Throttle-by-wire

MasterCraft Technical TrainingVonore, Tennessee USA

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Engine Control Module (ECM) The Engine Control Module (ECM), located on theengine,isthecontrolcenterofthefuelinjectionsystem.Itcontrolsthefollowing:• Fuelmeteringsystem• Ignitiontiming• Idlespeed• On-boarddiagnosticsforenginefunctions• Boatspeed• Throttleposition Itconstantlylooksattheinformationfromvarioussen-sors,andcontrolsthesystemsthataffectengineperfor-mance.TheECMalsoperformsthediagnosticfunctionofthesystem.Itcanrecognizeoperationalproblems,alertthedriver through theMalfunction IndicatorLamp(MIL)and store diagnostic trouble codes which identify theproblemareastoaidthetechnicianinmakingrepairs.

Electronic Throttle Control Descriptionreprinted by permission from

Indmar Marine Engines manual

Electronic Throttle Control (ETC) Components The Electronic Throttle Control (ETC) system usestheboatelectronicsandcomponentsinordertocalcu-lateandcontrol thepositionof the throttleblade.Thissystemeliminates theneed foramechanicalcableat-tachment from the Throttle-Shift Control (T-SC) to theelectronicthrottlebodyassembly. TheETCsystemcomponentsincludethefollowing:• TheECM• The Throttle Position Sensor (TPS) is located in a

sealedhousing,whichismountedtothesideof theelectronicthrottlebodyassembly.

• TheThrottleActuatorControl(TAC)motorislocatedwithinthesamesealedhousingastheTPS.

• ThePedalPositionSensor(PPS)islocatedwithinasealedhousingmountedtotheThrottle-ShiftControl(T-SC).

Eachofthesecomponentsinterfacetogetherinordertoensureaccuratecalculations,andinordertocontrolthethrottleposition.

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ECM Function TheECMsupplieseither5or12voltstopowervari-oussensorsorswitches.ThisisdonethroughresistanceintheECMwhichissohighinvaluethatatestlightwillnot illuminate when connected to the circuit. In somecases, anordinary voltmeterwill not giveanaccuratereadingbecauseitsresistanceistoolow.Therefore,adigitalvoltmeterwithatleast10megohmsinputimped-ance is required to ensure accurate voltage readings.ToolJ39978,Fluke78orFluke87meetsthisrequire-ment.TheECMcontrolsoutputcircuitssuchasthein-jectors, relays, etc by controlling the ground or powerfeedcircuit. TheECMalsocontrols theElectronicThrottleCon-trol(ETC).TheECMmonitorsthecommandedthrottlepositionandcomparesthecommandedpositiontotheactualthrottleposition.Thisisaccomplishedbymonitor-ing the Pedal Position Sensors (PPS) (located on theThrottle-ShiftControl [T-SC]) and theThrottlePositionSensors(TPS).Thesetwovaluesmustbewithinacali-bratedvalueofeachother.TheECMalsomonitorseachindividualcircuitoftheTPSs,andofthePPSstoverifyproperoperation(thePedalPositionSensorreadsthedegreeofmovementoftheThrottle-ShiftControlfrom0degreesatlockedneutral,to120degreesatWideOpenThrottle[WOT]).

Electronic Throttle Body Assembly

The Electronic Throttle Body Assembly consists oftheelectronicthrottlebody,theThrottlePositionSensors(2),andtheThrottleActuationControl(TAC)motor.Thethrottlebodyhasasealedhousingmountedtothesideofit,whichcontainsthetwoThrottlePositionSensors(TPS)andtheThrottleActuationControl(TAC)motor.Theelec-tronicthrottlebodyassemblyisconnectedtotheECMbyasingle6pinconnectortothewiringharness.

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Throttle Position Sensor (TPS) TheThrottlePositionSensor(TPS)andtheThrottleActuation Control (TAC) motor are contained within asealedhousingmountedonto thesideof theelectron-ic throttle body assembly. If one of these componentsshouldbecomedefectivetheelectronicthrottlebodyas-semblymustbereplacedasacompleteunit. TheTPSisactuallytwoindividualsensorswithintheabovementionedsealedhousing.TheTPSsusetwosep-aratesignalcircuits;howeverthetwosensorsshareonelowreferencecircuitandone,5voltreferencecircuit. TheTPSsignalvoltageispulleduptothereferencevoltageasthethrottleopens,from~0.6voltsatclosedthrottle to~4.3voltsatwideopen throttle (WOT).TheTPS 2 signal voltage is pulled down to the referencevoltageasthethrottleopens,from~4.3voltsatclosedthrottleto~0.6voltsatWOT. TPS1andPedalPositionSensor(PPS)1sharea5voltreferencecircuitthatisconnectedwithintheECM.TPS2andPedalPositionSensor(PPS)2alsosharea5voltreferencecircuitthatisconnectedwithintheECM. ThePPS1signalvoltageispulleduptothereferencevoltageasthethrottleopens,from~0.45voltsatclosedthrottleto~4.18voltsatwideopenthrottle(WOT).ThePPS 2 signal voltage is pulled down to the referencevoltageasthethrottleopens,from~4.55voltsatclosedthrottleto~0.82voltsatWOT.

Throttle Actuation Control (TAC) Motor TheThrottleActuationControl (TAC)motorand theTPSs are located within one sealed housing mountedonto the side of the electronic throttle body. If one ofthesecomponents shouldbecomedefective, theelec-tronic throttle body assembly must be replaced as acompleteunit.TheunitisconnectedtotheECMbyone6pinconnector. TheTACmotorisusedtocontrolthethrottlepositioninsteadofamechanical cable.Thissystemeliminatestheneedforamechanicalcable.Thissystemeliminatesthe need for a mechanical cable attachment from theT-SCtotheelectronicthrottlebodyassembly.TheTAXmotoralsocontrolsthethrottleopeningforidleandcoldstart/fastidlefunctions,therebyeliminatingtheneedforanIdleAirControl(AC)valve.

