CIRCUIT DESCRIPTION
The ECM observes the waveform of the heated oxygen sensor located behind the catalyst to determine whether the catalyst is performance has deteriorated.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor located behind the catalyst switches back and forth between rich and lean much more slowly.
When the waveform of the heated oxygen sensor located behind the catalyst alternates flatteringly between rich and lean, it indicates that catalyst performance has deteriorated.

DETECTING CONDITIONS

CONFIRMATION ENGINE RACING PATTERN

(a)	Connect the OBD II scan tool or TOYOTA hand-held tester to the DLC3.
(b)	Start engine and warm it up with all accessories switched OFF until water temp. is stable.
(c)	Race the engine at 2,500 ~ 3,000 rpm for about 3 min.
(d)	When racing the engine at 3,000 rpm for 2 sec. and 2,000 rpm for 2 sec. alternately, check the waveform of the heated oxygen sensor (bank 1 sensor 2).

Step 1

Step 2

Step 3

INSPECTION PROCEDURE
HINT: Read freeze frame data using TOYOTA hand-held tester or OBD II scan tool. Because freeze frame records the engine conditions when the malfunction is detected, when troubleshooting it is useful for determining whether the vehicle was running or stopped, the engine warmed up or not, the air-fuel ratio lean or rich, etc. at the time of the malfunction.

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