P0138

DTC P0136 Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
DTC P0138 Heated Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2)
DTC P0139 Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 2)

DESCRIPTION

DTC Detecting Condition:

The rear Heated Oxygen (HO2) sensor (bank 1 sensor 2) is located behind the Three-Way Catalytic Converter (TWC), and detects the oxygen concentration in the exhaust gas. For optimum TWC operation, the air fuel mixture must be maintained as close as possible to the stoichiometric ratio. The HO2 sensor output voltage changes dramatically in the vicinity of the stoichiometric ratio. By making adjustments in accordance with these signal voltage changes, the ECM adjusts the fuel injection time so that the air-fuel ratio remains as close as possible to stoichiometric levels.

The rear HO2 sensor generates a voltage that ranges from 0.1 V to 0.9 V according to the oxygen concentration in the exhaust gas. When the oxygen concentration in the exhaust gas increases, the HO2 sensor voltage drops below 0.45 V. The ECM interprets this as the air-fuel ratio being lean. Alternatively, the sensor voltage rises to more than 0.45 V when there is no oxygen in the exhaust gas. The ECM interprets this as the air-fuel ratio being rich.

MONITOR DESCRIPTION

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds (Part 1):

Typical Malfunction Thresholds (Part 2):

Component Operating Rage:

The ECM monitors the HO2 sensor (bank 1 sensor 2) to check for the following malfunctions. If any one of the malfunctions is detected, the ECM illuminates the MIL and sets a DTC:
- The HO2 sensor output voltage remains above 0.5 V (rich) or below 0.4 V (lean) while the vehicle is accelerated and decelerated for 4 to 8 minutes.
- The HO2 sensor output voltage remains extremely low, below 0.05 V for a long time period of time while the vehicle is driven.
- The HO2 sensor output voltage remains extremely low, below 0.2 V (extremely lean condition) soon after fuel cut is performed while the vehicle is decelerated. The ECM interprets this as the sensor response having deteriorated.
- The HO2 sensor output voltage exceeds more than 1.2 V for 10 seconds.

MONITOR RESULT

Refer to detailed information. Mode 6 Data

CONFIRMATION DRIVING PATTERN

This confirmation driving pattern is used in the "PERFORM CONFIRMATION DRIVING PATTERN" procedure of the following diagnostic troubleshooting procedure.

CAUTION: Strictly observe posted speed limits, traffic laws, and road conditions when performing the driving pattern below.

1. Preconditions

The Heated Oxygen (HO2) sensor monitor will not run unless:
- 2 minutes or more have elapsed since the engine was started.
- The Engine Coolant Temperature (ETC) is 75 degrees C (167 degrees F) or more.
- Cumulative driving time at a vehicle speed of 48 km/h (30 mph) or more exceeds 6 minutes.
- Air-fuel ratio feedback control is performed.
- Fuel cut control is performed for 8 seconds or more (for the rear HO2 sensor).

2. Driving Patterns

a. Connect the intelligent tester to the DLC3.
b. Turn the ignition switch ON and turn the tester ON.
c. Clear DTCs.
d. Start the engine and warm it up until the ETC reaches 75 degrees C (167 degrees F) or higher.
e. Drive the vehicle at 48 km/h (30 mph) or more for at least 40 seconds. f. Allow the engine to idle for 20 seconds or more.
9. Repeat steps e. and f. described above at least 8 times in 1 driving cycle.
h. Change the transmission to 2nd gear.
i. Accelerate the vehicle to 48 km/h (30 mph) or more by depressing the accelerator pedal for at least 10 seconds.




j. Soon after performing step (i) above, release the accelerator pedal for at least 10 seconds without depressing the brake pedal in order to execute fuel cut control.
k. Allow the vehicle to decelerate to less than 10 km/h (6 mph).
l. Repeat steps from (i) through (k) described above at least twice in 1 driving cycle.

HINT: Malfunctioning areas can be identified by performing the A/F CONTROL function provided in the ACTIVE TEST. The A/F CONTROL function can help to determine whether the Heated Oxygen (HO2) sensors and other potential trouble areas are malfunctioning.

The following instructions describe how to conduct the A/F CONTROL operation using the intelligent tester.

1. Connect the intelligent tester to the DLC3.
2. Start the engine and turn the tester ON.
3. Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
4. Enter the following menus: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL.
5. Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
6. Monitor the voltage output of the HO2 sensors (O2S B1S1 and O2S B1S2) displayed on the tester.






HINT:
- The A/F CONTROL 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.






NOTE: The front HO2 sensor has an output delay of a few seconds and the rear HO2 sensor has a maximum output delay of approximately 20 seconds.

- Following the A/F CONTROL procedure enables technicians to check and graph the voltage outputs of both the front and rear HO2 sensors.
- To display the graph, enter the following menus on the tester: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST/ A/F CONTROL / USER DATA / O2S B1S1 and O2S B1S2; then press the YES button and ENTER button followed by the F4 button.

Wiring Diagram:

Step 1-2:

Step 3-5:

Step 5(Continued)-7:

Step 7(Continued):

INSPECTION PROCEDURE

NOTE: If the vehicle is short of fuel, the air-fuel ratio becomes lean, HO2 sensor DTCs are recorded, and the ECM illuminates the MIL.

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 intelligent tester. 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.
- A high HO2 sensor (sensor 1) voltage (0.55 V or more) could be caused by a rich air fuel mixture. Check for conditions that would cause the engine to run rich.
- A low HO2 sensor (sensor 1) voltage (0.4 V or less) could be caused by a lean air fuel mixture. Check for conditions that would cause the engine to run lean.