Part 1
2AZ-FXE ENGINE CONTROL: SFI SYSTEM: P0136-P0139: Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
P0139 - Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 2)
DESCRIPTION
HINT
Bank 1 sensor 2 refers to the sensor mounted behind the three way catalytic converter and located far from the engine assembly.
A three way catalytic converter is used in order to convert the carbon monoxide, hydrocarbons, and nitrogen oxide, into less harmful substances. To allow the three way catalytic converter 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 hybrid vehicle control ECU 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 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 great. The heated oxygen sensor informs the hybrid vehicle control ECU that the post-three way catalytic converter 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 small. The heated oxygen sensor informs the hybrid vehicle control ECU that the post-three way catalytic converter air fuel ratio is rich (high voltage, i.e. more 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 hybrid vehicle control ECU 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 hybrid vehicle control ECU is unable to compensate for deviations in the primary air fuel ratio control.
MONITOR DESCRIPTION
1. Active Air Fuel Ratio Control
The hybrid vehicle control ECU usually performs air fuel ratio feedback control so that the air fuel ratio 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 hybrid vehicle control ECU performs active air fuel ratio control to detect any deterioration in the three-way catalytic converter and heated oxygen sensor malfunctions (refer to the diagram below).
Active air fuel ratio control is performed for approximately 15 to 25 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 hybrid vehicle control ECU. If the hybrid vehicle control ECU detects a malfunction, a DTC is set.
2. Abnormal Voltage Output of Heated Oxygen Sensor (DTC P0136)
While the hybrid vehicle control ECU 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 less than 0.21 V, or does not increase to mote than 0.59 V during active air fuel ratio control, the hybrid vehicle control ECU determines that the sensor voltage output is abnormal and sets DTC P0136.
3. Open or Short in Heated Oxygen Sensor Circuit (DTCs P0137 or P0138)
During active air fuel ratio control, the hybrid vehicle control ECU calculates the oxygen storage capacity* 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, or the voltage output of the sensor noticeably decreases, the oxygen storage capacity indicates an extraordinarily high value. Even if the hybrid vehicle control ECU 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 less than 0.21 V (lean), the hybrid vehicle control ECU 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 hybrid vehicle control ECU determines that the sensor voltage output is abnormally high, and sets DTC P0138.
HINT
DTC P0138 is also set if the heated oxygen sensor voltage output is more than 1.2 V for 10 seconds or more.
*: The three-way catalytic converter has the capability to store oxygen. The oxygen storage capacity and the emission purification capacity of the three-way catalytic converter are mutually related. The hybrid vehicle control ECU determines whether the catalyst has deteriorated, based on the calculated oxygen storage capacity value P0420.
4. High or Low Impedance of Heated Oxygen 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 heated oxygen sensor signal while the engine is running, the impedance* of the sensor is measured by the hybrid vehicle control ECU. The hybrid vehicle control ECU 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 heated oxygen sensor. The hybrid vehicle control ECU stores the 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 hybrid vehicle control ECU stores the DTC when the impedance of the sensor exceeds the threshold of 15 kOhms.
5. Abnormal Voltage Output of Heated Oxygen 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 6 seconds or more, or voltage does not drop from 0.35 V to 0.2 V for 1 second or more, the hybrid vehicle control ECU determines that the sensor response has deteriorated, illuminates the MIL and sets a DTC.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
All
P0136, P0137, P0138: Heated Oxygen Sensor Output Voltage Check (Voltage Malfunction, High Voltage and Low Voltage)
P0136: Heated Oxygen Sensor Circuit Continuity Check (Circuit Short)
P0137: Heated Oxygen Sensor Circuit Continuity Check (Circuit Open)
P0138: Heated Oxygen Sensor Circuit Continuity Check (Out of Range)
P0139: Heated Oxygen Sensor Response Rate During Fuel Cut
TYPICAL MALFUNCTION THRESHOLDS
P0136: Heated Oxygen Sensor Voltage Check (Voltage Malfunction)
P0137: Heated Oxygen Sensor Voltage Check (Low Voltage)
P0138: Heated Oxygen Sensor Voltage Check (High Voltage)
P0136: Heated Oxygen Sensor Circuit Continuity Check (Circuit Short)
P0137: Heated Oxygen Sensor Circuit Continuity Check (Circuit Open)
P0138: Heated Oxygen Sensor Circuit Continuity Check (Out of Range)
P0139: Heated Oxygen Sensor Response Rate During Fuel Cut
MONITOR RESULT
Refer to Checking Monitor Status Mode 6 Data.
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 sensor monitor (The catalyst monitor is performed simultaneously). This is very useful for verifying the completion of a repair.
P0136, P0137 and P0138
1. Connect the Techstream to the DLC3.
2. Turn the power switch on (IG) and turn the Techstream on.
3. Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure) Reading and Clearing Diagnostic Trouble Codes.
4. Turn the power switch off and wait for 30 seconds.
5. Turn the power switch on (IG) and turn the Techstream on [A].
6. Put the engine in inspection mode (maintenance mode) Component Tests and General Diagnostics.
7. Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher [B].
8. Drive the vehicle at 75 to 120 km/h (47 to 75 mph) for 10 minutes or more [C].
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [D].
10. 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.
11. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
12. Input the DTC: P0136, P0137 or P0138.
13. Check the DTC judgment result.
HINT
- If the judgment result shows NORMAL, the system is normal.
- If the judgment result shows ABNORMAL, the system has a malfunction.
- If the judgment result shows INCOMPLETE or N/A, perform step [C] and [D] again.
14. If no pending DTC is output, perform a universal trip and check for permanent DTCs Reading and Clearing Diagnostic Trouble Codes.
HINT
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.
P0139
1. Connect the Techstream to the DLC3.
2. Turn the power switch on (IG) and turn the Techstream on.
3. Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure) Reading and Clearing Diagnostic Trouble Codes.
4. Turn the power switch off and wait for 30 seconds.
5. Turn the power switch on (IG) and turn the Techstream on [A].
6. Put the engine in inspection mode (maintenance mode) Component Tests and General Diagnostics.
7. Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher [B].
8. Drive the vehicle at 75 km/h (47 mph), and then decelerate the vehicle by releasing the accelerator pedal for 5 seconds or more to perform the fuel-cut [C].
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [D].
10. 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.
11. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
12. Input the DTC: P0139.
13. Check the DTC judgment result.
HINT
- If the judgment result shows NORMAL, the system is normal.
- If the judgment result shows ABNORMAL, the system has a malfunction.
- If the judgment result shows INCOMPLETE or N/A, move the shift lever to B and then perform step [C] and [D] again.
14. If no pending DTC is output, perform a universal trip and check for permanent DTCs Reading and Clearing Diagnostic Trouble Codes.
HINT
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.
WIRING DIAGRAM
Refer to DTC P0037 P0037.