Subaru Legacy (2005 year). Manual - part 158

EN(H4SO 2.0)(diag)-221

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

CB:DTC P2503 CHARGING SYSTEM VOLTAGE LOW

NOTE:
For diagnostic procedure, refer to DTC P0559. <Ref. to EN(H4SO 2.0)(diag)-222, DTC P2504 CHARGING
SYSTEM VOLTAGE HIGH, Diagnostic Procedure with Diagnostic Trouble Code (DTC).>

15

CHECK HARNESS BETWEEN ECM AND AC-
CELERATOR PEDAL POSITION SENSOR.
1) Connect the ECM connector.
2) Measure the resistance between accelera-
tor pedal position sensor connector and engine 
ground.

Connector & terminal

(B315) No. 4 — Engine ground:
(B315) No. 6 — Engine ground:

Is the resistance less than 5 
Ω?

Go to step 16.

Repair the poor 
contact in ECM 
connector. 
Replace the ECM 
if defective. <Ref. 
to FU(H4SO 2.0)-
34, Engine Con-
trol Module 
(ECM).>

16

CHECK HARNESS BETWEEN ECM AND AC-
CELERATOR PEDAL POSITION SENSOR.
1) Connect the ECM connector.
2) Turn the ignition switch to ON.
3) Measure the voltage between accelerator 
pedal position sensor connector and engine 
ground.

Connector & terminal

(B315) No. 5 (+) — Engine ground (

−

):

(B315) No. 2 (+) — Engine ground (

−

):

Is the voltage less than 6 V?

Go to step 17.

Repair the battery 
short circuit of har-
ness between 
ECM connector 
and accelerator 
pedal position sen-
sor connector.

17

CHECK HARNESS BETWEEN ECM AND AC-
CELERATOR PEDAL POSITION SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance between ECM con-
nectors.

Connector & terminal

(B137) No. 29 — (B137) No. 25:
(B137) No. 29 — (B136) No. 17:
(B137) No. 30 — (B137) No. 25:
(B137) No. 30 — (B136) No. 17:

Is the resistance more than 1 
M

Ω?

Go to step 18.

Repair the short 
circuit to sensor 
power supply.

18

CHECK HARNESS BETWEEN ECM AND AC-
CELERATOR PEDAL POSITION SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Disconnect the connectors from accelerator 
pedal position sensor.
4) Measure the resistance between connector 
terminals of accelerator pedal position sensor.

Connector & terminal

(B315) No. 5 — (B315) No. 2:

Is the resistance more than 1 
M

Ω?

Repair the poor 
contact in ECM 
connector. 
Replace the ECM 
if defective. <Ref. 
to FU(H4SO 2.0)-
34, Engine Con-
trol Module 
(ECM).>

Repair the short 
circuit of harness 
between ECM 
connector and 
accelerator pedal 
position sensor 
connector.

Step

Check

Yes

No

EN(H4SO 2.0)(diag)-222

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

CC:DTC P2504 CHARGING SYSTEM VOLTAGE HIGH

DTC DETECTING CONDITION:
Immediately at fault recognition

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4SO 2.0)(diag)-
38, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO 2.0)(diag)-32, PRO-
CEDURE, Inspection Mode.>.
WIRING DIAGRAM:

EN-02447

B135

F26

F26

ECM

GENERATOR

16

3

1 2 3

B135

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

EN(H4SO 2.0)(diag)-223

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK HARNESS BETWEEN GENERATOR 
AND ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from generator 
and ECM.
3) Measure the resistance of harness 
between generator connector and engine 
ground.

Connector & terminal

(F26) No. 3 — Engine ground:

Is the resistance more than 1 
M

Ω?

Go to step 2.

Repair the ground 
short circuit of har-
ness between 
ECM and purge 
control solenoid 
valve connector.

2

CHECK HARNESS BETWEEN GENERATOR 
AND ECM CONNECTOR.
Measure the resistance of harness between 
ECM and generator.

Connector & terminal

(B135) No. 16 — (F26) No. 3:

Is the resistance less than 1 
Ω?

Repair the poor 
contact in connec-
tor.

Repair the open 
circuit of harness 
between ECM and 
generator connec-
tor.

NOTE:
In this case, repair
the following item:
• Open circuit of 
harness between 
ECM and genera-
tor connector
• Poor contact in 
coupling connector

EN(H4SO 2.0)(diag)-224

ENGINE (DIAGNOSTICS)

General Diagnostic Table

19.General Diagnostic Table

A: INSPECTION

1. ENGINE

NOTE:
Malfunction of parts other than those listed is also possible. <Ref. to ME(H4SO 2.0)-89, Engine Trouble in
General.>

Symptom

Problem parts

1. Engine stalls during idling.

1) Manifold absolute pressure sensor
2) Intake air temperature sensor
3) Ignition parts (*1)
4) Engine coolant temperature sensor (*2)
5) Crankshaft position sensor (*3)
6) Camshaft position sensor (*3)
7) Fuel injection parts (*4)

2. Rough idling

1) Manifold absolute pressure sensor
2) Intake air temperature sensor
3) Engine coolant temperature sensor (*2)
4) Ignition parts (*1)
5) Air intake system (*5)
6) Fuel injection parts (*4)
7) Electronic throttle control
8) Crankshaft position sensor (*3)
9) Camshaft position sensor (*3)
10) Oxygen sensor
11) Fuel pump and fuel pump relay
12) EGR valve

3. Engine does not return to idle.

1) Engine coolant temperature sensor
2) Electronic throttle control
3) Manifold absolute pressure sensor
4) Intake air temperature sensor
5) EGR valve

4. Poor acceleration

1) Manifold absolute pressure sensor
2) Intake air temperature sensor
3) Electronic throttle control
4) Fuel injection parts (*4)
5) Fuel pump and fuel pump relay
6) Engine coolant temperature sensor (*2)
7) Crankshaft position sensor (*3)
8) Camshaft position sensor (*3)
9) A/C switch and A/C cut relay
10) Engine torque control signal circuit
11) Ignition parts (*1)
12) EGR valve

5. Engine stalls, engine sags or hesitates at accel-
eration.

1) Manifold absolute pressure sensor
2) Intake air temperature sensor
3) Engine coolant temperature sensor (*2)
4) Crankshaft position sensor (*3)
5) Camshaft position sensor (*3)
6) Purge control solenoid valve
7) Fuel injection parts (*4)
8) Electronic throttle control
9) Fuel pump and fuel pump relay
10) EGR valve