Part 1
2TR-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0136-P0139: Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
CAUTION / NOTICE / HINT
HINT
Sensor 2 refers to the sensor mounted behind the Three-Way Catalytic Converter (TWC) and located far from the engine assembly.
DESCRIPTION
In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) components in the exhaust gas, a TWC is used. For the most efficient use of the TWC, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel level. For the purpose of helping the ECM to deliver accurate air-fuel ratio control, a 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.
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, one of the following DTCs is set: DTC P0136 (abnormal voltage output), P0137 (open circuit) and P0138 (short circuit).
1. Abnormal Voltage Output of 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.
1. Open or Short in Heated Oxygen (HO2) Sensor Circuit (DTC 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.
1. High or Low Impedance of Heated Oxygen (HO2) Sensor (DTC 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 indicates 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 (1 driving cycle).
- DTC P0137 indicates an open or short circuit in the HO2 sensor (1 driving cycle). The ECM sets the DTC when the impedance of the sensor exceeds the threshold 15 kOhms.
1. HO2 sensor output voltage during fuel cut (P0139)
* The sensor output voltage drops below 0.2 V (extremely lean status) immediately when the vehicle decelerates and fuel cut is operating. If the voltage does not drop below 0.2 V for 7 seconds or voltage does not drop from 0.35 V to 0.2 V for 1 second the ECM determines that the sensor response feature has deteriorated, illuminates the MIL and sets a DTC.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
All:
Heated Oxygen Sensor Output Voltage (Output Voltage, 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 Voltage During fuel-cut:
TYPICAL MALFUNCTION THRESHOLDS
Heated Oxygen Sensor Output Voltage (Output voltage):
Heated Oxygen Sensor Output Voltage (Low output voltage):
Heated Oxygen Sensor Output Voltage (High output voltage):
Heated Oxygen Sensor Impedance (Low):
Heated Oxygen Sensor Impedance (High):
Heated Oxygen Sensor Impedance (Extremely High):
Heated Oxygen Sensor 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
1. Clear the DTCs (even if no DTCs are stored, perform the clear DTC operation) [A].
2. Turn the ignition switch off and wait for at least 30 seconds.
3. Start the engine and warm it up until the ECT reaches 75°C (167°F) or higher [B].
4. With the transmission in 4th gear or higher, drive the vehicle at 40 to 75 mph (60 to 120 km/h) for 10 minutes or more [C].
5. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
6. Input DTCs: P0136, P0137 or P0138.
7. 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].
P0139
1. Clear the DTCs (even if no DTCs are stored, perform the clear DTC operation) [A].
2. Turn the ignition switch off and wait for at least 30 seconds.
3. Start the engine and warm it up until the ECT reaches 75°C (167°F) or higher [B].
4. Drive the vehicle at 40 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].
5. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
6. Input DTCs: P0139.
7. 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 2 and then perform steps [C] through [D] again.
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.
1. Connect the Techstream to the DLC3.
2. Start the engine and turn the Techstream ON.
3. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
4. On the Techstream, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F sensor.
5. 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).
6. Monitor the voltage outputs of the A/F and HO2 sensors (AFS 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 Voltage:
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, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / A/F Control System / AFS B1 S1 and O2S B1 S2.
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. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.
- If the OX1B wire from the ECM connector is short-circuited to the +B wire, DTC P0136 will be set.
PROCEDURE
1. READ OUTPUT DTC (DTC P0136, P0137, P0138 OR P0139)
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to ON and turn the Techstream ON.
(c) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(d) Read DTCs.
Result:
D -- READ VALUE USING TECHSTREAM (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)
C -- PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE INJECTION VOLUME)
B -- CHECK FOR EXHAUST GAS LEAKAGE
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 ON and turn the Techstream ON.
(c) Enter the following menus: Powertrain / Engine and ECT / Data List / A/F Control System / O2S B1 S2.
(d) Allow the engine to idle.
(e) Read the Heated Oxygen (HO2) sensor output voltage while idling.
Result:
B -- PERFORM ACTIVE TEST USING TECHSTREAM (INJECTION VOLUME)
A -- Continue to next step.