer) has a built-in selfdiagnosis system, which detects malfunctionsin the system sensors and stores them asfault codes in its memory. It is not possiblewithout dedicated test equipment to extractthese fault codes from the control unit.However, the procedures given in Chapters 4and 5 may be used to check individualcomponents and sensors of the Motronicsystem. If this fails to pinpoint a fault, then thevehicle should be taken to a BMW dealer, whowill have the necessary diagnosticequipment to call up the fault codes from thecontrol unit. You will then have theoption to repair the fault yourself, oralternatively have the fault repaired by theBMW dealer.Very difficult,suitable for expertDIY or professional3 Electronic control unit (ECU)- removal and refitting2Removal1 The Electronic Control Unit (ECU) is locatedeither inside the passenger compartmentunder the right-hand side of the facia panel on3-Series models, or in the enginecompartment on the right-hand side on 5Series models (see Chapter 4).2 Disconnect the battery negative cable.Caution: If the radio in yourvehicle is equipped with an antitheft system, make sure youhave the correct activation codebefore disconnecting the battery. Refer tothe information on page 0-7 at the front ofthis manual before detaching the cable.Note: If, after connecting the battery, thewrong language appears on the instrumentpanel display, refer to page 0-7 for thelanguage resetting procedure.3 First remove the access cover on modelswith the ECU on the right-hand side of theengine compartment (see Chapter 4).4 If the ECU is located inside the vehicle,remove the access cover on the right-hand side.5 Unplug the electrical connectors from theECU.6 Remove the retaining bolts from the ECUbracket.7 Carefully remove the ECU. Note: Avoid staticelectricity damage to the ECU by wearing rubbergloves, and do not touch the connector pins.Refitting8 Refitting is a reversal of removal.6

6 2 Engine management and emission control systems4.1 The coolant temperature sensor(arrowed) is usually located next to thetemperature sender unit, near the fuelpressure regulator4 Information sensors2Note: Refer to Chapters 4 and 5 for additionalinformation on the location and diagnosis ofthe information sensors that are not covered inthis Section.Coolant temperature sensor4.2 Check the resistance of the coolanttemperature sensor at differenttemperatures4.6 The oxygen sensor (arrowed) is usuallylocated in the exhaust pipe, downstreamfrom the exhaust manifoldCaution: Handle the coolantsensor with care. Damage to thissensor will affect the operation ofthe entire fuel injection system.Note: It may be necessary to drain a smallamount of coolant from the radiator beforeremoving the sensor.4 Before the sensor is fitted, ensure itsthreads are clean, and apply a little sealant tothem.5 Refitting is the reverse of removal.0.45 volts at 1500 rpm or greater, the ECUfault code memory will be activated.9 When there is a problem with the oxygensensor or its circuit, the ECU operates in the“open-loop” mode - that is, it controls fueldelivery in accordance with a programmeddefault value instead of with feedbackinformation from the oxygen sensor.10 The proper operation of the oxygensensor depends on four conditions:a) Electrical - The low voltages generated bythe sensor depend upon good, cleanconnections, which should be checkedwhenever a malfunction of the sensor issuspected or indicated.b) Outside air supply - The sensor isdesigned to allow air circulation to theinternal portion of the sensor. Wheneverthe sensor is disturbed, make sure the airpassages are not restricted.c) Proper operating temperature - The ECUwill not react to the sensor signal until thesensor reaches approximately 320º C.This factor must be taken intoconsideration when evaluating theperformance of the sensor.d) Unleaded fuel - The use of unleaded fuelis essential for proper operation of thesensor. Make sure the fuel you are usingis of this type.11 In addition to observing the aboveconditions, special care must be takenwhenever the sensor is serviced.a) The oxygen sensor has a permanentlyattached pigtail and electrical connector,which should not be removed from thesensor. Damage or removal of the pigtailor electrical connector can adverselyaffect operation of the sensor.b) Grease, dirt and other contaminantsshould be kept away from the electricalconnector and the louvered end of thesensor.c) Do not use cleaning solvents of any kindon the oxygen sensor.d) Do not drop or roughly handle the sensor.e) The silicone boot must be fitted in thecorrect position, to prevent the boot frombeing melted and to allow the sensor tooperate properly.Oxygen sensorGeneral descriptionGeneral description1 The coolant temperature sensor (seeillustration) is a thermistor (a resistor whichvaries its resistance value in accordance withtemperature changes). The change in theresistance value regulates the amount ofvoltage that can pass through the sensor. Atlow temperatures, the sensor’s resistance ishigh. As the sensor temperature increases, itsresistance will decrease. Any failure in thissensor circuit will in most cases be due to aloose or shorted-out wire; if no wiringproblems are evident, check the sensor asdescribed below.Note: Oxygen sensors are normally only fittedto those vehicles equipped with a catalyticconverter. Most oxygen sensors are located inthe exhaust pipe, downstream from theexhaust manifold. On 535 models, the oxygensensor is mounted in the catalytic converter.The sensor’s electrical connector is locatednear the bulkhead (left side) for easy access.6 The oxygen sensor, which is located in theexhaust system (see illustration), monitorsthe oxygen content of the exhaust gas. Theoxygen content in the exhaust reacts with theoxygen sensor, to produce a voltage outputwhich varies from 0.1 volts (high oxygen, leanmixture) to 0.9 volts (low oxygen, richmixture). The ECU constantly monitors thisvariable voltage output to determine the ratioof oxygen to fuel in the mixture. The ECUalters the air/fuel mixture ratio by controllingthe pulse width (open time) of the fuelinjectors. A mixture ratio of 14.7 parts air to 1part fuel is the ideal mixture ratio forminimising exhaust emissions, thus allowingthe catalytic converter to operate at maximumefficiency. It is this ratio of 14.7 to 1 which theECU and the oxygen sensor attempt tomaintain at all times.7 The oxygen sensor produces no voltagewhen it is below its normal operatingtemperature of about 320º C. During this initialperiod before warm-up, the ECU operates in“open-loop” mode (ie without the informationfrom the sensor).8 If the engine reaches normal operatingtemperature and/or has been running for twoor more minutes, and if the oxygen sensor isproducing a steady signal voltage belowCheck2 To check the sensor, first check itsresistance (see illustration) when it iscompletely cold (typically 2100 to 2900 ohms).Next, start the engine and warm it up until itreaches operating temperature. The resistanceshould be lower (typically 270 to 400 ohms).Note: If restricted access to the coolanttemperature sensor makes it difficult to attachelectrical probes to the terminals, remove thesensor as described below, and perform thetests in a container of heated water to simulatethe conditions.Warning: Wait until the engine iscompletely cool before beginningthis procedure.Renewal3 To remove the sensor, depress the springlock, unplug the electrical connector, thencarefully unscrew the sensor. Be prepared forsome coolant spillage; to reduce this, havethe new sensor ready for fitting as quickly aspossible.