Subaru IMPREZA 2004 Service Manual page 739

Step
1 CHECK MAIN RELAY.
1)Turn the ignition switch to OFF.
2)Remove the main relay.
3)Connect the battery to main relay terminals
No. 1 and No. 2.
4)Measure the resistance between main relay
terminals.
Terminals
No. 3 — No. 5:
No. 4 — No. 6:
2 CHECK GROUND CIRCUIT OF ECM.
1)Disconnect the connector from ECM.
2)Measure the resistance of harness between
ECM and chassis ground.
Connector & terminal
(B136) No. 21 — Chassis ground:
(B136) No. 22 — Chassis ground:
(B134) No. 27 — Chassis ground:
(B134) No. 8 — Chassis ground:
(B134) No. 7 — Chassis ground:
(B135) No. 25 — Chassis ground: (MT
model)
(B135) No. 6 — Chassis ground:
3 CHECK INPUT VOLTAGE OF ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B136) No. 9 (+) — Chassis ground (–):
4 CHECK INPUT VOLTAGE OF ECM.
1)Turn the ignition switch to ON.
2)Measure the voltage between ECM connec-
tor and chassis ground.
Connector & terminal
(B135) No. 7 (+) — Chassis ground (–):
5 CHECK HARNESS BETWEEN ECM AND
MAIN RELAY CONNECTOR.
1)Turn the ignition switch to OFF.
2)Measure the resistance between ECM and
chassis ground.
Connector & terminal
(B135) No. 19 — Chassis ground:
6 CHECK OUTPUT VOLTAGE FROM ECM.
1)Connect the connector to ECM.
2)Turn the ignition switch to ON.
3)Measure the voltage between ECM connec-
tor and chassis ground.
Connector & terminal
(B135) No. 19 (+) — Chassis ground (–):
7 CHECK INPUT VOLTAGE OF MAIN RELAY.
Check the voltage between main relay connec-
tor and chassis ground.
Connector & terminal
(B47) No. 2 (+) — Chassis ground (–):
Diagnostics for Engine Starting Failure
Is the resistance less than 10
Ω?
Is the resistance less than 5
Ω?
Is the voltage more than 10 V? Go to step 4.
Is the voltage more than 10 V? Go to step 5.
Is the resistance more than 1
MΩ?
Is the voltage more than 10 V? Go to step 7.
Is the voltage more than 10 V? Go to step 8.
EN(H4SOw/oOBD)(diag)-43
Check
Go to step 2.
Go to step 3.
Go to step 6.
ENGINE (DIAGNOSTICS)
Yes No
Replace the main
relay.
Repair the open
circuit in harness
between ECM
connector and
engine grounding
terminal.
Repair the open or
ground short cir-
cuit of power sup-
ply circuit.
Repair the open or
ground short cir-
cuit of power sup-
ply circuit.
Repair the ground
short circuit in har-
ness between
ECM connector
and main relay
connector, and
then replace the
ECM.
Replace the ECM.
Repair the open
circuit in harness
between ECM
connector and
main relay connec-
tor.