Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Service manual — part 295
EN(H4DOTC)(diag)-404
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
ECM
6
4 5
3
2
1
*
2
1
B220
15A
9
10
11
12
B220
*
*
1 2
3 4
D1
36
D3 A4
40
34
35
B21
E2
A6
A3
B220
13
14
15 16
17
27
24
25
26
20
21
22
23
29
30
31
28
32 35
33
34
37
38
39
36
40
8
9
10
11 12
1
2
5
3
4
7
6
19
18
B134
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
A:
D: B137
C: B136
B: B135
A:
T6
B134
C9
B30
C20
B6
*
*
B21
1 2 3 4
12 13 14 15
5 6 7 8
16 17 18 19
9 10 11
20 21 22
23 24 25 26 27 28 29 30 31 32 33
35
34
37
36
39
38
41
40
43
42
44 45
47
46
49
48
51
50
53
52
54
4
1
3
4
1
3
B19
T5
22
T5
B19
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
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
29 30 31
32 33
34 35
B136
C:
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
35
D: B137
B19
T6
B83
B138
B138
B83
EN-08723
SBF-5
E
E
BATTERY
: TERMINAL No. OPTIONAL ARRANGEMENT
REAR
OXYGEN SENSOR
A/F, OXYGEN SENSOR
RELAY
FUSE
(RELAY BLOCK)
EN(H4DOTC)(diag)-405
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
Step
Check
Yes
No
1
CHECK FRONT OXYGEN (A/F) SENSOR
CONNECTOR AND COUPLING CONNEC-
TOR.
Has water entered the connec-
tor?
Completely
remove any water
inside.
2
CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM and
front oxygen (A/F) sensor.
3) Measure the resistance of harness between
ECM connector and front oxygen (A/F) sensor
connector.
Connector & terminal
Models without SI-DRIVE
(B136) No. 19 — (E22) No. 1:
(B136) No. 18 — (E22) No. 3:
Models with SI-DRIVE
(B136) No. 19 — (B379) No. 4:
(B136) No. 18 — (B379) No. 3:
Is the resistance less than 1 Ω? Go to step
Repair the harness
and connector.
NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM
connector
and front oxygen
(A/F) sensor con-
nector
• Poor contact of
coupling connector
ECM
EN-08718
#4
2
1
#3
2
1
#2
2
1
B21
#1
2
1
4
8
54
53
52
51
10
11
12
13
1 2
B21
E5
E5
E2
E6
E6
E16
E16
E17
E17
B134
1 2 3 4
12 13 14 15
5 6 7 8
16 17 18 19
9 10 11
20 21 22
23 24 25 26 27 28 29 30 31 32 33
35
34
37
36
39
38
41
40
43
42
44 45
47
46
49
48
51
50
53
52
54
B220
24
23
22
15A
B220
3
4
21
B134
31
30
32
29
34
33
21
20
19
18
17
16
28
27
26
15
14
13
12
11
25
23
22
24
10
3
4
9
1
2
8
7
6
5
B220
18
19
6
7
4
3
5
2
1
12
11
10
9
8
40
36 39
38
37
34
33
35
32
28 31
30
29
23
22
21
20
26
25
24
27
17
16
15
14
13
E
SBF-7
MAIN RELAY
FUSE
(RELAY BLOCK)
FUEL INJECTOR
BATTERY
EN(H4DOTC)(diag)-406
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
3
CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
Measure the resistance between ECM connec-
tor and chassis ground.
Connector & terminal
(B136) No. 19 — Chassis ground:
(B136) No. 18 — Chassis ground:
Is the resistance 1 MΩ or
more?
Repair the short
circuit to ground in
harness between
ECM connector
and front oxygen
(A/F) sensor con-
nector.
4
CHECK OUTPUT SIGNAL FOR ECM.
1) Connect the connector to ECM.
2) Turn the ignition switch to ON.
3) Measure the voltage between front oxygen
(A/F) sensor connector and chassis ground.
Connector & terminal
Models without SI-DRIVE
(E22) No. 1 (+) — Chassis ground (–):
Models with SI-DRIVE
(B379) No. 4 (+) — Chassis ground (–):
Is the voltage 4.5 V or more?
