P0136
2AZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0136: Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
DTC P0136 - Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
DTC P0137 - Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2)
DTC P0138 - Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2)
DTC P0139 - Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 2)
DESCRIPTION
A three-way catalytic converter (TWC) is used in order to convert the carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) into less harmful substances. To allow the TWC to function effectively, it is necessary to keep the air-fuel ratio of the engine near the stoichiometric air-fuel ratio. For the purpose of helping the ECM to deliver accurate air-fuel ratio control, the Heated Oxygen (HO2) sensor is used.
The HO2 sensor is located behind the TWC, and detects the oxygen concentration in the exhaust gas. Since the sensor is integrated with the heater that heats the sensing portion, it is possible to detect the oxygen concentration even when the intake air volume is low (the exhaust gas temperature is low).
When the air-fuel ratio becomes lean, the oxygen concentration in the exhaust gas is rich. The HO2 sensor informs the ECM that the post-TWC air-fuel ratio is lean (low voltage, i.e. less than 0.45 V).
Conversely, when the air-fuel ratio is richer than the stoichiometric air-fuel level, the oxygen concentration in the exhaust gas becomes lean. The HO2 sensor informs the ECM that the post-TWC air-fuel ratio is rich (high voltage, i.e. more than 0.45 V). The HO2 sensor has the property of changing its output voltage drastically when the air-fuel ratio is close to the stoichiometric level.
The ECM uses the supplementary information from the HO2 sensor to determine whether the air-fuel ratio after the TWC is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the HO2 sensor is working improperly due to internal malfunctions, the ECM is unable to compensate for deviations in the primary air-fuel ratio control.
HINT: Sensor 2 refers to the sensor mounted behind the Three-Way Catalytic Converter (TWC) and located far from the engine assembly.
MONITOR DESCRIPTION
1. Active Air-Fuel Ratio Control
The ECM usually performs air-fuel ratio feedback control so that the Air-Fuel Ratio (A/F) sensor output indicates a near stoichiometric air-fuel level. This vehicle includes active air-fuel ratio control in addition to regular air-fuel ratio control. The ECM performs active air-fuel ratio control to detect any deterioration in the Three-Way Catalytic Converter (TWC) and Heated Oxygen (HO2) sensor malfunctions (refer to the diagram below).
Active air-fuel ratio control is performed for approximately 15 to 20 seconds while driving with a warm engine. During active air-fuel ratio control, the air-fuel ratio is forcibly regulated to become lean or rich by the ECM. If the ECM detects a malfunction, a DTC is set.
2. Abnormal Voltage Output of Heated Oxygen (HO2) Sensor (DTC P0136)
While the ECM is performing active air-fuel ratio control, the air-fuel ratio is forcibly regulated to become rich or lean. If the sensor is not functioning properly, the voltage output variation is small. For example, when the HO2 sensor voltage does not decrease to less than 0.21 V and does not increase to more than 0.59 V during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormal and sets DTCs P0136.
3. Open or Short in Heated Oxygen (HO2) Sensor Circuit (DTCs P0137 or P0138)
During active air-fuel ratio control, the ECM calculates the Oxygen Storage Capacity (OSC)* of the Three-Way Catalytic Converter (TWC) by forcibly regulating the air-fuel ratio to become rich or lean.
If the HO2 sensor has an open or short, or the voltage output of the sensor noticeably decreases, the OSC indicates an extraordinarily high value. Even if the ECM attempts to continue regulating the air-fuel ratio to become rich or lean, the HO2 sensor output does not change.
While performing active air-fuel ratio control, when the target air-fuel ratio is rich and the HO2 sensor voltage output is 0.21 V or less (lean), the ECM interprets this as an abnormally low sensor output voltage and sets DTC P0137. When the target air-fuel ratio is lean and the voltage output is 0.59 V or more (rich) during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormally high, and sets DTC P0138.
HINT: DTC P0138 is also set if the HO2 sensor voltage output is more than 1.2 V for 10 seconds or more.
