followingchoicesisselectedwhentheTCMisprogrammedbythevehicle
OEM:
•StandardPreselects–downshiftsoccursotheenginespeedafterthe
shiftisapproximately300rpmabovetheenginegovernedspeed
•LowPreselects–downshiftsoccursotheenginespeedaftertheshift
isapproximately150rpmabovetheenginegovernedspeed
4.2.2.3ENGINEBRAKEOREXHAUSTBRAKEOPERATION
WhentheTCMdetectstheenginebrakeisenabled,itcommandsuseof
apreselectshiftscheduleinordertoenhanceenginebrakeperformance.
ThedefaultspeedsfortheseshiftsareknownastheAlternateEngineBrake
Preselects.
•AlternateEngineBrakePreselects–downshiftsoccuratengine
speedsapproximatelymidwaybetween1000rpmandtheStandard
Preselectsforyourtransmissionmodel
Asanoption,thepreselectshiftpointsduringenginebrakeoperationcanbe
speciedtobethesamescheduleselectedwhentheTCMisprogrammedby
thevehicleOEMfornon-enginebrakeoperation:
•StandardPreselects–downshiftsoccursotheenginespeedafterthe
shiftisapproximately300rpmabovetheenginegovernedspeed
•LowPreselects–downshiftsoccursotheenginespeedaftertheshift
isapproximately150rpmabovetheenginegovernedspeed
NOTE:SpecifyStandardorLowPreselectswhentheTCMis
programmed.
Thepreselectschedulechosenabovewillbeactivatedfordownshiftsthat
occurwhiletheenginebrakeisactiveanduntiloperationinaspeciedgear
isreached.ThisspeciedgearistheEngineBrakePreselectRangeCMC
thatisprogrammableusingAllisonDOC
®
.IfthisCMCissettoavaluehigher
than2(SecondRange),thendownshiftsfromtheEngineBrakePreselect
Rangeto2(SecondRange)willbemadeasstandard(non-enginebrake)
closedthrottledownshifts.Additionally,iftheTCMisprogrammedtomake
enginebrakepreselectdownshiftsatStandardPreselectsorLowPreselects
speeds,downshiftsbetweentheEngineBrakePreselectedRangetoaneven
lowergearcanbespeciedtousetheAlternateEngineBrakePreselect
downshiftspeeds.Thelowestgeartousethisdownshiftscheduleisalsoa
CMC(AlternateEngineBrakePreselectRange).Ifthisoptionisspeciedand
theAlternateEngineBrakePreselectRangeCMCishigherthan2(Second
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