Subaru Legacy IV (2008 year). Manual - part 403

GD(H4DOTC)-62

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

• Abnormality Judgement

1) Judge as NG when the judgment value is larger than the threshold value after deceleration fuel cut.
Response time (diagnosis value) > threshold value 

o abnormal

2) If the oxygen sensor voltage is small after recovering from a deceleration fuel cut, and remains small,
judge as NG.

Time Needed for Diagnosis: 1 time(s)
Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cy-
cles.

• Normality Judgement

1) Regardless of a deceleration fuel cut, if the response time (diagnosis value) when the oxygen sensor volt-
age has changed from rich to lean is shorter than the threshold value (judgment value), judge as a normal
condition.
Response time (diagnosis value) 

d threshold value o normal

2) Do not judge as a normal condition.

Judge as OK and clear the NG if the following conditions are established.

Time Needed for Diagnosis: 1 time(s)

Judgement Value

Malfunction Criteria

Threshold Value

Shortest time change from lean (0.3 V 
O

2

 output) to rich (0.5 V) when voltage 

changes from 0.25 V to 0.55 V

> 2000 ms

or

 

Longest time under 0.25 V

t 120000 ms

Judgement Value

Malfunction Criteria

Threshold Value

Shortest time change from lean (0.3 V 
O

2

 output) to rich (0.5 V) when voltage 

changes from 0.25 V to 0.55 V

d 2000 ms

GD(H4DOTC)-63

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

AG:DTC P0140 O2 SENSOR CIRCUIT NO ACTIVITY DETECTED 

(BANK1 SENSOR2)

1. OUTLINE OF DIAGNOSIS

Detect the rear oxygen sensor open or short circuit. Judge as NG when the rear oxygen sensor voltage can
be determined to be abnormal considering conditions such as intake air amount, engine coolant tempera-
ture, main feedback control and deceleration fuel cut.

2. COMPONENT DESCRIPTION

3. ENABLE CONDITION (USED ONLY FOR MALFUNCTION JUDGMENT)

4. GENERAL DRIVING CYCLE

Perform the diagnosis once after starting the engine.

(A)

Electromotive force

(C)

Rich

(E)

Theoretical air fuel ratio

(B)

Air fuel ratio

(D)

Lean

(F)

Comparative voltage

 

 

 

 

 

 

(1)

Atmosphere

(2)

Exhaust gas

(3)

Electromotive force

Secondary Parameters

Enable Conditions

Closed loop control at the rear oxygen 
sensor

In operation

Target output voltage of rear oxygen sen-
sor

t 0.55 V + 0.05 V

Amount of intake air

t 10 g/s (0.35 oz/s)

Engine coolant temperature

t 70 °C (158 °F)

Misfire detection every 200 rotations

< 5 time(s)

Front oxygen (A/F) sensor compensation 
coefficient

Not in limit value

Battery voltage

t 10.9 V

Deceleration fuel cut of 5000 ms or 
more.

Experienced

EN-01696

(3)

V

(1)

(2)

(2)

(E)

(F)

(C)

(B)

(D)

(A)

GD(H4DOTC)-64

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

5. DIAGNOSTIC METHOD

• Abnormality Judgement

If the duration of time while the following conditions are met is longer than the time indicated, judge as NG.

Time Needed for Diagnosis: 200000 ms
Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cy-
cles.

• Normality Judgement

Judge as OK and clear the NG if the following conditions are established.

Judgement Value

Malfunction Criteria

Threshold Value

Minimum output voltage

> 0.15 V

or

 

Maximum output voltage

< 0.55 V

Judgement Value

Malfunction Criteria

Threshold Value

Diagnosis of the rear oxygen sensor volt-
age low side

Incomplete

Minimum output voltage

d 0.15 V

Maximum output voltage

t 0.55 V

GD(H4DOTC)-65

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 CONDITION

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.

Time Needed for Diagnosis: 10 s × 5 time(s)
Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cy-
cles.

• 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.

Time Needed for Diagnosis: 10 s

Secondary Parameters

Enable Conditions

A/F main learning system

In operation

Engine coolant temperature

t 70 °C (158 °F)

Engine load change

< 0.02 g/rev (0 oz/rev)

Engine load

t Value of Map 1

Map1

Engine speed (rpm)

Idling

800

1200

1600

2000

2400

2800

3200

3600

4000

4400

Measured value (g(oz)/rev)

Non-turbo

0.228 

(0.01)

0.22 

(0.01)

0.22 

(0.01)

0.22 

(0.01)

0.228

(0.01)

0.23 

(0.01)

0.234 

(0.01)

0.242 

(0.01)

0.25 

(0.01)

0.25

(0.01)

Judgement Value

Malfunction Criteria

Threshold Value

fsobd = (sglmd – tglmda) + faf + flaf

t Value of Map 2

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)

0 (0)

2.34375 

(0.08)

4.6875 

(0.17)

7.03125 

(0.25)

9.375 

(0.33)

11.71875 

(0.41)

14.0625 

(0.5)

fsobdL1 (%)

1.4

1.4

1.368623

1.319185

1.26975

1.265

1.265

Judgement Value

Malfunction Criteria

Threshold Value

fsobd = (sglmd – tglmda) + faf + flaf

< 1.2