Part 1
2AZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0136-P0139: Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
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 or 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 DTC 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 less than 0.21 V (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 more than 0.59 V (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 1.2 V or more 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.
HINT
- The impedance cannot be measured using an ohmmeter.
- DTC P0136 indicate the deterioration of the HO2 sensor. The ECM sets the DTC by calculating the impedance of the sensor when the typical enabling conditions are satisfied (2 driving cycles).
- DTC P0137 indicate an open or short circuit in the HO2 sensor (2 driving cycles). The ECM sets the DTC 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 for 7 seconds or more, or voltage does not drop from 0.35 V to 0.2 V for 1 second or more, the ECM determines that the sensor response 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 Output Voltage (Abnormal Voltage Output, High Voltage and Low Voltage)::
Heated Oxygen Sensor Impedance (Low):
Heated Oxygen Sensor Impedance (Low)::
Heated Oxygen Sensor Impedance (High):
Heated Oxygen Sensor Impedance (High)::
Heated Oxygen Sensor Output Voltage (Extremely High):
Heated Oxygen Sensor Output Voltage (Extremely High)::
Heated Oxygen Sensor Output Voltage During Fuel Cut:
Heated Oxygen Sensor Output Voltage During Fuel Cut::
TYPICAL MALFUNCTION THRESHOLDS
Heated Oxygen Sensor Output Voltage (Abnormal Voltage Output):
Heated Oxygen Sensor Output Voltage (Abnormal Voltage Output)::
Heated Oxygen Sensor Output Voltage (Low Voltage):
Heated Oxygen Sensor Output Voltage (Low Voltage)::
Heated Oxygen Sensor Output Voltage (High Voltage):
Heated Oxygen Sensor Output Voltage (High Voltage)::
Heated Oxygen Sensor Impedance (Low):
Heated Oxygen Sensor Impedance (Low)::
Heated Oxygen Sensor Impedance (High):
Heated Oxygen Sensor Impedance (High)::
Heated Oxygen Sensor Output Voltage (Extremely High):
Heated Oxygen Sensor Output Voltage (Extremely High)::
Heated Oxygen Sensor Output Voltage During Fuel Cut:
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
P0136, P0137 and P0138
- Connect the Techstream to the DLC3.
- Turn the ignition switch to ON and turn the Techstream on.
- Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure) DTC Check / Clear.
- Turn the ignition switch off.
- Turn the ignition switch to ON and turn the Techstream on [A].
- Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher [B].
- With the transmission in 4th gear or higher, drive the vehicle at 37 to 75 mph (60 to 120 km/h) for 10 minutes or more [C].
- Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
- Input the DTC: P0136, P0137 or P0138.
- Check the DTC judgment result [D].
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
HINT
If the judgment result shows INCOMPLETE or UNKNOWN, perform steps [C] and [D].
- If the test result is UNKNOWN, enter the following menus: Powertrain / Engine and ECT / Trouble Codes / Pending.
- Read Pending DTCs.
HINT
If a pending DTC is output, the system is malfunctioning.
P0139
- Connect the Techstream to the DLC3.
- Turn the ignition switch to ON and turn the Techstream on.
- Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure) DTC Check / Clear.
- Turn the ignition switch off.
- Turn the ignition switch to ON and turn the Techstream on [A].
- Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher [B].
- Drive the vehicle at 37 mph (60 km/h), and then decelerate the vehicle by releasing the accelerator pedal for 7 seconds or more to perform the fuel cut [C].
- Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
- Input the DTC: P0139.
- Check the DTC judgment result [D].
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
HINT
If the judgment result shows INCOMPLETE or UNKNOWN, move the shift lever to 2nd and then perform steps [C] through [D] again.
- If the test result is UNKNOWN, enter the following menus: Powertrain / Engine and ECT / Trouble Codes / Pending.
- Read Pending DTCs.
HINT
If a pending DTC is output, the system is malfunctioning.
INSPECTION PROCEDURE
HINT
Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F Sensor 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 Control the Injection Volume for A/F Sensor operation using the Techstream.
- Connect the Techstream to the DLC3.
- Start the engine and turn the Techstream on.
- Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
- Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
- Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
- Monitor the voltage outputs of the A/F and HO2 sensors (AFS Voltage B1S1 and OS2 B1S2) displayed on the Techstream.
HINT
- The Control the Injection Volume for A/F Sensor 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:
Standard::
NOTICE:
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 Control the Injection Volume for A/F Sensor 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 Techstream: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / A/F Control System / AFS Voltage B1 S1 and O2S B1 S2; then press the graph button on the Data List view.
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 Techstream. 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 Techstream to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn the Techstream on.
(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(e) Read the DTCs.
Result:
D -- READ VALUE USING TECHSTREAM (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)
C -- READ VALUE USING TECHSTREAM (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)
B -- INSPECT FOR EXHAUST GAS LEAK
A -- Continue to next step.
2. READ VALUE USING TECHSTREAM (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn the Techstream on.
(d) Enter the following menus: Powertrain / Engine and ECT / Data List / A/F Control System / O2S B1 S2.
(e) Allow the engine to idle.
(f) Read the Heated Oxygen (HO2) sensor output voltage while idling.
Result:
B -- PERFORM ACTIVE TEST USING TECHSTREAM (INJECTION VOLUME)
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 Removal
OK -- Continue to next step.
4. CHECK HARNESS AND CONNECTOR (CHECK FOR SHORT)
(a) Turn the ignition switch 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 Removal