Toyota Camry Manual page 1335

DI–308
DTC P0420
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.
Waveform of
A/F Sensor
DTC No.
After engine and catalyst are warmed up, and while vehicle is
driven within set vehicle and engine speed range, waveform of
P0420 heated oxygen sensor (bank 1 sensor 2) alternates flatteringly
between rich and lean
(2 trip detection logic)
DIAGNOSTICS
Catalyst System Efficiency Below Threshold
(Only for California Spec.)
DTC Detecting Condition
– ENGINE (1MZ–FE)
Normal Catalyst
Abnormal Catalyst
D Three–way catalytic converter
D Open or short in heated oxygen sensor
(bank 1 sensor 2) circuit
D Heated oxygen sensor (bank 1 sensor 2)
D Open or short in A/F sensors (bank 1, 2 sensor 1) circuit
D A/F sensors (bank 1, 2 sensor 1)
Author :
Waveform of Heated Oxygen
Sensor Behind Catalyst
Trouble Area
Date :
DI1K4–03
A01674
543