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Home >> Subaru >> 2005 >> Forester XT, Automatic >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Diagnostic Trouble Code (DTC) Detecting Criteria (H4DOTC) >> Diagnostic Trouble Code (DTC) Detecting Criteria >> DTC P0171 System Too Lean (Bank 1) >> Diagnostic Method
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Diagnostic Method

Judge that the fuel system malfunction occurs when the time during completing the malfunction criteria below continues 30 seconds or more by comparing the diagnosed value (fsobd) with threshold value.

Judgment Value 

JUDGMENT VALUE

Malfunction Criteria Threshold Value
fsobd = (sglmd - tglmda) + faf + flaf where,
sglmd = measured lambda
>/= fsobdL1
See THRESHOLD VALUE FUEL SYSTEM MALFUNCTION CRITERIA SPECIFICATION 
tglmda = target lambda fsobdL1 = lean side threshold value of fsobd
faf = main feedback compensation coefficient every 64 milliseconds  
flaf = main feedback learning compensation coefficient  

Map 4 Threshold value for fuel system malfunction criteria 

THRESHOLD VALUE FUEL SYSTEM MALFUNCTION CRITERIA SPECIFICATION

Amount of air (g/s) 0 2.4 4.7 7 9.4 11.7 14.1
fsobdL1 (%) 40 40 36.9 32.0 27.0 26.5 26.5

Time Needed for Diagnosis:  10 seconds x 5 times

Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cycles.

Judge OK when the malfunction criteria below are continued for 10 seconds.

Judgment Value 

JUDGMENT VALUE

Malfunction Criteria Threshold Value
fsobd = (sglmd - tglmda) + faf + flaf < 19%