Subaru 2006 Legacy, Manual

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GD(H4DOTC)-74
Diagnostic Trouble Code (DTC) Detecting Criteria
GENERAL DESCRIPTION
AE: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 CONDITION
3. GENERAL DRIVING CYCLE
Perform the diagnosis continuously at idling or at a constant vehicle speed after warming up the engine.
4. DIAGNOSTIC METHOD
• Abnormality Judgment
Compare the diagnosed value (fsobd) with the threshold value, and if a condition where the malfunction cri-
teria below are met continues for more than 30 seconds, judge that there is a fault in the fuel system.
Time Needed for Diagnosis:
10 seconds × 5 times
Malfunction Indicator Light Illumination: Illuminates when malfunction occurs in 2 continuous driving cy-
cles.
• Normality Judgment
Judge as OK when the malfunction criteria below are completed for 10 seconds or more.
Secondary Parameters Enable Conditions
A/F main learning system In operation
Engine coolant temperature
≥
70°C (158°F)
Engine load
≥
Value from Map 5
Intake air change during 0.5 engine revs.
≤
0.02 g (0.001 oz)/rev
Map 5
Engine speed (rpm) Idling 800 1200 1600 2000 2400 2800 3200 3600 4000 4400
Measured value (g(oz)/
rev) Non-
turbo
0.236
(0.008)
0.232
(0.008)
0.226
(0.008)
0.231
(0.008)
0.252
(0.009)
0.262
(0.009)
0.243
(0.009)
0.243
(0.009)
0.267
(0.009)
0.270
(0.010)
Judgment Value
Malfunction Criteria Threshold Value
fsobd = (sglmd – tglmda) + faf + flaf
≥
fsobdL1
where,
sglmd = measured lambda
tglmda = target lambda
faf = main feedback compensation coef-
ficient every 64 milliseconds
flaf = main feedback learning compensa-
tion coefficient See Map 4
fsobdL1 = lean side
threshold value of
fsobd
Map 4 Threshold value for fuel system malfunction criteria
Amount of air (g(oz)/s) 0(0)
2.3
(0.081)
4.7
(0.166)
7
(0.247)
9.4
(0.332)
11.7
(0.413)
14.1
(0.497)
fsobdL1 (%) 40 40 36.9 32.0 27.0 26.5 26.5
Judgment Value
Malfunction Criteria Threshold Value
fsobd = (sglmd – tglmda) + faf + flaf < 19%
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