Subaru Impreza 2003 Service Manual page 499

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
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
(B136) No. 5 — Chassis ground:
(B136) No. 16 — 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(H4SO)-31, Subaru Select Moni-
tor.>
•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
(B136) No. 4 (+) — Chassis ground ( − − − − ):
4 CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.
Connector & terminal
(B136) No. 4 (+) — Chassis ground ( − − − − ):
5 CHECK OUTPUT SIGNAL FROM ECM.
1)Disconnect the connector from rear oxygen
sensor.
2)Measure the voltage between ECM connec-
tor and chassis ground.
Connector & terminal
(B136) No. 4 (+) — 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?
Does the voltage change by
shaking the ECM harness and
connector?
Is the voltage less than 1 V?
EN(H4SO)-87
ENGINE (DIAGNOSTICS)
Yes
Go to step 2. Repair harness
and connector.
NOTE:
In this case, repair
the following:
• Open circuit in
harness between
ECM and engine
ground terminal
• 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 poor con- Go to step 5.
tact in ECM con-
nector.
Replace the ECM. Repair battery
<Ref. to short circuit in har-
FU(H4SO)-48, ness between
Engine Control ECM and rear oxy-
Module (ECM).> gen sensor con-
nector. After
repair, replace the
ECM. <Ref. to
FU(H4SO)-48,
Engine Control
Module (ECM).>
No