Subaru Impreza 2004 Service Manual page 64

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
1 CHECK ANY OTHER DTC ON DISPLAY.
AC:DTC P0171 SYSTEM TOO LEAN (BANK 1)
NOTE:
For the diagnostic procedure, refer to DTC P0172. <Ref. to EN(H4DOTC)(diag)-144, DTC P0172 SYSTEM
TOO RICH (BANK 1), Diagnostic Procedure with Diagnostic Trouble Code (DTC).>
Check
Is any other DTC displayed?
EN(H4DOTC)(diag)-143
ENGINE (DIAGNOSTICS)
Yes
Inspect the rele- Replace the rear
vant DTC using oxygen sensor.
"List of Diagnostic <Ref. to
Trouble Code FU(H4DOTC)-46,
(DTC)". <Ref. to Rear Oxygen Sen-
EN(H4DOTC)(dia sor.>
g)-74, List of Diag-
nostic Trouble
Code (DTC).>
NOTE:
In this case, it is
not necessary to
inspect DTC
P0139.
No