Part 1
2TR-FE ENGINE CONTROL: SFI SYSTEM: P0136-P0139: Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
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 three-way catalytic converter is used. For the most efficient use of the three-way catalytic converter, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio. For the purpose of helping the ECM to deliver accurate air-fuel ratio control, a heated oxygen sensor is used.
The heated oxygen sensor is located behind the three-way catalytic converter, and detects the oxygen concentration in the exhaust gas. Since the sensor is integrated with a 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 heated oxygen sensor informs the ECM that the post-TWC air-fuel ratio is lean (low voltage, i.e. below 0.45 V).
Conversely, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas becomes lean. The heated oxygen sensor informs the ECM that the post-three-way catalytic converter air-fuel ratio is rich (high voltage, i.e. higher than 0.45 V). The heated oxygen 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 heated oxygen sensor to determine whether the air-fuel ratio after the three-way catalytic converter is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the heated oxygen 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
Active Air-Fuel Ratio Control
The ECM usually performs air-fuel ratio feedback control so that the air fuel ratio sensor output indicates a near stoichiometric air-fuel ratio. 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 and heated oxygen sensor (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 stored: DTC P0136 (abnormal voltage output), P0137 (open circuit), P0138 (short circuit) or P0139.
Abnormal Voltage Output of Heated Oxygen 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 heated oxygen sensor voltage does not decrease to below 0.21 V and does not increase to higher than 0.59 V during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormal and stores DTC P0136.
Open or Short in Heated Oxygen 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 by forcibly regulating the air-fuel ratio to become rich or lean. If the heated oxygen sensor has an open or short circuit, or the voltage output of the sensor decreases significantly, the OSC is indicated as having an abnormally high value. Even if the ECM attempts to continue regulating the air-fuel ratio to become rich or lean, the heated oxygen sensor output does not change.
While performing active air-fuel ratio control, when the target air-fuel ratio is rich and the heated oxygen sensor voltage output is 0.21 V or less (lean), the ECM interprets this as an abnormally low sensor output voltage and stores DTC P0137. When the target air-fuel ratio is lean and the voltage output is 0.59 V or higher (rich) during active air-fuel ratio control, the ECM determines that the sensor voltage output is abnormally high and stores DTC P0138.
HINT
DTC P0138 is also stored if the heated oxygen sensor voltage output is higher than 1.2 V for 10 seconds or more.
*: The three-way catalytic converter has the capability to store oxygen. The OSC and the emissions purification capacity of the three-way catalytic converter are mutually related. The ECM determines whether the catalyst has deteriorated based on the calculated OSC value P0420.
High or Low Impedance of Heated Oxygen 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 variations in the heated oxygen 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 deterioration of the heated oxygen sensor. The ECM stores this DTC by calculating the impedance of the sensor when the typical enabling conditions are satisfied (2 driving cycles).
- DTC P0137 indicates an open or short circuit in the heated oxygen sensor (2 driving cycles). The ECM stores this DTC when the impedance of the sensor exceeds the threshold of 15 kOhms.
Heated Oxygen Sensor Output Voltage during Fuel Cut (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, the ECM determines that the sensor response has deteriorated, illuminates the MIL and stores a DTC.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
TYPICAL MALFUNCTION THRESHOLDS
COMPONENT OPERATING RANGE
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 operation).
* Turn the ignition switch off and wait for at least 30 seconds.
* 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 60 to 120 km/h (40 to 75 mph) for 10 minutes or more [C].
* Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [D].
* Read the pending DTCs.
HINT
- If a pending DTC is output, the system is malfunctioning.
- If a pending DTC is not output, perform the following procedure.
* Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
* Input the DTC: P0136, P0137 and P0138.
* Check the DTC judgment result.
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 no pending DTC is output, perform a universal trip and check for permanent DTCs DTC Check / Clear.
HINT
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.
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 operation).
* Turn the ignition switch off and wait for at least 30 seconds.
* 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 60 km/h (40 mph), and then decelerate the vehicle by releasing the accelerator pedal for 10 seconds or more to perform the fuel-cut [C].
* Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [D].
* Read the DTCs.
HINT
- If a pending DTC or current DTC is output, the system is malfunctioning.
- If a pending DTC or current DTC is not output, perform the following procedure.
* Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
* Input the DTC: P0139.
* Check the DTC judgment result.
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.
* If no pending DTC is output, perform a universal trip and check for permanent DTCs DTC Check / Clear.
HINT
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.
MONITOR RESULT
Refer to Checking Monitor Status Mode 6 Data.
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT
Techstream only:
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 sensor, heated oxygen 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 2500 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 idling (press the RIGHT or LEFT button to change the fuel injection volume).
* Monitor the voltage outputs of the air fuel and heated oxygen sensors (AFS Voltage B1S1 and O2S 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%.
- The sensors react in accordance with increases and decreases in the fuel injection volume.
Standard:
NOTICE:
The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen 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 air fuel and heated oxygen sensors.
* To display the graph, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F sensor / AFS Voltage B1S1 and O2S B1S2. Then press the graph button on the Data List display.
HINT
- 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 P0138 will be stored.