Pedal Position Sensor ThePedalPositionSensor(PPS)ismountedontheT-SC.ThePPS isactually two individualpositionsen-sors within one housing. The PPSs use two separatesignalcircuits,twolowreferences,andtwo5voltrefer-encecircuitstoconnectthePPSstotheECM. Note:ThetwoPPSsoperateinslightlydifferentvolt-ageranges.Somevariation involtageaboveorbelowthenormalcalibrationisacceptable,howevermorethanapproximately0.15voltswillsetaPPS1-2CorrelationFault. ThePPS1voltageshouldincreasefrombelow1voltatclosedthrottletoabove3.75voltsatWOT. The PPS 2 voltage should decrease from below 5voltsatclosedthrottletoabove1voltatWOT.

Remote Mount Pedal Position Sensor (Typical)

Throttle Cable Interconnect

Throttle-Shift Control (T-SC)

The productionThrottle-Shift Control (T-SC) unit issetupfordualfunctioninasinglelever.Itcontrolsbothshiftingandthrottlebyamechanicalcableandbyelec-tronicthrottlemovement.Addedfeaturesincludeaneu-tralinterlocktohelppreventaccidentalshiftingandcrisppositive detents. Also, the control has a push buttonclutchdisengagementfeatureforwarm-upandstart-upadjustments for increased throttle.The throttle controlisdesignedwithneutralasthecenterlocationandisingearwhentheleverismovedforwardtocrisppositivedetentthirtydegrees.Thetransmissioncableispulledwithaone-to-oneratioastheleverrotatesforthethirtydegreeswhilethethrottlebladeisintheclosedposition.After the first thirty-five degrees, the throttle blade will begintomoveandthetransmissioncablewillstayatthethirtydegreelocation.Maximumthrottleisapproximate-ly one hundred twenty-five degrees. Reverse works in thesamemanner.

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Electronic Throttle Control (ETC) Basics Function: Replaces the mechanical cable link from the Throttle-Shift Control (T-SC) to electronic throttlebodyassemblywithasystemofsensorsandcomputercontrolledthrottle.

Components: Throttle Position Sensor (TPS 1 & 2):These twoindividualsensorsarehousedtogetherwithoneThrottleActuationControl(TAC)motorwithinonesealedcom-partment. That sealed compartment is permanentlymountedtothesideoftheelectronicthrottlebody.Thereisone,6wire,connectorplugleadingfromtheelectronicthrottlebodytothemainwiringharnessandeventuallytotheECM.

Pedal Position Sensor (PPS 1 & 2):Thesetwoindi-vidualsensorsarehousedtogetherinonesealedcom-partment.ThatcompartmentispermanentlyattachedtotheaftendoftheT-SC.Thereisone,sixwire,connectorplugleadingdirectlyfromtheT-SCtotheECM.

ECM: The ECM is the control center for the Elec-tronicThrottleControl(ETC)systemaswellastherestoftheengineelectronics.ItcommunicatesbetweenthedifferentsensorsandtheTACmotor.Itconstantlymoni-torsthesensorreadings. TheECMcontinuouslycompares thevoltage read-ingsbetweenTPS1andTPS2.Itlooksforanyvariancefromtheirnormaloperatingvoltageranges.IfvarianceisfoundaTPS1-2 Correlationfaultisset. The ECM also monitors bothTPS 1 andTPS 2 incaseofadisconnectedcondition. Ifoneof thesesen-sorsshouldbecomedisconnected,thenaTPS 1 Out of RangeoraTPS 2 Out of Rangefaultwillset.AnETCLimitedAuthoritywillalsoset(seeDiagnosingtheETCsystembelowforexplanation).Ifthisoccurstheenginegoestoidle.

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Additionally,theECMcontinuouslycomparesthevolt-agereadingsbetweenPPS1andPPS2.Itwatchesforanyvariancefromtheirnormaloperatingvoltageranges.IfvarianceisfoundaPPS 1-2 Correlationfaultwillset. The ECM also monitors both PPS 1 and PPS 2 incaseofadisconnectedcondition. Ifoneof thesesen-sorsbecomesdisconnected,theneitheraPPS 1 Out of RangeoraPPS 2 Out of Rangefaultwillset.AnETC Limited Authoritywillalsoset(seeDiagnosingtheETCsystembelowforexplanation).Ifthisoccurstheenginegoesintopowerreductionmode. The ECM compares the predicted throttle positionand the actual throttle position. The predicted throttlepositionistheamountofthrottlecalledforbythepedalpositionsensor,which indicateshowmuch throttle thedriverwants.Theactual throttleposition is thecurrentlocation(angle)ofthethrottlebladeinthethrottlebody. The ECM continuously compares the commandedthrottlepositionandtheactualthrottleposition.Thecom-mandedthrottlepositionistheamountofthrottle(degreeofanglethethrottlebladeissetat)calledforbythelo-cationof theThrottle-ShiftControl (T-SC) fromneutraltoWideOpenThrottle(WOT).Theactualthrottleposi-tionisthecurrentexactlocationorangleofthethrottleblade. TheECMcontinuouslyteststheintegrityofthedatawithinitself.IfthereisalossofintegrityintheECMdata,or an inability to write or read data to and from the RAM, or an inability to correctly read data from the flash mem-ory, or an internal ECM processor fault, then an ETC Processfaultsets.

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