Subaru Legacy IV (2008 year). Service manual — part 565
EN(H6DO)(diag)-233
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
Check
Yes
No
1
CHECK CURRENT DATA.
1) Start the engine.
2) Read data of intake manifold absolute pres-
sure signal using Subaru Select Monitor or gen-
eral scan tool.
NOTE:
• SUBARU SELECT MONITOR
For detailed operation procedure, refer to
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H6DO)(diag)-34, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
general scan tool operation manual.
Is the measured value 53.3 kPa
(400 mmHg, 15.75 inHg) or
more?
Make sure that the
EGR valve, mani-
fold absolute pres-
sure sensor and
throttle body are
installed securely.
Go to step 2.
2
CHECK EGR VALVE.
Remove the EGR valve.
Are there holes, plugged piping
or foreign objects caught in the
EGR system?
Repair the EGR
system.
Replace the EGR
valve. <Ref. to
FU(H6DO)-27,
EGR Valve.>
EN(H6DO)(diag)-234
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
CC:DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)
DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H6DO)-106, DTC P0420 CATALYST SYSTEM EFFICIENCY BE-
LOW THRESHOLD (BANK 1), Diagnostic Trouble Code (DTC) Detecting Criteria.>
TROUBLE SYMPTOM:
• Engine stalls.
• Idle mixture is out of specifications.
CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H6DO)(diag)-52,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H6DO)(diag)-44, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:
B47
3
4
5
6
1
2
B22
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
1 2 3 4
5 6 7 8
B83
B138
3 4
1 2
E25
E61
B47
1
2
3
5
4
6
E3
B22
14
MAIN RELAY
2
4
3
1
E25
13
15
16
E3
B22
10
11
12
9
SBF-5
BATTERY
2
E61
4
3
1
*
1
*
1
*
1
B83
B138
ECM
B134
A:
B135
B:
B136
C:
B137
D3
A3
D2
D1
D7
A5
D:
C5
*
*
2
2
C4
E
B1
B15
B4
B30
35
34
52
36
37
B21
E2
E
E
: TERMINAL No. OPTIONAL ARRANGEMENT
*
1
: TERMINAL No. OPTIONAL ARRANGEMENT
AMONG 1, 2, 5 AND 6
*
2
EN-06868
16
10 11 12 13 14 15
25
24
30
9
8
7
17 18 19 20
28
21 22 23
29
32
31
1
2
3
4
5
6
27
26
33 34 35
B136
C:
5
6
7
8
2
1
9
4
3
10
22 23
11 12 13 14 15
24 25
26
16 17
18 19 20 21
27
28 29
30 31
B137
D:
5
6
7
8
2
1
9
4
3
10
24
22 23
25
11 12 13 14 15
26 27
28
16 17 18 19
20 21
29 30 31
32 33
34 35
B135
B:
5
6
7
8
2
1
9
4
3
10
24
22 23
25
11 12 13 14 15
26 27
28
16 17
18 19 20 21
33 34
29
32
30 31
B134
A:
B21
1 2 3 4 5 6 7 8 9 10 11
12 13 14 15 16 17 18 19 20 21 22
23 24 25 26 27 28 29 30 31 32 33
34
35
42
43
36
37
38
39
48
49
50
51
52
53
54
40
41
44
45
46
47
REAR
OXYGEN
SENSOR LH
REAR
OXYGEN
SENSOR RH
EN(H6DO)(diag)-235
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
Check
Yes
No
1
CHECK EXHAUST SYSTEM.
Check for gas leaks or air suction caused by
loose or dislocated nuts and bolts, and open
hole at exhaust pipes.
NOTE:
Check the following positions.
• Between cylinder head and front exhaust
pipe
• Between front exhaust pipe and front catalytic
converter
• Between front catalytic converter and rear
catalytic converter
• Looseness and improper attachment of front
oxygen (A/F) sensor or rear oxygen sensor
Is there any fault in exhaust
system?
Repair or replace
the exhaust sys-
tem. <Ref. to
EX(H6DO)-2, Gen-
eral Description.>
Go to step 2.
2
CHECK WAVEFORM DATA ON THE SUBA-
RU SELECT MONITOR (WHILE DRIVING).
1) Drive at a constant speed between 80 —
112 km/h (50 — 70 MPH).
2) After 5 minutes have elapsed in the condi-
tion of step 1), use the Subaru Select Monitor
while still driving to read the waveform data.
• At normal condition
• At abnormal condition (numerous inversion)
Is normal waveform pattern dis-
played?
Even if DTC is
detected, the cir-
cuit has returned to
a normal condition
at this time. Repro-
duce the failure,
and then perform
the diagnosis
again.
NOTE:
In this case, tem-
porary poor con-
tact of connector
may be the cause.
Go to step 3.
EN-06666
1
0
1.5
0.5
10 sec/div
REAR OXYGEN
SENSOR VOLTAGE
(V)
A/F SENSOR
OUTPUT LAMBDA 1
EN-06667
1
0
1.5
0.5
10 sec/div
REAR OXYGEN
SENSOR VOLTAGE
(V)
A/F SENSOR
OUTPUT LAMBDA 1
EN(H6DO)(diag)-236
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
3
CHECK WAVEFORM DATA ON THE SUBA-
RU SELECT MONITOR (WHILE IDLING).
1) Run the engine at idle.
2) In the condition of step 1), use the Subaru
Select Monitor to read the waveform data.
• At normal condition
• At abnormal condition 1 (numerous inversion)
• At abnormal condition 2 (noise input)
Is normal waveform pattern dis-
played?
Go to step 4.
• The waveform is
displayed at abnor-
mal condition 1:Go
to step 4.
• The waveform is
displayed at abnor-
mal condition 2:Go
to step 5.
4
CHECK CATALYTIC CONVERTER.
Is the catalytic converter dam-
aged?
Replace the cata-
lytic converter.
<Ref. to
EC(H6DO)-3,
Front Catalytic
Converter.>
Go to step 5.
5
CHECK REAR OXYGEN SENSOR CONNEC-
TOR AND COUPLING CONNECTOR.
Has water entered the connec-
tor?
Completely
remove any water
inside.
Go to step 6.
Step
Check
Yes
No
EN-06668
1
0
10 sec/div
REAR OXYGEN
SENSOR VOLTAGE
(V)
EN-06669
1
0
10 sec/div
REAR OXYGEN
SENSOR VOLTAGE
(V)
EN-06670
1
0
10 sec/div
REAR OXYGEN
SENSOR VOLTAGE
(V)
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