*: The TWC has the capability to store oxygen. The OSC and the emission purification capacity of the TWC are mutually related. The ECM determines whether the catalyst has deteriorated, based on the calculated OSC value P0420.
4. High or Low Impedance of Heated Oxygen (HO2) Sensor (DTCs P0136 or P0137)
During normal air-fuel ratio feedback control, there are small variations in the exhaust gas oxygen concentration. In order to continuously monitor the slight variation of the HO2 sensor signal while the engine is running, the impedance* of the sensor is measured by the ECM. The ECM determines that there is a malfunction in the sensor when the measured impedance deviates from the standard range.
*: The effective resistance in an alternating current electrical circuit.
- The impedance cannot be measured using an ohmmeter.
- DTCs P0136 indicate the deterioration of the HO2 sensor. The ECM sets the DTCs by calculating the impedance of the sensor when the typical enabling conditions are satisfied (2 driving cycles).
- DTCs P0137 indicate an open or short circuit in the HO2 sensor (2 driving cycles). The ECM sets the DTCs when the impedance of the sensor exceeds the threshold 15 kOhms.
5. Abnormal Voltage Output of Heated Oxygen (HO2) Sensor During Fuel-cut (DTC P0139)
The sensor output voltage drops to below 0.2 V (extremely Lean status) immediately when the vehicle decelerates and fuel cut is operating. If the voltage does not drop to below 0.2 V, the ECM determines that the sensor's response feature has deteriorated, illuminates the MIL and sets a DTC.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
Heated Oxygen Sensor Output Voltage (Abnormal Voltage Output, High Voltage and Low Voltage):
Heated Oxygen Sensor Impedance (Low):
Heated Oxygen Sensor Impedance (High):
Heated Oxygen Sensor Output Voltage (Extremely High):
Heated Oxygen Sensor Output Voltage (During fuel cut ):
TYPICAL MALFUNCTION THRESHOLDS
Heated Oxygen Sensor Output Voltage (Abnormal Voltage Output):
Heated Oxygen Sensor Output Voltage (Low):
Heated Oxygen Sensor Output Voltage (High):
Heated Oxygen Sensor Impedance (Low):
Heated Oxygen Sensor Impedance (High):
Heated Oxygen Sensor Output Voltage (Extremely High):
Heated Oxygen Sensor Output Voltage (During fuel cut ):
COMPONENT OPERATING RANGE
MONITOR RESULT
Refer to CHECKING MONITOR STATUS Mode 6 Data.
WIRING DIAGRAM
CONFIRMATION DRIVING PATTERN
HINT:
- This confirmation driving pattern is used in the "PERFORM CONFIRMATION DRIVING PATTERN" procedure of the following diagnostic troubleshooting procedure.
- Performing this confirmation driving pattern will activate the Heated Oxygen (HO2) sensor monitor (The catalyst monitor is performed simultaneously). This is very useful for verifying the completion of a repair.
1. Connect an intelligent tester or a Techstream to the DLC3.
2. Turn the ignition switch to the ON position.
3. Warm-up the engine until the engine coolant temperature reaches 75°C (167°F) or more [A].
4. Drive the vehicle at between 40 mph and 75 mph (60 km/h and 120 km/h) for at least 10 minutes [B].
5. Drive the vehicle at 40 mph (60 km/h) or more and decelerate the vehicle for 8 seconds or more. Perform this 3 times [C].
6. Turn the tester on.
7. Select the following menu items: DIAGNOSIS / ENHANCED OBD II / MONITOR INFO / ALL READINESS.
8. Input DTCs: P0136, P0137, P0138 and P0139.
- Check that DTC MONITOR is "PASS DTC not set." If DTC MONITOR is "Unavailable," perform the drive pattern increasing the vehicle speed and using the second gear to decelerate the vehicle.
