Part 1

2ZR-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
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), hydrocarbons (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 level. 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 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 heated oxygen sensor informs the ECM that the post-three-way catalytic converter 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 level, 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.









for Mexico Models





MONITOR DESCRIPTION

1. 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 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 and heated oxygen sensor malfunctions (refer to the diagram below).

Active air fuel ratio control is performed for approximately 30 seconds or more 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 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 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 DTCs P0136.





3. Open or Short in Heated Oxygen Sensor Circuit (DTC P0137)

During active air fuel ratio control, the ECM 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 the voltage output of the sensor noticeably decreases, the oxygen storage capacity indicates an extraordinarily 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 below 0.21 V (lean), the ECM interprets this as an abnormally low sensor output voltage and stores DTC P0137.

*: 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 ECM 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 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 heated oxygen sensor. The ECM stores the DTCs 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 the DTCs when the impedance of the sensor exceeds the threshold of 15 kOhms.

5. Extremely High Output Voltage of Heated Oxygen Sensor (DTC P0138)

The ECM continuously monitors the heated oxygen sensor output voltage while the engine is running.

DTC P0138 is stored if the heated oxygen sensor voltage output is 1.2 V or higher for 10 seconds or more.

6. 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 the voltage does not drop from 0.35 to 0.2 V for 1 second or more, the ECM determines that the sensor response has deteriorated, illuminates the MIL and stores a DTC.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS

All





P0136 and P0137: Heated Oxygen Sensor (Sensor 2) Voltage Check (Voltage Malfunction and Low Voltage)





P0136: Heated Oxygen Sensor Circuit (Sensor 2) Continuity Check (Circuit Short)





P0137: Heated Oxygen Sensor Circuit (Sensor 2) Continuity Check (Circuit Open)





P0138: Heated Oxygen Sensor Circuit (Sensor 2) Continuity Check (Out of Range)





P0139: Heated Oxygen Sensor (Sensor 2) Response Rate During Fuel Cut





TYPICAL MALFUNCTION THRESHOLDS

P0136: Heated Oxygen Sensor (Sensor 2) Voltage Check (Voltage Malfunction)





P0137: Heated Oxygen Sensor (Sensor 2) Voltage Check (Low Voltage)





P0136: Heated Oxygen Sensor (Sensor 2) Circuit Continuity Check (Circuit Short)





P0137: Heated Oxygen Sensor (Sensor 2) Circuit Continuity Check (Circuit Open)





P0138: Heated Oxygen Sensor (Sensor 2) Circuit Continuity Check (Out of Range)





P0139: Heated Oxygen Sensor (Sensor 2) Response Rate During Fuel Cut





MONITOR RESULT

Refer to detailed information in Checking Monitor Status Mode 6 Data.

P0137: O2 Sensor / MAX VOL B1S2





P0139: O2 Sensor / RL F/C B1S2





P0139: O2 Sensor / F/C TIME B1S2





P0136: O2 Sensor / MAX OSC B1S2





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.