DTC P0139: O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)

Detect the slow response of rear oxygen sensor.

Calculate the response time of the output change of the rear oxygen sensor when the A/F ratio changes from rich to lean. And carry out the diagnosis comparing the calculated response time with the threshold value.

Fig 1: Rear Oxygen Sensor Slow Response Outline Diagram

Courtesy of SUBARU OF AMERICA, INC.

Diagnosis is performed only once when the deceleration fuel is cut from the rapid acceleration. (Pay attention to oxygen sensor voltage to calculate the diagnostic value when deciding the deceleration timing.)

When the rear oxygen sensor output voltage changes from 0.5 V (rich) to 0.15 V (lean), carry out calculation regarding the response time of the output change from 0.45 V to 0.2 V as diagnostic value. When the rear oxygen sensor output voltage does not change from 0.5 V to 0.15 V, do not carry out calculation even if the output changes from 0.45 V to 0.2 V.

• Abnormality Judgment 

  Judge NG when the rear oxygen sensor output change response time (diagnostic value) exceeds the threshold value.

  Response time > 2 seconds (threshold value) --> Abnormal

  Judge NG when all of the malfunction criteria below is completed.

  Judgment Value 

  JUDGMENT VALUE (ABNORMALITY JUDGMENT)
  
  

  Malfunction Criteria	Threshold Value
  Shortest time change from rich (450 mV oxygen output) to lean (200 mV) if voltage reduces from 500 mV to 150 mV	"LESS THAN EQUAL TO" 0.43 seconds
  2 seconds or more fuel shut-off in decel.	Experienced
  After fuel shut-off	2 seconds or more

  Time Needed for Diagnosis:  4 seconds

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

• Normality Judgment 

  Judge OK when the rear oxygen sensor output change response time (diagnostic value) is below the threshold value.

  Response time "LESS THAN EQUAL TO" 2 seconds (threshold value) --> Normal

  Judge NG when the malfunction criteria below is completed.

  Judgment Value 

  JUDGMENT VALUE (NORMALITY JUDGMENT)
  
  

  Malfunction Criteria	Threshold Value
  Shortest time change	"LESS THAN EQUAL TO" 0.43 seconds

  NOTE: Response time is calculated during the deceleration fuel cut in case of abnormal judgment. However, in order to make a normal judgment quickly, diagnosis is performed without deceleration fuel cut.
  Fig 3: Rear Oxygen Sensor Output Voltage Graph

  Courtesy of SUBARU OF AMERICA, INC.

• When the OK idling cycle was completed 40 times in a row
• When "Clear Memory" was performed

• When the OK driving cycle was completed 3 times in a row
• When "Clear Memory" was performed

None

• Memorize the freeze frame data. (For test mode $02)
• Memorize the diagnostic value and trouble standard value. (For test mode $06)