SFI SYSTEM, Diagnostic DTC:P0136, P0137, P0138

DTC Code	DTC Name
P0136	Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
P0137	Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2)
P0138	Oxygen Sensor Circuit High Voltage (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 (TWC) is used. For the most efficient use of the Three-way Catalytic Converter (TWC), 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 (TWC), 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-Three-way Catalytic Converter (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 (TWC) 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 (TWC) 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 primary air-fuel ratio control.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	MIL	Memory
P0136	Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)	Abnormal voltage output: During active air-fuel ratio control, the following conditions (a) and (b) are met for a certain period of time (2 trip detection logic): (a) Heated oxygen sensor voltage does not increase to higher than 0.71 V. (b) Heated oxygen sensor voltage does not decrease to below 0.21 V.	Open or short in heated oxygen sensor circuit Heated oxygen sensor Heated oxygen sensor heater Air fuel ratio sensor Gas leak from exhaust system	Comes on	DTC stored
P0137	Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2)	Low voltage (open): During active air-fuel ratio control, the following conditions (a) and (b) are met for a certain period of time (2 trip detection logic): (a) Heated oxygen sensor voltage output is below 0.21 V. (b) Target air-fuel ratio is rich.	Open in heated oxygen sensor circuit Heated oxygen sensor Heated oxygen sensor heater Air fuel ratio sensor Gas leak from exhaust system	Comes on	DTC stored
P0138	Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2)	High voltage (short): During active air-fuel ratio control, the following conditions (a) and (b) are met for a certain period of time (2 trip detection logic): (a) Heated oxygen sensor voltage output is higher than 0.71 V. (b) Target air-fuel ratio is lean.	Short in heated oxygen sensor circuit Heated oxygen sensor Air fuel ratio sensor ECM	Comes on	DTC stored

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 (TWC) and heated oxygen 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.

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 0.71 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 (TWC) 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 decreases significantly, the Oxygen Storage Capacity (OSC) is indicated as having 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 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 0.71 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.

*: The Three-way Catalytic Converter (TWC) has the capability to store oxygen. The Oxygen Storage Capacity (OSC) and the emissions purification capacity of the Three-way Catalytic Converter (TWC) are mutually related. The ECM determines whether the catalyst has deteriorated based on the calculated Oxygen Storage Capacity (OSC) value Click here.

MONITOR STRATEGY

Required Sensors/Components (Main)

Heated oxygen sensor

Required Sensors/Components (Related)

Crankshaft position sensor

Engine coolant temperature sensor

Mass air flow meter sub-assembly

Throttle position sensor

Air fuel ratio sensor

Frequency of Operation

Once per driving cycle: Active air-fuel ratio control detection

Continuous: Other

TYPICAL ENABLING CONDITIONS

Heated Oxygen Sensor Output Voltage (Abnormal Voltage Output, High Voltage and Low Voltage)
Active air-fuel ratio control	Executing
Active air-fuel ratio control begins when all of following conditions met:	-
Battery voltage	11 V or higher
Engine coolant temperature	75°C (167°F) or higher
Idling	OFF
Engine speed	Less than 4000 rpm
Air fuel ratio sensor status	Activated
Fuel system status	Closed loop
Engine load	10 to 80%

TYPICAL MALFUNCTION THRESHOLDS

Heated Oxygen Sensor Output Voltage (Abnormal Voltage Output)
Either of following conditions met:	1 or 2
1. Both of following conditions met	(a) and (b)
(a) Commanded air-fuel ratio	14.3 or less
(b) Rear heated oxygen sensor voltage	0.21 to 0.71 V
2. Both of following conditions met	(c) and (d)
(c) Commanded air-fuel ratio	14.8 or more
(d) Rear heated oxygen sensor voltage	0.21 to 0.71 V

Heated Oxygen Sensor Output Voltage (Low)
Both of following conditions met	(a) and (b)
(a) Commanded air-fuel ratio	14.3 or less
(b) Rear heated oxygen sensor voltage	Below 0.21 V

Heated Oxygen Sensor Output Voltage (High)
Both of following conditions met	(a) and (b)
(a) Commanded air-fuel ratio	14.8 or more
(b) Rear heated oxygen sensor voltage	Higher than 0.71 V

CONFIRMATION DRIVING PATTERN

Connect the GTS to the DLC3.
Turn the ignition switch to ON and turn the GTS 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 GTS 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 5th gear or higher, drive the vehicle at 90 to 120 km/h (56 to 75 mph) for 10 minutes or more [C].

CAUTION:

When performing the confirmation driving pattern, obey all speed limits and traffic laws.
Enter the following menus: Powertrain / Engine and ECT / DTC [D].
Read the pending DTCs.
Tech Tips
- 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 or P0138.

Check the DTC judgment result.

