Subaru Impreza 2003 Service Manual page 1268

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK GROUND CIRCUIT OF ECM.
1)Turn the ignition switch to OFF.
2)Disconnect the connector from ECM.
3)Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B84) No. 8 — Chassis ground:
(B84) No. 9 — Chassis ground:
2 CHECK CURRENT DATA.
1)Start the engine.
2)Read the data of rear oxygen sensor heater
current using Subaru Select Monitor or OBD-II
general scan tool.
NOTE:
•Subaru Select Monitor
For detailed operation procedure, refer to the
"READ CURRENT DATA FOR ENGINE".
<Ref. to EN(H4DOTC)-32, Subaru Select Mon-
itor.>
•OBD-II scan tool
For detailed operation procedures, refer to the
OBD-II General Scan Tool Instruction Manual.
3 CHECK OUTPUT SIGNAL FROM ECM.
1)Start and idle the engine.
2)Measure the voltage between ECM connec-
tor and chassis ground.
Connector & terminal
(B137) No. 13 (+) — Chassis ground ( − − − − ):
4 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B137) No. 13 (+) — Chassis ground ( − − − − ):
5 CHECK OUTPUT SIGNAL FROM ECM.
1)Turn the ignition switch to OFF.
2)Disconnect the connector from rear oxygen
sensor.
3)Measure the voltage between ECM connec-
tor and chassis ground.
Connector & terminal
(B137) No. 13 (+) — Chassis ground ( − − − − ):
Check
Is the resistance less than 5
Ω?
Is the current more than 0.2 A? Repair the con-
Is the voltage less than 1 V?
Shake the ECM harness and
connector, while monitoring
value of voltage meter. Does
the voltage change?
Is the voltage less than 1 V?
EN(H4DOTC)-92
Yes
Go to step 2. Repair the har-
ness and connec-
tor.
NOTE:
In this case, repair
the following:
• Open circuit in
harness between
ECM and engine
ground cable
• Poor contact in
ECM connector
• Poor contact in
coupling connector
Go to step 3.
nector.
NOTE:
In this case, repair
the following:
• Poor contact in
rear oxygen sen-
sor connector
• Poor contact in
rear oxygen sen-
sor connecting
harness connector
• Poor contact in
ECM connector
Go to step 6. Go to step 4.
Repair the poor Go to step 5.
contact in ECM
connector.
Replace the ECM. Repair the battery
<Ref. to short circuit in har-
FU(H4DOTC)-49, ness between
Engine Control ECM and rear oxy-
Module (ECM).> gen sensor con-
nector. After
repair, replace the
ECM. <Ref. to
FU(H4DOTC)-49,
Engine Control
Module (ECM).>
No