Allison Transmission T 280

6.0DIAGNOSTICS
6.1OVERVIEW
Diagnosticfeaturesareprovidedwiththetransmissioncontrolsystemto
assistintroubleshootingofmalfunctionsand/orthemonitoringofspecic
operatingparameters.Whenacontrolsystemmalfunctionisdetected,a
seriesofDiagnosticTroubleCodes(DTCs)areusedtoidentifyandclarifythe
natureofthemalfunction.TheseDTCsareeachnamedbya5character
alphanumericstringthatreferstoadiagnosticalgorithmrunningpass/fail
teststohelpidentifyamalfunctioninthetransmissionorvehicleoperation.
MostDTCshavesomekindofdiagnosticresponsethattheoperatornotices,
suchasanilluminatedCHECKTRANSlight,selectordisplaychange,lock
inrange,orinhibitshiftscondition.
DTCsareloggedintheTransmissionControlModule(TCM)memoryby
severityandbytheiractive/inactivestatuswiththemostsevereandactive
codeslistedrst.AmaximumofveDTCs(numberedd1–d5)frommost
recenttooldestmaybereadfromtheshiftselector.AsDTCsareadded,the
oldestinactiveDTC(historic)isdroppedfromthelist.IfallDTCsareactive,
theDTCwiththelowestpriorityisdroppedfromthelist.
AnactivecodeisanycodethatiscurrentintheTCMdecision-making
processandhasfailedtheDTCtest(s)associatedwiththatspecicdiagnostic
algorithm.Historicalcodes,whicharebydenitioninactive,arecodesthat
arenolongerfailingtheiralgorithmbutareretainedintheTCMinorderto
helpthetechniciananalyzepossiblecausesandprovidethemdirectionifthe
vehicleisbroughtinbeforetheyareclearedfromthequeue.
DTCscanbeclearedmanuallybytheoperatorortheyclearautomatically
fromlast(d5)torst(d1)inthequeueafteranumberofenginestarts,without
becomingactiveagain.
6.2DIAGNOSTICTROUBLECODERESPONSE
Theelectroniccontrolsystemisprogrammedtoinformtheoperatorofa
problemwiththetransmissionsystemviatheCHECKTRANSlightandshift
selectordisplaywhileitautomaticallytakesactiontoprotecttheoperator,
vehicle,andtransmission.WhentheTransmissionControlModule(TCM)
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