Subaru 2006 Legacy, Manual

Page: 555 / 4302

GD(H4SO)-11 8
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
3. ENABLE CONDITION
(1) Front oxygen (A/F) sensor (A) Normal (D) Output waveform from the rear
oxygen Sensor
(2) Front oxygen sensor (B) Deterioration
(3) Catalytic converter (C) Output waveform from the front
oxygen (A/F) sensor
Secondary Parameters Enable Conditions
Battery voltage > 10.9 V
Atmospheric pressure > 75.1 kPa (563 mmHg, 22.2
inHg)
Engine coolant temperature
≥
70°C (158°F)
Catalyst warm-up counter (Map 2)
≥
8000
Misfire detection every 200 rotations < 5 times
Learning value of evaporation gas density
≤
0.20
Sub feedback In operation
Evaporative system diagnosis Not in operation
Time of difference (< 0.10) between actual
and target lambda 1000 milliseconds or more
Vehicle speed > 70 km/h (43.5 MPH)
Amount of intake air 10 — 40 g (0.35 — 1.41 oz)/s
Engine load change every 0.5 engine revs. < 0.02 g/rev
Rear oxygen output change from lower than
660 mV to higher than 660 mV Experienced after fuel cut
After engine starting
≥
205 sec.
Purge execution calculated time 5 seconds or more
EN-01713
(A)
(B)
(C) (D)
(1)
(2)
(3)
(3)
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