Subaru Legacy IV (2008 year). Service manual — part 408
GD(H4DOTC)-82
Diagnostic Trouble Code (DTC) Detecting Criteria
GENERAL DESCRIPTION
3. GENERAL DRIVING CYCLE
• If conditions are met, it is possible to detect the misfires from idling to high engine speed. However, to
avoid excessive load or harm to the engine, perform diagnosis at idle.
• Perform the diagnosis continuously.
4. DIAGNOSTIC METHOD
When a misfire occurs, the engine speed will decreased and the crankshaft position speed will change. Cal-
culate the interval difference value (diagnostic value) from crankshaft position speed by the following formu-
la, and judge whether a misfire is occurring or not comparing the calculated result with judgment value.
Counting the number of misfires. If the misfire ratio is higher during 1000 revs. or 200 revs., Judge corre-
sponding cylinders as NG.
As shown in the following figure, pick a cylinder as the standard and name it omg 0. And the former crank-
shaft position speed is named omg 1, the second former crankshaft position speed is named omg 2, the third
is named omg 3, etc.
Diagnostic value calculation
(Calculate from angle speed)
o
Misfire detection every single ignition
(Compare diagnostic value with judg-
ment value)
o
NG judgment (Misfire occurrence judg-
ment required by the law) (Compare
number of misfire with judgment)
• 180° Interval Difference Method
• 360° Interval Difference Method
• 720° Interval Difference Method
• FTP 1.5 times misfire NG judgment
• Catalyst damage misfire NG judgment
(A)
Ignition order
(B)
Crankshaft position speed
EN-01774
#3
#2
#4
#1
#3
#2
#4
#1
#3
#2
(A)
(B)
omg0
omg1
omg2
omg3
omg4
omg5
omg6
omg7
GD(H4DOTC)-83
Diagnostic Trouble Code (DTC) Detecting Criteria
GENERAL DESCRIPTION
180° Interval Difference Method
360° Interval Difference Method
Diagnostic value domg 180 = (omg 1 – omg 0) – (omg 5 – omg 1)/4
Judge as a misfire in the following cases.
• domg 180 > judgment value of positive side
• domg 180
d judgment value of negative side
(Judgement value before 180° CA)
Diagnostic value domg 360 = (omg 1 – omg 0) – (omg 3 – omg 2)
Misfire judgment domg 360 > Judgement value
o Judge as misfire
Judged as misfire.
Threshold valve (positive number)
Threshold valve (negative number)
domg180
domg180
EN-02877
Judged as misfire.
Threshold valve
domg360
domg360
EN-03273
GD(H4DOTC)-84
Diagnostic Trouble Code (DTC) Detecting Criteria
GENERAL DESCRIPTION
720° Interval Difference Method
• FTP 1.5 times misfire (Misfire occurrence level which influences exhaust gas)
• Abnormality Judgement
Time Needed for Diagnosis: 1000 engine revs.
Malfunction Indicator Light Illumination: Illuminates when malfunction occurs in 2 continuous driving cy-
cles.
• Normality Judgement
Time Needed for Diagnosis: 1000 engine revs.
Diagnostic value domg 720 = (omg 1 – omg 0) – (omg 5 – omg 4)
Misfire judgment domg 720 > Judgement value
o Judge as misfire
Judgement Value (Judge that malfunction occurs when the misfire ratio is high in 1000 engine revs.)
Malfunction Criteria
Threshold Value
FTP emission judgment value
t 20 × 100/2000% in
1000 revs.
Judgement Value
Malfunction Criteria
Threshold Value
FTP emission judgment value
< 20 × 100/2000% in
1000 revs.
Judged as misfire.
Threshold valve
domg720
domg720
EN-03274
GD(H4DOTC)-85
Diagnostic Trouble Code (DTC) Detecting Criteria
GENERAL DESCRIPTION
• Catalyst damage misfire (Misfire occurrence level damaging catalyst)
• Abnormality Judgement
Map 3
Time Needed for Diagnosis: 200 engine revs.
Malfunction Indicator Light Illumination: Illuminates as soon as a malfunction occurs.
• Normality Judgement
Time Needed for Diagnosis: 200 engine revs.
AT:DTC P0302 CYLINDER 2 MISFIRE DETECTED
1. OUTLINE OF DIAGNOSIS
NOTE:
For the detection standard, refer to DTC P0301. <Ref. to GD(H4DOTC)-80, DTC P0301 CYLINDER 1 MIS-
FIRE DETECTED, Diagnostic Trouble Code (DTC) Detecting Criteria.>
AU:DTC P0303 CYLINDER 3 MISFIRE DETECTED
1. OUTLINE OF DIAGNOSIS
NOTE:
For the detection standard, refer to DTC P0301. <Ref. to GD(H4DOTC)-80, DTC P0301 CYLINDER 1 MIS-
FIRE DETECTED, Diagnostic Trouble Code (DTC) Detecting Criteria.>
AV:DTC P0304 CYLINDER 4 MISFIRE DETECTED
1. OUTLINE OF DIAGNOSIS
NOTE:
For the detection standard, refer to DTC P0301. <Ref. to GD(H4DOTC)-80, DTC P0301 CYLINDER 1 MIS-
FIRE DETECTED, Diagnostic Trouble Code (DTC) Detecting Criteria.>
Judgement Value
Malfunction Criteria
Threshold Value
Catalyst damage misfire judgment value
t Value from Map 3
Intake
air
(g(oz)/rev)
0.2
(0.01)
0.4
(0.01)
0.6
(0.02)
0.8
(0.03)
1
(0.04)
1.2
(0.04)
1.4
(0.05)
1.6
(0.06)
1.8
(0.06)
2
(0.07)
Engine
speed
(rpm)
700
148
128
116
106
100
90
90
90
90
90
1000
148
128
114
104
92
85
85
85
85
85
1500
140
118
102
90
85
85
85
72
72
72
2000
128
90
90
73
58
43
40
36
32
20
2500
116
87
57
45
39
36
34
32
30
20
3000
108
87
58
39
36
36
32
30
28
20
3500
98
74
43
27
23
22
20
20
20
20
4000
69
61
40
27
22
20
20
20
20
20
4500
60
55
34
25
20
20
20
20
20
20
5000
55
55
34
23
20
20
20
20
20
20
5500
54
54
33
22
20
20
20
20
20
20
6000
52
52
32
21
20
20
20
20
20
20
6500
50
50
30
20
20
20
20
20
20
20
6700
50
50
30
20
20
20
20
20
20
20
Judgement Value
Malfunction Criteria
Threshold Value
Catalyst damage misfire judgment value
< Value from Map 3
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