INSPECTION PROCEDURE
HINT: Malfunctioning areas can be identified by performing the A/F CONTROL function provided in the ACTIVE TEST. The A/F CONTROL function can help to determine whether the Air-Fuel Ratio (A/F) sensor, Heated Oxygen (HO2) sensor and other potential trouble areas are malfunctioning.
The following instructions describe how to conduct the A/F CONTROL operation using the intelligent tester.
1. Connect the intelligent tester to the DLC3.
2. Start the engine and turn the tester on.
3. Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
4. On the tester, select the following menu items: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL.
5. Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
6. Monitor the voltage outputs of the A/F and HO2 sensors (AFS B1S1 and OS2 B1S2) displayed on the tester.
HINT:
- The A/F CONTROL operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
- Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
Standard:
NOTE: The Air-Fuel Ratio (A/F) sensor has an output delay of a few seconds and the Heated Oxygen (HO2) sensor has a maximum output delay of approximately 20 seconds.
- Following the A/F CONTROL procedure enables technicians to check and graph the voltage outputs of both the A/F and HO2 sensors.
- To display the graph, select the following menu items on the tester: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL / USER DATA / AFS B1S1 and O2S B1S2, and press the YES button and then the ENTER button followed by the F4 button.
HINT:
- If other DTCs relating to different systems that have terminal E2 as the ground terminal are output simultaneously, terminal E2 may have an open circuit.
- Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air-fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
- If the OX1B wire from the ECM connector is short-circuited to the +B wire, DTC P0136 will be set.
PROCEDURE
1. READ DTC OUTPUT (DTC P0136, P0137, P0138 OR P0139)
(a) Connect the intelligent tester to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn the tester ON.
(d) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT CODES.
(e) Read the DTCs.
Result:
C -- READ VALUE USING INTELLIGENT TESTER (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)
B -- INSPECT FOR EXHAUST GAS LEAK
A -- Continue to next step.
2. READ VALUE USING INTELLIGENT TESTER (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)
(a) Connect the intelligent tester to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn the tester ON.
(d) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / PRIMARY / O2S B1 S2.
(e) Allow the engine to idle.
(f) Read the Heated Oxygen (HO2) sensor output voltage while idling.
Result:
B -- INSPECT AIR FUEL RATIO SENSOR
A -- Continue to next step.
3. CHECK HEATED OXYGEN SENSOR (CHECK FOR SHORT)
(a) Disconnect the heated oxygen sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
(c) Reconnect the heated oxygen sensor connector.
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
4. CHECK HARNESS AND CONNECTOR (CHECK FOR SHORT)
(a) Turn the ignition switch to OFF and wait for 5 minutes or more.
(b) Disconnect the ECM connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard resistance:
(d) Reconnect the ECM connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE ECM
5. INSPECT AIR FUEL RATIO SENSOR
HINT: This A/F sensor test is to check the A/F sensor current during the fuel-cut. When the sensor is normal, the sensor current will indicate below 3.0 mA in this test.
(a) Connect the intelligent tester to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn the tester ON.
(d) Drive the vehicle according to the drive pattern listed below:
(1) Warm up the engine until the engine coolant temperature reaches 75°C (167°F) or more.
(2) Drive the vehicle at 60 km/h (40 mph) or more and decelerate the vehicle for 5 seconds or more.
(3) Repeat the deceleration above at least 3 times.
(e) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / MONITOR INFO / MONITOR RESULT.
(f) Confirm that RANGE B1S1 is either PASS or FAIL. If the tester shows INCMP, re-check RANGE B1S1 after performing the drive pattern.
(g) Select the RANGE B1S1.
(h) Read the TEST VALUE.
Standard current:
Less than 3.0 mA
HINT: If the tester shows INCMP again, increase the vehicle speed and use the second gear to decelerate the vehicle. Refer to the CONFIRMATION DRIVING PATTERN.
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- REPLACE HEATED OXYGEN SENSOR
6. READ VALUE USING INTELLIGENT TESTER (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)
(a) Connect the intelligent tester to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn the tester ON.
