DTC P0133: O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)

OUTLINE OF DIAGNOSIS
Detect the slow response of front oxygen (A/F) sensor.

Front oxygen (A/F) sensor cover has some ventilation holes for exhaust gas. Clogged ventilation holes are diagnosed.

When the holes are clogged, the A/F output variation becomes slow comparing with the actual A/F variation because oxygen which reaches the zirconia layer is insufficient. Therefore, if the cover has clogged holes, the rich to lean judgment in ECM is delayed when the change from rich to lean is caused.

Fig 1: Identifying A/F Sensor Cloging
Courtesy of SUBARU OF AMERICA, INC.

When abnormal, the variation period from rich to lean is longer than when normal, as shown in the figure below.

When the condition is completed, the variation time from rich to lean and vice versa is calculated by varying the desired A/F value. Judge NG when the period is long.

Fig 2: Air Fuel Ration Malfunction Graph
Courtesy of SUBARU OF AMERICA, INC.
COMPONENT DESCRIPTION

Fig 3: A/F Sensor Cross Sectional View And Air Fuel Ratio Graph
Courtesy of SUBARU OF AMERICA, INC.

ENABLE CONDITION

ENABLE CONDITIONS

Secondary Parameter	Enable Condition
Closed loop control	In operation
Average lambda	0.703 <--> 1.375
After starting the engine	225 seconds or more
Engine coolant temperature	"GREATER THAN EQUAL TO" 75°C (167°F)
Injector pulse	1.792 <--> 4.032 milliseconds
Engine speed	1800 <--> 3000 rpm
Vehicle speed	"GREATER THAN EQUAL TO" 76 km/h (47 MPH)
Atmospheric air pressure	"GREATER THAN EQUAL TO" 76 kPa (568 mmHg, 22 inHg)
Throttle position change for 90 milliseconds	< 1.60°
Impedance of lambda sensor	10 <--> 40 Ω
Misfire rate at engine 200 rev.	"LESS THAN EQUAL TO" 1.0%

GENERAL DRIVING CYCLE
Perform diagnosis constantly more than 76 km/h (47 MPH) just once in 225 seconds after starting the engine.

DIAGNOSTIC METHOD

When enable conditions are completed, measure the A/F sensor output A/F value variation period by changing air fuel ratio desired value to lean and rich. Judge NG when this period is long. Judge OK when this period is short.

Judge NG when the malfunction criteria below is completed. Judge OK when the malfunction criteria below is not completed.

Judgment Value

JUDGMENT VALUE

Malfunction Criteria	Threshold Value
Average time of 5 changes from rich to lean, and from lean to rich	> See Map 5
Response time when noise is detected is not used as data.

Map 5

VEHICLE SPEED AND A/F SENSOR OUTPUT A/F VALUE SPECIFICATIONS

Engine Speed (Ne) (rpm)	1.75 "LESS THAN EQUAL TO" TP < 2.25 (milliseconds)	2.25 "LESS THAN EQUAL TO" TP < 2.75 (milliseconds)	2.75 "LESS THAN EQUAL TO" TP < 3.19 (milliseconds)	3.19 "LESS THAN EQUAL TO" TP (milliseconds)
"LESS THAN EQUAL TO" Ne <	1898	1731	1658	1591
"LESS THAN EQUAL TO" Ne < 2,500	1720	1570	1540	1530
2,500 "LESS THAN EQUAL TO" Ne < 3,000	1674	1535	1499	1478
3,000 "LESS THAN EQUAL TO" Ne	1674	1535	1499	1478

Time Needed for Diagnosis: 2 to 12 seconds

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

DTC CLEAR CONDITION
- When the OK idling cycle was completed 40 times in a row
- When "Clear Memory" was performed
MALFUNCTION INDICATOR LIGHT CLEAR CONDITION
- When the OK driving cycle was completed 3 times in a row
- When "Clear Memory" was performed
FAIL SAFE
None
ECM OPERATION AT DTC SETTING
- Memorize the freeze frame data. (For test mode $02)
- Memorize the diagnostic value and trouble standard value. (For test mode $06)