Subaru IMPREZA 2004 Service Manual page 764

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 connec-
tor and chassis ground.
Connector & terminal
(B136) No. 4 (+) — Chassis ground (–):
2 CHECK POOR CONTACT.
Check poor contact in ECM connector.
3 CHECK KNOCK SENSOR.
1)Disconnect the connector from knock sensor.
2)Measure the resistance between knock sen-
sor connector terminal and engine ground.
Terminals
No. 2 — Engine ground:
4 CHECK HARNESS CONNECTOR BETWEEN
ECM AND KNOCK SENSOR.
Measure the resistance of harness connector
between ECM and knock sensor.
Connector & terminal
(E14) No. 2 — Chassis ground:
5 CHECK HARNESS CONNECTOR BETWEEN
ECM AND KNOCK SENSOR.
Measure the resistance of harness of harness
connector between ECM connector and knock
sensor.
Connector & terminal
(B136) No. 4 — Chassis ground:
6 CHECK POOR CONTACT.
Check poor contact in ECM connector.
Is the voltage more than 3 V?
Is there poor contact in ECM
connector?
Is the resistance 530 kΩ —
590 kΩ?
Is the resistance less than 1
Ω?
Is the resistance more than 1
MΩ?
Is there poor contact in ECM
connector?
EN(H4SOw/oOBD)(diag)-68
Check
Go to step 2.
Repair the poor
contact in ECM
connector.
Go to step 4.
Go to step 5.
Go to step 6.
Repair the poor
contact in ECM
connector.
Yes No
Go to step 3.
Replace the ECM.
<Ref. to
FU(H4SOw/
oOBD)-43, Engine
Control Module
(ECM).>
Repair the har-
ness and connec-
tor.
NOTE:
In this case, repair
the following:
• Open circuit in
harness between
knock sensor and
ECM connector
• Poor contact in
knock sensor con-
nector
• Poor contact in
coupling connector
(B21)
Replace the knock
sensor. <Ref. to
FU(H4SOw/
oOBD)-31, Knock
Sensor.>
Repair the ground
short circuit
between ECM and
knock sensor.
Replace the ECM.
<Ref. to
FU(H4SOw/
oOBD)-43, Engine
Control Module
(ECM).>