Subaru LEGACY 2006 Manual page 555

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Diagnostic Trouble Code (DTC) Detecting Criteria
GENERAL DESCRIPTION
BE:DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)
1. OUTLINE OF DIAGNOSIS
Detect the deterioration of the catalyst function.
Though the front oxygen sensor output would change slowly with a new catalyst, the sensor output with a de-
teriorated catalyst becomes high and the inversion time is shortened.
For this reason, the catalyst diagnosis is carried out by monitoring the front oxygen sensor output and com-
paring it with the front oxygen (A/F) sensor output.
2. COMPONENT DESCRIPTION
(A)
(B)
(1) Front oxygen (A/F) sensor
(2) Front oxygen sensor
(3) Catalytic converter
3. ENABLE CONDITION
Secondary Parameters
Battery voltage
Atmospheric pressure
Engine coolant temperature
Catalyst warm-up counter (Map 2)
Misfire detection every 200 rotations
Learning value of evaporation gas density
Sub feedback
Evaporative system diagnosis
Time of difference (< 0.10) between actual
and target lambda
Vehicle speed
Amount of intake air
Engine load change every 0.5 engine revs.
Rear oxygen output change from lower than
660 mV to higher than 660 mV
After engine starting
Purge execution calculated time
(1)
(3)
(3)
(C)
(A) Normal
(B) Deterioration
(C) Output waveform from the front
oxygen (A/F) sensor
Enable Conditions
> 10.9 V
> 75.1 kPa (563 mmHg, 22.2
inHg)
≥ 70°C (158°F)
≥ 8000
< 5 times
≤ 0.20
In operation
Not in operation
1000 milliseconds or more
> 70 km/h (43.5 MPH)
10 — 40 g (0.35 — 1.41 oz)/s
< 0.02 g/rev
Experienced after fuel cut
≥ 205 sec.
5 seconds or more
GD(H4SO)-118
(2)
(D)
(D) Output waveform from the rear
oxygen Sensor
EN-01713