Subaru IMPREZA 2002 Service Manual page 478

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
ENGINE (DIAGNOSTICS)
AA:DTC PO171
-
FUEL TRIM MALFUNCTION ( N F TOO LEAN)
-
Refer to DTC PO172 for diagnostic procedure. <Ref. to EN(S0HC)-154, DTC PO172
-
FUEL TRIM MAL-
FUNCTION ( N F TOO RICH)
-,
Diagnostic Procedure with Diagnostic Trouble Code (DTC).>
AB:DTC PO172
-
FUEL TRIM MALFUNCTION ( N F TOO RICH)
-
DTC DETECTING CONDITION:
Two consecutive driving cycles with fault
TROUBLE SYMPTOM:
Erroneous idling
Engine stalls.
Poor driving performance
CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(S0HC)-43, OP-
ERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(S0HC)-40, OPERATION, Inspec-
tion Mode.>.
Yes
3epair exhaust
jystem.
3epair air intake
system.
30 to step 4.
Step
CHECK EXHAUST SYSTEM.
No
Go to step 2.
Go to step
3.
Repair the follow-
ing items.
Fuel pressure too
high
Clogged fuel
return line or
bent hose
Fuel pressure too
low
Improper fuel
pump discharge
Clogged fuel
supply line
CHECK AIR INTAKE SYSTEM.
CHECK FUEL PRESSURE.
Warning:
*Place "NO FIRE" signs near the working
area.
*Be careful not to spill fuel on the floor.
1)Release fuel pressure.
(1) Disconnect the connector from fuel
pump relay.
(2) Start the engine and run it until it stalls.
(3) After the engine stalls, crank it for five
more seconds.
(4) Turn the ignition switch to OFF.
2)Connect the connector to fuel pump relay.
3)Disconnect the fuel delivery hose from fuel
filter, and connect fuel pressure gauge.
4)lnstall the fuel filler cap.
5)Start the engine and idle while gear position
is neutral.
6)Measure the fuel pressure while disconnect-
ing pressure regulator vacuum hose from
intake manifold.
Warning:
Before removing the fuel pressure gauge,
release fuel pressure.
NOTE:
If fuel pressure does not increase, squeeze fuel
return hose 2 to 3 times, then measure fuel
Dressure aaain.
Check
ire there holes or loose bolts
)n exhaust system?
ire there holes, loose bolts or
lisconnection of hose on air
ntake system?
s fuel pressure between 284
ind 314 kPa (2.9
-
3.2 kgl
:m2, 41
-
46 psi)?
EN(S0HC)-154