Subaru 2009 IMPREZA, Service Manual

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GD(H4SO)-97
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 CONDITIONS
(A) Normal (C) Output waveform from the front
oxygen (A/F) sensor (D) Output waveform from the rear
oxygen Sensor
(B) Deterioration
(1) Front oxygen (A/F) sensor (2) Front oxygen sensor (3) Catalytic converter
Secondary Parameters Enable Condition
Battery voltage
t
10.9 V
Barometric pressure
t
75 kPa (563 mmHg, 22.2 inHg)
Engine coolant temperature
t
70 °C (158 °F)
Estimated catalyst temperature
t
540 °C (1004 °F)
Misfire detection every 200 rotations < 5 time(s)
Learning value of evaporation gas density < 0.2
Sub feedback In operation
Evaporative system diagnosis Not in operation
Time of difference (< 0.10) between actual
lambda and target lambda
t
1000 ms
Vehicle speed > 70 km/h (43.5 MPH)
Amount of intake air
t
10 g/s (0.35 oz/s)
and
< 40 g/s (1.41 oz/s)
Engine load change every 0.5 engine revs. < 0.02 g/rev (0 oz/rev)
Rear oxygen output change from 660 mV or
less to 660 mV or more Experienced after fuel cut
Elapsed time after starting the engine
t
205 s
Purge execution calculated time
t
0 s
EN-01713
(A)
(B)
(C) (D)
(1)
(2)
(3)
(3)