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.
Engine management and emission control systems 6 323 Refit the sensor and tighten it securely.24 Reconnect the electrical connector of thepigtail lead to the main engine wiring harness.25 Lower the vehicle, and reconnect thebattery.OxygenSensorHeated powersensor type output signal supply (12V)Unheated(single-wire)4.12a The oxygen sensor, once it iswarmed up (320º C), puts out a very smallvoltage signal. To verify it is working,check for voltage with a digital voltmeter(the voltage signals usually range from0.1 to 1.0 volt)Check12 Warm up the engine, and let it run at idle.Disconnect the oxygen sensor electricalconnector, and connect the positive probe ofa voltmeter to the oxygen sensor outputconnector terminal (refer to the followingtable) and the negative probe to earth (seeillustrations).Note: Most oxygen sensor electricalconnectors are located at the rear of theengine, near the bulkhead. Look for a largerubber boot attached to a thick wire harness.On early 535i models, the connector for theoxygen sensor heater circuit is under thevehicle. Look for a small protective cover.These models should have the updatedoxygen sensor fitted, to make access similarto other models. Consult your dealer servicedepartment for additional information.13 Increase and then decrease the enginespeed, and monitor the voltage.14 When the speed is increased, the voltageshould increase to 0.5 to 1.0 volts. When thespeed is decreased, the voltage should fall toabout 0 to 0.4 volts.15 Also where applicable, inspect the oxygensensor heater (models with multi-wiresensors). With the ignition on, disconnect theoxygen sensor electrical connector, andconnect a voltmeter across the terminalsdesignated in the chart (see below). Thereshould be battery voltage (approximately12 volts).16 If the reading is not correct, check theoxygen sensor heater relay (see Chapter 12).If the information is not available, check theowner’s handbook for the exact location ofthe oxygen sensor heater relay. The relayshould receive battery voltage.17 If the oxygen sensor fails any of thesetests, renew it.4.12b These oxygen sensor terminaldesignations are for the harness side only.Use the corresponding terminals on thesensor side for the testing procedures(there are three different four-wire oxygensensor connectors available - don’t getthem mixed up)(assuming you are planning to re-use it inanother manifold or pipe), start and run theengine for a minute or two, then switch it off.Be careful not to burn yourself during thefollowing procedure.18 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.19 Raise and support the vehicle.20 Disconnect the electrical connector fromthe sensor.21 Carefully unscrew the sensor.Caution: Excessive force maydamage the threads.22 A high-temperature anti-seize compoundmust be used on the threads of the sensor, tofacilitate future removal. The threads of newsensors will already be coated with thiscompound, but if an old sensor is removedand refitted, recoat the threads.black wire ( )Not applicableHeated(three-wire)terminal 1 ( )terminals3 ( ) and 2 (-)Heated(four-wire)terminal 2 ( )terminals4 ( ) and 3 (-)Throttle Position Sensor (TPS)General description26 The Throttle Position Sensor (TPS) islocated on the end of the throttle shaft on thethrottle body. By monitoring the outputvoltage from the TPS, the ECU can determinefuel delivery based on throttle valve angle(driver demand). In this system, the TPS actsas a switch rather than a potentiometer. Oneset of throttle valve switch contacts is closed(continuity) only at idle. A second set ofcontacts closes as the engine approachesfull-throttle. Both sets of contacts are open(no continuity) between these positions. Abroken or loose TPS can cause intermittentbursts of fuel from the injector and anunstable idle, because the ECU thinks thethrottle is moving.27 All models (except for early 535i modelswith automatic transmission) combine the idleand full-throttle switch; a separate idleposition switch indicates the closed-throttleposition, while the TPS is used for the fullthrottle position. On 535i models withautomatic transmission, the TPS is connecteddirectly to the automatic transmission controlunit. With the throttle fully open, thetransmission control unit sends the fullthrottle signal to the Motronic control unit.All models except early 535i withautomatic transmissionCheck28 Remove the electrical connector from theTPS, and connect an ohmmeter to terminals 2and 18 (see illustrations). Open the throttleRenewalNote: Because it is fitted in the exhaustmanifold, converter or pipe, which contractswhen cool, the oxygen sensor may be verydifficult to loosen when the engine is cold.Rather than risk damage to the sensor4.28a The TPS on L-Jetronic systems islocated under the intake manifold(terminals arrowed)4.28b First check for continuity betweenterminals 2 and 18 with the throttle closed(later Motronic system shown) . . .6
