ft丰田卡罗拉corolla维修手册带电路图po420.pdf

05–186

DIAGNOSTICS–SFISYSTEM(April,2003)05DIP–01

DTCP0420CATALYSTSYSTEMEFFICIENCYBELOW

THRESHOLD(BANK1)

CIRCUITDESCRIPTION

TheECMcomparesthetwowaveformsoftheheatedoxygensensorslocatedbeforeandafterthecatalyst

todeterminewhetherornotthecatalystperformancehasdeteriorated.

Air–fuelratiofeedbackcompensationkeepsthewaveformoftheheatedoxygensensorinfrontofthecata-

lystalternatesbetweenbackandforth,fromrichtolean.

Ifthecatalystisfunctioningnormally,thewaveformoftheheatedoxygensensorbehindthecatalystswitches

backandforthbetweenrichandleanmuchmoreslowlythanthewaveformoftheheatedoxygensensor

infrontofthecatalyst.

Whenbothwaveformschangeatasimilarrate,itindicatesthatthecatalystperformancehasdeteriorated.

MONITORDESCRIPTION

Thevehicleisequippedwiththetwooxygensensors(O2S).Oneismountedupstreamfromthethree–way

catalytic(TWC)converter(frontheatedoxygensensor”sensor1”),thesecondismounteddownstream

(heatedoxygensensor”sensor2”).Thecatalystefficiencymonitorcomparesthesensor1and2signals

inordertocalculateTWCabilitytostoreoxygen.

Duringnormaloperation,theTWCstoresandreleasesoxygenasneeded.Thisresultsinlowoxygenvaria-

tionsinthepostTWCexhauststreamasshown.

WaveformofHeatedWaveformofHeated

OxygenSensorOxygenSensor

(beforeCatalyst)(afterCatalyst)

NormalCatalyst

Wa