Subaru IMPREZA 2004 Service Manual page 78

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
1 CHECK HARNESS BETWEEN KNOCK SEN-
SOR AND ECM CONNECTOR.
Measure the resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B135) No. 16 — Chassis ground:
2 CHECK KNOCK SENSOR.
1)Disconnect the connector from knock sensor.
2)Measure the resistance between knock sen-
sor connector terminal and engine ground.
Terminal
No. 2 — Engine ground:
3 CHECK INPUT SIGNAL FOR ECM.
1)Connect the connectors to ECM and knock
sensor.
2)Turn the ignition switch to ON.
3)Measure the voltage between ECM and
chassis ground.
Connector & terminal
(B135) No. 16 (+) — Chassis ground ( − − − − ):
Check
Is the resistance less than 400
kΩ?
Is the resistance less than 400
kΩ?
Is the voltage more than 2 V?
EN(H4SO)(diag)-155
ENGINE (DIAGNOSTICS)
Yes
Go to step 2. Go to step 3.
Replace the knock Repair ground
sensor. <Ref. to short circuit in har-
FU(H4SO)-30, ness between
Knock Sensor.> knock sensor con-
nector and ECM
connector.
NOTE:
The harness be-
tween both con-
nectors is shielded.
Repair short circuit
of harness together
with shield.
Even if malfunction Repair poor con-
indicator light tact in ECM con-
lights up, the cir- nector.
cuit has returned
to a normal condi-
tion at this time.
(However, the pos-
sibility of poor con-
tact still remains.)
NOTE:
In this case, repair
the following:
• Poor contact in
knock sensor con-
nector
• Poor contact in
ECM connector
• Poor contact in
coupling connector
No