Subaru Legacy IV (2008 year). Manual - part 621

GD(H6DO)-104

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

3. ENABLE CONDITION

4. GENERAL DRIVING CYCLE

During deceleration fuel cut from 53 km/h (approx. 33 MPH) or more, perform diagnosis once.
Be careful of vehicle speed and engine speed. (Diagnosis will not be completed if the vehicle speed and en-
gine speed conditions become out of specification due to deceleration.)

5. DIAGNOSTIC METHOD

Measure the pressure values when the enable conditions are established, and perform diagnosis by calcu-
lating those results.
1. Label the intake manifold pressure value as PMOF1, which is observed when enable conditions are es-
tablished, and set the EGR target step to 50 steps (nearly full open).
2. Label the intake manifold pressure value as PMON, which is observed after one second has passed since
EGR target step was set to 50 steps (when the enable conditions were established), and set the EGR target
step to 0.
3. Label the intake manifold pressure as PMOF2, which is observed after one second has passed since EGR
target step was set to 0 (after two seconds have passed since the enable conditions were established).

• Abnormality Judgement

Judge as NG when the following conditions are established.

Time Needed for Diagnosis: 1 time
Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cy-
cles.

Secondary Parameters

Enable Conditions

Elapsed time after starting the engine

t 40 s

Engine coolant temperature

t 75 °C(167 °F)

Engine speed

1200 rpm — 3250 rpm

Intake manifold pressure (absolute pressure)

< 36.7 kPa (275 mmHg, 10.8 inHg)

Ambient air temperature

t 5 °C(41 °F)

Throttle position

< 0.25 °

Battery voltage

t 10.9 V

Barometric pressure

t 75 kPa (563 mmHg, 22.2 inHg)

Vehicle speed

t53 km/h (32.9 MPH)

Fuel shut-off function

In operation

Neutral switch

OFF

After neutral switch ON/OFF change

t Value from Map

No load change (A/C, power steering, lighting, 
rear defogger, heater fan and radiator fan)

t 5000 ms

Map

Engine coolant temperature

°C (°F)

–40

(–40)

–30

(–22)

–20

(–4)

–10

(14)

0

(32)

10

(50)

20

(68)

30

(86)

After neutral switch change

msec

0

0

0

0

0

0

0

0

Engine coolant temperature

°C (°F)

40

(104)

50

(122)

60

(140)

70

(158)

80

(176)

90

(194)

100

(212)

110

(230)

After neutral switch change

msec

0

0

0

0

0

0

0

0

Judgement Value

Malfunction Criteria

Threshold Value

PMON – (PMOF1 + PMOF2)/2

< 1.6 kPa 
(11.8 mmHg, 0.5 inHg)

GD(H6DO)-105

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

• Normality Judgement

Judge as OK and clear the NG if the following conditions are established.

Time Needed for Diagnosis: 1 time

(A)

2000 ms

(C)

1500 ms

(D)

50 step(s)

(B)

1500 

ms

  

  

Judgement Value

Malfunction Criteria

Threshold Value

PMON – (PMOF1 + PMOF2)/2

t 1.6 kPa (11.8 mmHg, 
0.5 inHg)

EN-05568

ON

OFF

(Open)

(Close)

(Open)

(Close)

PMOF1

PMON

PMOF2

Deceleration fuel cut

Diagnosis enable condition

EGR target step

EGR actual step

DIagnostic mode timer

Start dignosis

(D)

(A)

(B)

(C)

Intake manifold pressure
(During normal condition)

GD(H6DO)-106

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

CC: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)

Normal

(C)

Output waveform from the front 
oxygen (A/F) sensor

(D)

Output waveform from the front 
oxygen sensor

(B)

Deterioration

(1)

Front oxygen (A/F) sensor

(2)

Front oxygen sensor

(3)

Catalytic converter

EN-01713

(A)

(B)

(C)

(D)

(1)

(2)

(3)

(3)

GD(H6DO)-107

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

3. ENABLE CONDITION

4. GENERAL DRIVING CYCLE

Perform the diagnosis only once at a constant 60 km/h (37.3 MPH) or higher.

5. DIAGNOSTIC METHOD

After establishing the execution conditions, calculate the front oxygen (A/F) sensor lambda deviation cumu-
lative value (

6 |(sglmd

n

 – sglmd

n–1

 )|) and rear oxygen sensor output voltage deviation cumulative value (

6

|(ro2sad

n

 – ro2sad

n–1

)|) per 32 milliseconds × 4 , and when the front oxygen (A/F) sensor lambda deviation

cumulative value (

6 |(sglmd

n

 – sglmd

n–1

)|) becomes the predetermined value or more, calculate the diag-

nostic value.

• Abnormality Judgement

If the duration of time while the following conditions are met is within the time indicated, judge as NG.

Time Needed for Diagnosis: 30 — 55 seconds
Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cy-
cles.

• Normality Judgement

Judge as OK and clear the NG if the continuous time while the following conditions are established is within
the predetermined time.

Time Needed for Diagnosis: 30 — 55 seconds

Secondary Parameters

Enable Conditions

Battery voltage

t 10.9 V

Atmospheric pressure

t 75 kPa (563 mmHg, 22.2 inHg)

Engine coolant temperature

t 75 °C (167 °F)

Estimated catalyst temperature

t 560 °C (1040 °F)

Misfire detection every 200 rotations

< 7 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

> 60 km/h (37.3 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 speed. < 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 5 s

Judgement Value

Malfunction criteria

Threshold value

6 |(ro2sad

n

 – ro2sad

n–1

)| / 

6 |(sglmd

n

 – 

sglmd

n–1

)|

> 25 

Judgement Value

Malfunction criteria

Threshold value

6 |(ro2sad

n

 – ro2sad

n–1

)| / 

6 |(sglmd

n

 – 

sglmd

n–1

)|

d 25