6 4 Engine management and emission control systems4.28c . . . then check for continuitybetween terminals 3 and 18 as the throttleis openedslightly by hand. Release the throttle slowlyuntil it reaches 0.2 to 0.6 mm from the throttlestop. There should be continuity.29 Check the resistance between terminals 3and 18 as the throttle is opened. There shouldbe continuity when the throttle switch is within8 to 12 degrees of fully-open. If the readingsare incorrect, adjust the TPS.30 If all the resistance readings are correctand the TPS is properly adjusted, check forpower (5 volts) at the sensor, and if necessarytrace any wiring circuit problems between thesensor and ECU (see Chapter 12).Adjustment31 If the adjustment is not as specified(paragraphs 28 to 30), loosen the screws onthe TPS, and rotate the sensor into the correctadjustment. Follow the procedure forchecking the TPS given above, and tightenthe screws when the setting is correct.32 Recheck the TPS once more; if thereadings are correct, reconnect the TPSharness connector.connect an ohmmeter to terminals 1 and 2.There should be continuity. Open the throttleslightly, and measure the resistance. Thereshould now be no continuity.35 Check for the correct voltage signals fromthe TPS, with the throttle closed and theignition on. Probe the back of the TPSconnector with a voltmeter, and check forvoltage at terminal 3 (black wire) and earth.There should be 5 volts present. Also, probeterminal 3 (black wire) and terminal 1 (brownwire). There should be 5 volts present herealso.36 Check for voltage at terminal 2 (yellowwire) and terminal 1 (brown wire), and slowlyopen the throttle. The voltage should increasesteadily from 0.7 volts (throttle closed) to4.8 volts (throttle fully-open).Adjustment37 First measure the stabilised voltage. Withthe ignition on and the throttle closed,measure the voltage between terminal 3(black wire) and terminal 1 (brown wire). Itshould be about 5 volts.38 Next, loosen the sensor mounting screws,and connect the voltmeter to terminal 2(yellow wire) and terminal 3 (black wire). Withthe throttle fully open, rotate the switch untilthere is 0.20 to 0.24 volts less than thestabilised voltage. Note: You will need adigital voltmeter to measure these smallchanges in voltage.39 Recheck the TPS once more; if thereadings are correct, reconnect the TPSelectrical connector. It is a good idea to lockthe TPS screws with paint or thread-lockingcompound.Early 535i models with automatictransmissionGeneral description40 The airflow meter is located on the airintake duct. The airflow meter measures theamount of air entering the engine. The ECUuses this information to control fuel delivery. Alarge volume of air indicates acceleration,while a small volume of air indicatesdeceleration or idle. Refer to Chapter 4 for allthe diagnostic checks and renewalprocedures for the airflow meter.Ignition timing sensors41 Ignition timing is electronically-controlledon Motronic systems, and is not adjustable.During starting, a crankshaft position sensorrelays the crankshaft position to the ECU, andan initial baseline ignition point is determined.Once the engine is running, the ignition pointis continually changing based on the variousinput signals to the ECU. Engine speed issignalled by a speed sensor. Early Motronicsystems have the reference sensor and thespeed sensor mounted on the bellhousingover the flywheel. Later Motronic systemshave a single sensor (pulse sensor) mountedover the crankshaft pulley. This sensorfunctions as a speed sensor as well as aposition sensor. Refer to Chapter 5 for moreinformation. Note: Some models areequipped with a TDC sensor mounted on thefront of the engine. This sensor is strictly forthe BMW service test unit, and it is not part ofthe Motronic ignition system.5 Positive crankcaseventilation (PCV) system1 The Positive Crankcase Ventilation (PCV)system(seeillustration)reduceshydrocarbon emissions by scavengingcrankcase vapours. It does this by circulatingblow-by gases and then re-routing them tothe intake manifold by way of the air cleaner.2 This PCV system is a sealed system. Thecrankcase blow-by vapours are routeddirectly to the air cleaner or air collector withcrankcase pressure behind them. The vapouris not purged with fresh air on most models orChec
The Motronic engine management system control unit (computer) has a built-in self-diagnosis system, which detects malfunctions in the system sensors and stores them as fault codes in its memory. It is not possible without dedicated test equi