(d) Start the engine.
(e) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / A/F CONTROL SYS / O2S B1 S2.
(f) After warming up the engine, run the engine at an engine speed of 2500 rpm for 3 minutes.
(g) Read the output voltage of the heated oxygen sensor when the engine rpm is suddenly increased.
HINT: Quickly accelerate the engine to 4000 rpm 3 times using the accelerator pedal.
Standard:
Fluctuates between 0.4 V or less and 0.5 V or more.
NG -- INSPECT FOR EXHAUST GAS LEAK
OK -- Continue to next step.
7. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (INJECTION VOLUME)
(a) Connect the intelligent tester to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn the tester ON.
(d) Start the engine and warm it up.
(e) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / INJ VOL.
(f) Change the fuel injection volume using the tester, and monitor the voltage output of Air Fuel Ratio (A/F) and Heated Oxygen (HO2) sensors displayed on the tester.
HINT:
- Change the fuel injection volume within the range of -12% and +12%. The injection volume can be changed in 1% graduations within the range.
- The A/F sensor is displayed as AFS B1 S1 or AFS B2 S1, and the HO2 sensor is displayed as O2S B1 S2 or O2S B2 S2 on the intelligent tester or Techstream.
Result:
HINT: A normal HO2 sensor voltage (O2S B1 S2) reacts in accordance with increases and decreases in fuel injection volumes. When the A/F sensor voltage remains at either less or more than 3.3 V despite the HO2 sensor indicating a normal reaction, the A/F sensor is malfunctioning.
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- CHECK ENGINE TO DETERMINE CAUSE OF EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO
8. INSPECT FOR EXHAUST GAS LEAK
OK:
No gas leak.
NG -- REPAIR OR REPLACE EXHAUST GAS LEAK POINT
OK -- Continue to next step.
9. INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE)
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
10. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - ECM)
(a) Disconnect the heated oxygen sensor connector.
(b) Disconnect the ECM connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Standard resistance (Check for short):
(d) Reconnect the heated oxygen sensor connector.
(e) Reconnect the ECM connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
11. REPLACE HEATED OXYGEN SENSOR
(a) Replace the heated oxygen sensor Removal.
NEXT -- Continue to next step.
12. PERFORM CONFIRMATION DRIVING PATTERN
HINT: Refer to the CONFIRMATION DRIVING PATTERN.
NEXT -- Continue to next step.
13. CHECK WHETHER DTC OUTPUT RECURS (DTC P0136, P0137, P0138, OR P0139)
(a) Connect the intelligent tester to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn the tester ON.
(d) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / MONITOR INFO / ALL READINESS.
(e) Input DTCs: P0136, P0137, P0138 and P0139.
(1) Intelligent tester - Check that DTC MONITOR is "PASS DTC not set". If DTC MONITOR is "Unavailable", perform the drive pattern increasing the vehicle speed and using the second gear to decelerate the vehicle.
Result:
B -- REPLACE AIR FUEL RATIO SENSOR
A -- END
14. REPLACE AIR FUEL RATIO SENSOR
(a) Replace the air fuel ratio sensor Removal.
NEXT -- Continue to next step.
15. PERFORM CONFIRMATION DRIVING PATTERN
HINT: Refer to CONFIRMATION DRIVING PATTERN.
NEXT -- Continue to next step.
16. CHECK WHETHER DTC OUTPUT RECURS (DTC P0136, P0137, P0138 OR P0139)
(a) Connect the intelligent tester to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn the tester ON.
(d) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / MONITOR INFO / ALL READINESS.
(e) Input DTCs: P0136, P0137, P0138 and P0139.
(1) Intelligent tester - Check that DTC MONITOR is "PASS DTC not set". If DTC MONITOR is "Unavailable", perform the drive pattern increasing the vehicle speed and using the second gear to decelerate the vehicle.
Result:
B -- REPLACE HEATED OXYGEN SENSOR
A -- END