Subaru Impreza 2003 Service Manual page 866

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
ENGINE (DIAGNOSTICS)
Step
1 CHECK INPUT SIGNAL FOR ECM.
1)Turn the ignition switch to ON.
2)Measure the voltage between ECM and
chassis ground.
Connector & terminal
(B136) No. 12 (+) — Chassis ground (–):
2 CHECK POOR CONTACT.
3 CHECK HARNESS BETWEEN CO RESIS-
TOR AND ECM CONNECTOR.
1)Turn the ignition switch to OFF.
2)Disconnect the connector from ECM and CO
resistor.
3)Measure the resistance of harness between
ECM and CO resistor connector.
Connector & terminal
(B136) No. 15 — (B155) No. 1:
(B136) No. 12 — (B155) No. 2:
(B136) No. 16 — (B155) No. 3:
4 CHECK HARNESS BETWEEN CO RESIS-
TOR AND ECM CONNECTOR.
Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B136) No. 15 — Chassis ground:
(B136) No. 12 — Chassis ground:
(B136) No. 16 — Chassis ground:
5 CHECK CO RESISTOR.
Measure the resistance between CO resistor
terminals.
Terminals
No. 1 — No. 3:
6 CHECK CO RESISTOR.
Measure the variable resistance between CO
resistor terminals while rotating the screw of
CO resistor.
Terminals
No. 1 — No. 2:
Check
Is the voltage 0.5 — 4.5 V?
Is there poor contact in ECM
connector?
Is the resistance less than 1
Ω?
Is the resistance more than 1
MΩ?
Is the resistance 4 — 6 kΩ?
Is the resistance 0 — 6 kΩ?
EN(H4SOw/oOBD)-90
Yes
Go to step 3. Go to step 2.
Repair the poor Replace the ECM.
contact in ECM <Ref. to
connector. FU(H4SOw/
oOBD)-43, Engine
Control Module
(ECM).>
Go to step 4. Repair the open
circuit in harness
between ECM and
CO resistor con-
nector.
Go to step 5. Repair the short
circuit in harness
between ECM and
CO resistor con-
nector.
Go to step 6. Replace the CO
resistor.
Replace the ECM. Replace the CO
resistor.
NOTE:
Ensure resistance
varies in response
to screw rotation.
No