5
CHECK OUTPUT SIGNAL FOR ECM.
Measure the voltage between front oxygen (A/
F) sensor connector and chassis ground.
Connector & terminal
Models without SI-DRIVE
(E22) No. 3 (+) — Chassis ground (–):
Models with SI-DRIVE
(B379) No. 3 (+) — Chassis ground (–):
Is the voltage 4.95 V or more? Go to step
6
CHECK OUTPUT SIGNAL FOR ECM.
Measure the voltage between front oxygen (A/
F) sensor connector and chassis ground.
Connector & terminal
Models without SI-DRIVE
(E22) No. 3 (+) — Chassis ground (–):
(E22) No. 1 (+) — Chassis ground (–):
Models with SI-DRIVE
(B379) No. 3 (+) — Chassis ground (–):
(B379) No. 4 (+) — Chassis ground (–):
Is the voltage 8 V or more?
Repair the poor
contact of ECM
connector.
7
CHECK EXHAUST SYSTEM.
Are there holes or loose bolts
on exhaust system?
Repair the exhaust
system.
8
CHECK AIR INTAKE SYSTEM.
Are there holes, loose bolts or
disconnection of hose on air
intake system?
Repair the air
intake system.
Step
Check
Yes
No
EN(H4DOTC)(diag)-407
Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
9
CHECK FUEL PRESSURE.
WARNING:
Place “NO OPEN FLAMES” signs near the
working area.
CAUTION:
Be careful not to spill fuel.
1) Connect the front oxygen (A/F) sensor con-
nector.
2) Measure the fuel pressure while discon-
necting pressure regulator vacuum hose from
intake manifold. <Ref. to ME(STI)-25, INSPEC-
TION, Fuel Pressure.> <Ref. to ME(w/o STI)-
24, INSPECTION, Fuel Pressure.>
CAUTION:
Release fuel pressure before removing the
fuel pressure gauge.
NOTE:
If fuel pressure does not increase, squeeze the
fuel return hose 2 to 3 times, then measure fuel
pressure again.
Is the measured value 284 —
314 kPa (2.9 — 3.2 kg/cm
2
, 41
— 46 psi)?
Check the fuel
pump and fuel
delivery line.
• Models without
SI-DRIVE <Ref. to
FU(w/o STI)-79,
INSPECTION,
Fuel Pump.> <Ref.
to FU(w/o STI)-93,
INSPECTION,
Fuel Delivery,
Return and Evapo-
ration Lines.>
• Models with SI-
DRIVE <Ref. to
FU(STI)-81,
INSPECTION,
Fuel Pump.> <Ref.
to FU(STI)-97,
INSPECTION,
Fuel Delivery,
Return and Evapo-
ration Lines.>
10
CHECK FUEL PRESSURE.
After connecting the pressure regulator vacuum
hose, measure fuel pressure. <Ref. to ME(STI)-
25, INSPECTION, Fuel Pressure.> <Ref. to
ME(w/o STI)-24, INSPECTION, Fuel Pres-
sure.>
CAUTION:
Release fuel pressure before removing the
fuel pressure gauge.
NOTE:
• If fuel pressure does not increase, squeeze
fuel return hose 2 to 3 times, then measure fuel
pressure again.
• If the measured value at this step is out of
specification, check or replace pressure regula-
tor vacuum hose.
Is the measured value 230 —
260 kPa (2.4 — 2.7 kg/cm
2
, 33
— 38 psi)?
Check the fuel
pump and fuel
delivery line.
• Models without
SI-DRIVE <Ref. to
FU(w/o STI)-79,
INSPECTION,
Fuel Pump.> <Ref.
to FU(w/o STI)-93,
INSPECTION,
Fuel Delivery,
Return and Evapo-
ration Lines.>
• Models with SI-
DRIVE <Ref. to
FU(STI)-81,
INSPECTION,
Fuel Pump.> <Ref.
to FU(STI)-97,
INSPECTION,
Fuel Delivery,
Return and Evapo-
ration Lines.>
Step
Check
Yes
No
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