Subaru 2009 IMPREZA Service Manual page 588

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
1 CHECK FOR ANY OTHER DTC ON DISPLAY. Is any other DTC displayed?
Check
EN(H4SO)(diag)-171
ENGINE (DIAGNOSTICS)
Yes No
Check the appro- Replace the oil
priate DTC using temperature sen-
the "List of Diag- sor. <Ref. to
nostic Trouble FU(H4SO)-40, Oil
Code (DTC)". Temperature Sen-
<Ref. to sor.>
EN(H4SO)(diag)-
86, List of Diagnos-
tic Trouble Code
(DTC).>