Toyota Camry Manual page 1332

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CIRCUIT DESCRIPTION

The ECM compares the waveform of the oxygen sensor located before the catalyst with the waveform of

the oxygen sensor located after the catalyst to determine whether or not catalyst performance has deterio-

Air–fuel ratio feedback compensation keeps the waveform of the oxygen sensor before the catalyst repeat-

edly changing back and forth from rich to lean.

If the catalyst is functioning normally, the waveform of the oxygen sensor after the catalyst switches back

and forth between rich and lean much more slowly than the waveform of the oxygen sensor before the cata-

But when both waveforms change at a similar rate, it indicates that catalyst performance has deteriorated.

Waveform of Oxygen Sensor

before Catalyst

After engine and catalyst are warmed up, and while vehicle is

driven within set vehicle and engine speed range, waveforms

of heated oxygen sensors (bank 1 sensor 1, 2) have the same

(2 trip detection logic)

CONFIRMATION ENGINE RACING PATTERN

Engine Speed

2,500 ∼ 3,000 rpm

Catalyst System Efficiency Below Threshold

(Except California Spec.)

DTC Detecting Condition

ENGINE (1MZ–FE)

Normal Catalyst

D Three–way catalytic converter

D Open or short in heated oxygen sensor circuit

D Heated oxygen sensor

3 min. or so

Waveform of Oxygen Sensor

after Catalyst

Trouble Area

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