Subaru LEGACY 2003 Service Manual page 87

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
1 CHECK SPEEDOMETER OPERATION IN
COMBINATION METER.
Does speedometer operate normally?
2 CHECK INPUT SIGNAL FOR ECM.
1) Lift-up the vehicle.
2) Set the positive (+) terminal and earth lead
of oscilloscope at ECM connector terminals
and chassis ground.
Connector & terminal
(B135) No. 24 (+) — Chassis ground (–):
3) Start the engine.
4) Shift on the gear position, and put the vehi-
cle at constant speed.
5) Measure signal voltage indicated on oscillo-
scope.
Does the measured value exceed the spec-
ified value?
3 CHECK POOR CONTACT.
Check poor contact in ECM connector.
Is there poor contact in ECM connector?
4 CHECK HARNESS BETWEEN ECM AND
COMBINATION METER CONNECTOR.
Measure voltage between ECM and chassis
ground.
Connector & terminal
(B135) No. 24 (+) — Chassis ground ( − − − − ):
Does the measured value exceed the specified
value?
5 CHECK HARNESS BETWEEN ECM AND
COMBINATION METER CONNECTOR.
1) Turn ignition switch to OFF.
2) Measure resistance of harness between
ECM connector and chassis ground.
Connector & terminal
(B135) No. 24 — Chassis ground:
Is the measured value less than the speci-
fied value?
6 CHECK POOR CONTACT.
Check poor contact in ECM connector.
Is there poor contact in ECM connector?
Value
Speedometer operates nor-
mally.
3 V
There is poor contact.
2 V
10 Ω
There is poor contact.
EN(H4SOw/oOBD)-85
ENGINE (DIAGNOSTICS)
Yes
Go to step 2. Check speedome-
ter and vehicle
speed sensor.
Go to step 3. Go to step 4.
Repair poor con- Replace ECM.
tact in ECM. <Ref. to
FU(H4SOw/
oOBD)-42, Engine
Control Module.>
Repair harness Go to step 5.
and connector.
NOTE:
In this case, repair
the following:
Battery short cir-
cuit in harness
between ECM and
combination meter
connector
Repair ground Go to step 6.
short circuit in har-
ness between
ECM and combi-
nation meter con-
nector.
Repair poor con- Replace ECM.
tact in ECM. <Ref. to
FU(H4SOw/
oOBD)-42, Engine
Control Module.>
No