Subaru 2009 IMPREZA Service Manual page 1654

Diagnostic Trouble Code (DTC) Detecting Criteria
GENERAL DESCRIPTION
AH:DTC P0171 SYSTEM TOO LEAN (BANK 1)
1. OUTLINE OF DIAGNOSIS
Detect fuel system malfunction by the amount of main feedback control.
DIAGNOSTIC METHOD
Fuel system is diagnosed by comparing the target air fuel ratio calculated by ECM with the actual air fuel ratio
measured by sensor.
2. ENABLE CONDITIONS
Secondary Parameters
A/F main learning system
Engine coolant temperature
Engine load change
Engine load
Map1
Engine speed (rpm)
Measured value (g(oz)/rev)
3. GENERAL DRIVING CYCLE
Perform the diagnosis continuously at idling or at a constant speed after warming up the engine.
4. DIAGNOSTIC METHOD
• Abnormality Judgement
Compare the diagnosed value (fsobd) with the threshold value, and if a condition meeting the malfunction cri-
teria below continues for 10 s × 5 time(s) or more, judge that there is a fault in the fuel system.
Judgement Value
Malfunction Criteria
fsobd = (sglmd – tglmda) + faf + flaf
In this case: sglmd = measured lambda
tglmda = target lambda
faf = main feedback compensation coef-
ficient every 64 milliseconds
flaf = main feedback learning compensa-
tion coefficient
Map2
Amount of air (g (oz)/s)
fsobdL1 (%)
Time Needed for Diagnosis: 10 s × 5 time(s)
Malfunction Indicator Light Illumination: Illuminates when malfunction occurs in 2 continuous driving cycles.
• Normality Judgement
Judge as OK and clear the NG if the continuous time while the following conditions are established is more
than the predetermined time.
Judgement Value
Malfunction Criteria
fsobd = (sglmd – tglmda) + faf + flaf
Time Needed for Diagnosis: 10 s
Enable Condition
In operation
70 °C (158 °F)
< 0.02 g/rev (0 oz/rev)
Value of Map 1
Idling 800 1200
0.228 0.22
na
(0.01) (0.01)
Threshold Value
Value of Map 2
2.34375 4.6875
0 (0)
(0.08) (0.17)
1.4 1.4 1.368623 1.319185
Threshold Value
< 1.2
GD(H4DOTC)-66
1600 2000 2400 2800
0.22 0.22 0.228 0.23
(0.01) (0.01) (0.01) (0.01)
7.03125 9.375 11.71875
(0.25) (0.33) (0.41)
1.26975 1.265
3200 3600 4000 4400
0.234 0.242 0.25 0.25
(0.01) (0.01) (0.01) (0.01)
14.0625
(0.5)
1.265