Subaru Legacy IV (2008 year). Manual - part 402

 

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Subaru Legacy IV (2008 year). Manual - part 402

 

 

GD(H4DOTC)-58

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

AF:DTC P0139 O2 SENSOR CIRCUIT SLOW RESPONSE (BANK 1 SENSOR 2)

1. OUTLINE OF DIAGNOSIS

Detect the slow response of the oxygen sensor.
Judge as NG if either the rich to lean response diagnosis or lean to rich response diagnosis is NG, and Judge
as OK if both are OK.
[Rich

o lean diagnosis response]

1. Measure the response time for oxygen sensor output changes when the A/F ratio changes to rich to lean.
If the measured response time is larger than the threshold value, it is NG. If it is smaller, it is OK.
2. Judge as NG when the oxygen sensor voltage is large (rich) when recovering from a deceleration fuel cut.
[Lean 

o rich diagnosis response]

1. Measure the response time for oxygen sensor output changes when the A/F ratio changes to lean to rich.
If the measured response time is larger than the threshold value, it is NG.
2. Judge as NG when the oxygen sensor voltage remains small when recovering from a deceleration fuel cut.

DIAGNOSTIC METHOD

Measure the response time of the output change of the oxygen sensor when the A/F ratio changes to rich to
lean. And Judge as NG when the measured response time is larger than the threshold value.

2. COMPONENT DESCRIPTION

3. ENABLE CONDITION

Rich

o lean diagnosis response

(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

Battery voltage

t 10.9 V

A/F main feedback control condition

Completed

Deceleration fuel cut time is 5000 ms or more.

Experienced

After fuel cut

t 2000 ms

Current calculation time of the rear oxygen sensor heater

t 60000 ms

Current continuation time of the rear oxygen sensor heater

t 30000 ms

Estimated catalyst temperature

t 400 °C (752 °F)

Number of deceleration fuel cut

t 1 time(s)

EN-01696

(3)

V

(1)

(2)

(2)

(E)

(F)

(C)

(B)

(D)

(A)

GD(H4DOTC)-59

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

4. GENERAL DRIVING CYCLE

Perform the diagnosis only once when deceleration fuel cut occurs after rapid acceleration. (Pay attention to
the oxygen sensor voltage for the timing of the deceleration.)

5. DIAGNOSTIC METHOD

When the oxygen sensor output voltage changes from 0.55 V (rich) to 0.15 V (lean), calculate the minimum
response time for output change between 0.5 V and 0.2 V for the judgment criteria.

(A)

0.55 V

(E)

0 V

(H)

Execute the malfunction judg-
ment in 2000 ms from the recov-
ery of fuel cut on deceleration.

(B)

0.5 V

(F)

More than 5000 ms

(C)

0.2 V

(G)

Measure the response time.

 

(D)

0.15 V

(A)

(B)

(C)

(D)

(E)

Diagnosis execution condition

Rear oxygen sensor (V)

(G)

Fuel cut on deceleration

(F)

(H)

EN-05566

GD(H4DOTC)-60

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

NOTE:
Variation time of rear oxygen sensor output voltage is short during fuel cut in deceleration. NG judgment
should be performed after deceleration fuel cut. Even without deceleration fuel cut, judge as OK if the value
is below the threshold.
When the deceleration fuel cut time is 5000 ms or more, judge as NG if the following criteria are met 2000
ms after recovering from the deceleration fuel cut.
2) Judge as NG when the oxygen sensor voltage at recovery from a deceleration fuel cut, is large.
If the fuel cut time in a deceleration fuel cut is long (5000 ms or more), and even after recovering from a de-
celeration fuel cut, the oxygen sensor voltage is high (0.55 V or more), 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)

6. ENABLE CONDITION

Lean 

o rich response diagnosis

Judgement Value

Malfunction Criteria

Threshold Value

Shortest time change from rich (0.5 V O

2

output) to lean (0.2 V) when voltage 
reduces from 0.55 V to 0.15 V

> 837 ms

or

 

Longest time over 0.55 V

t 2000 ms

Judgement Value

Malfunction Criteria

Threshold Value

Shortest time change from rich (0.5 V O

2

output) to lean (0.2 V) when voltage 
reduces from 0.55 V to 0.15 V

d 837 ms

Secondary Parameters

Enable Conditions

Battery voltage

t 10.9 V

A/F main feedback control condition

Completed

Deceleration fuel cut time is 6000 ms or 
more.

Experienced

After fuel cut

t 2000 ms

Current calculation time of the rear oxy-
gen sensor heater

t 0 ms

Current continuation time of the rear oxy-
gen sensor heater

t 0 ms

Estimated catalyst temperature

t 0 °C (32 °F)

Number of deceleration fuel cut

t 1 time(s)

GD(H4DOTC)-61

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

7. GENERAL DRIVING CYCLE

Perform the diagnosis only once when deceleration fuel cut occurs after rapid acceleration. (Pay attention to
the oxygen sensor voltage for the timing of the deceleration.)

8. DIAGNOSTIC METHOD

When the oxygen sensor output voltage changes from 0.25 V (lean) to 0.55 V (rich), calculate the minimum
response time for output change between 0.3 V and 0.5 V for the judgment criteria.

(A)

0.55 V

(G)

More than 120000 ms

(J)

Judge NG when the voltage of 
rear oxygen sensor is 0.25 V or 
less for 120000 ms or more after 
recovery of fuel cut on decelera-
tion.

(B)

0.5 V

(H)

Measure the response time (diag-
nostic value).

(C)

0.3 V

(D)

0.25 V

(I)

Execute the malfunction judg-
ment in 2000 ms from the recov-
ery of fuel cut on deceleration.

(E)

0 V

(F)

More than 5 seconds

(I)

(E)

(F)

(G)

(D)

(C)

(B)

(A)

(H)

(J)

EN-05567

Diagnosis execution condition

Rear oxygen sensor (V)

Fuel cut on deceleration

 

 

 

 

 

 

 

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