Part 1

2ZR-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

HINT
Sensor 2 refers to the sensor mounted behind the Three-Way Catalytic Converter (TWC) and located far from the engine assembly.

In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxides (NOx) components in the exhaust gas, a TWC (Three-Way Catalytic Converter) 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, a DTC is stored.

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 stores 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 less than 0.21 V (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 more (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 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.

HINT
- The impedance cannot be measured using an ohmmeter.
- DTCs P0136 indicate the deterioration of the HO2 sensor. The ECM stores 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 stores 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 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

All:

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 Voltage During Fuel cut:

TYPICAL MALFUNCTION THRESHOLDS

Heated Oxygen Sensor Output Voltage (Output voltage):

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 Voltage During Fuel-cut:

COMPONENT OPERATING RANGE

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 (HO2) 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 ignition switch to ON and turn the Techstream on.

3. Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).

4. Turn the ignition switch off and wait for at least 30 seconds.

5. Turn the ignition switch to ON and turn the Techstream on [A].

6. Start the engine and warm it up until the ECT reaches 75°C (167°F) or higher [B].

7. Drive the vehicle at 60 to 120 km/h (37 to 75 mph) for 10 minutes or more [C].

CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.

8. Enter the following menus: Powertrain / Engine and ECT / Trouble Code [D].

9. Read pending DTCs.

HINT
- If a pending DTC is output, the system is malfunctioning.
- If a pending DTC or current DTC is not output, perform the following procedure.

10. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

11. Input the DTC: P0136, P0137 or P0138.

12. 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 steps [C] through [D].

13. If the test result is INCOMPLETE or N/A and 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 ignition switch to ON and turn the Techstream on.

3. Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).

4. Turn the ignition switch off and wait for at least 30 seconds.

5. Turn the ignition switch to ON and turn the Techstream on [A].

6. Start the engine and warm it up until the ECT reaches 75°C (167°F) or higher [B].

7. Drive the vehicle at 60 km/h (37 mph), and then decelerate the vehicle by releasing the accelerator pedal for 8 seconds or more to perform the fuel-cut [C].

CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.

8. Enter the following menus: Powertrain / Engine and ECT / Trouble Code [D].

9. Read pending DTCs.

HINT
- If a pending DTC is output, the system is malfunctioning.
- If a pending DTC or current DTC is not output, perform the following procedure.

10. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

11. Input the DTC: P0139.

12. Check the DTC judgment result.