GTS Display	Description
NORMAL	DTC judgment completed System normal
ABNORMAL	DTC judgment completed System abnormal
INCOMPLETE	DTC judgment not completed Perform driving pattern after confirming DTC enabling conditions
N/A	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit

Tech Tips

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, shift the transmission to 2nd gear, and then perform steps [C] and [D] again.

WIRING DIAGRAM

Refer to DTC P0037.

Click here

CAUTION / NOTICE / HINT

Tech Tips

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 GTS.

Connect the GTS to the DLC3.
Start the engine and turn the GTS on.
Warm up the engine and run 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 Active Test operation with the engine idling.
Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the GTS.

Tech Tips

Change the fuel injection volume within the range of -12.5% to +12.5%. The injection volume can be changed in fine gradations.
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.

GTS Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 (Air fuel ratio)	+12.5%	Rich	Below 3.1 V
AFS Voltage B1S1 (Air fuel ratio)	-12.5%	Lean	Higher than 3.4 V
O2S B1S2 (Heated oxygen)	+12.5%	Rich	Higher than 0.55 V
O2S B1S2 (Heated oxygen)	-12.5%	Lean	Below 0.4 V

Note

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.

Tech Tips

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 ratio 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 / All Data / AFS Voltage B1S1 and O2S B1S2.
Read freeze frame data using the GTS. 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 P0136 will be stored.
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.

PROCEDURE

READ OUTPUT DTC (DTC P0136, P0137 OR P0138)

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Powertrain > Engine > Trouble Codes

Read DTCs.

Result

Result	Proceed to
P0138 is output	A
P0137 is output	B
P0136 is output	C
P0136, P0137 or P0138 and other DTCs are output	D

CHECK FOR EXHAUST GAS LEAK Click here

PERFORM ACTIVE TEST USING GTS (CONTROL THE INJECTION VOLUME FOR A/F SENSOR) Click here

GO TO DTC CHART Click here

READ VALUE USING GTS (OUTPUT VOLTAGE OF HEATED OXYGEN SENSOR)

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / O2S B1S2.

Powertrain > Engine > Data List

Tester Display

O2S B1S2
Allow the engine to idle.

Tester Display
O2S B1S2

Read the heated oxygen sensor output voltage while idling.

Result

Heated Oxygen Sensor Output Voltage	Proceed to
1.0 V or higher	A
Below 1.0 V	B

PERFORM ACTIVE TEST USING GTS (CONTROL THE INJECTION VOLUME FOR A/F SENSOR) Click here

INSPECT HEATED OXYGEN SENSOR (CHECK FOR SHORT)

*a
Component without harness connected

(to Heated Oxygen Sensor for Bank 1)

Disconnect the heated oxygen sensor connector.

Measure the resistance according to the value(s) in the table below.

Standard Resistance

Tester Connection	Condition	Specified Condition
2 (+B) - 3 (OX1B)	Always	10 kΩ or higher
2 (+B) - 4 (E2)	Always	10 kΩ or higher

Result

Proceed to
OK
NG

REPLACE HEATED OXYGEN SENSOR Click here

CHECK HARNESS AND CONNECTOR (CHECK FOR SHORT)

Turn the ignition switch off and wait for 5 minutes.
Disconnect the ECM connector.

Measure the resistance according to the value(s) in the table below.

Standard Resistance

Tester Connection	Condition	Specified Condition
C147-7 (HT1B) - C147-27 (OX1B)	Always	10 kΩ or higher

Result

Proceed to
OK
NG

REPLACE ECM Click here

REPAIR OR REPLACE HARNESS OR CONNECTOR

PERFORM ACTIVE TEST USING GTS (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

Connect the GTS to the DLC3.
Start the engine.
Turn the GTS on.
Warm up the engine.

Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / All Data / AFS Voltage B1S1 and O2S B1S2.

Powertrain > Engine > Active Test

Active Test Display
Control the Injection Volume for A/F Sensor

Data List Display
AFS Voltage B1S1
O2S B1S2

Change the fuel injection volume using the GTS, and monitor the voltage output of the air fuel ratio sensor and heated oxygen sensor displayed on the GTS.

Tech Tips

The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.
The air fuel ratio sensor is displayed as AFS Voltage B1S1, and the heated oxygen sensor is displayed as O2S B1S2 on the GTS.
If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

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.

Result

GTS Display (Sensor)	Voltage Variation	Proceed to
AFS Voltage B1S1	Alternates between higher than and below 3.3 V	OK
	Remains higher than 3.3 V	NG
	Remains below 3.3 V	NG

Tech Tips

A normal heated oxygen sensor voltage (O2S B1S2) reacts in accordance with increases and decreases in fuel injection volumes. When the air fuel ratio sensor voltage remains either below or higher than 3.3 V despite the heated oxygen sensor indicating a normal reaction, the air fuel ratio sensor is malfunctioning.

GO TO STEP 7 Click here

INSPECT AIR FUEL RATIO SENSOR

Tech Tips

This air fuel ratio sensor test is to check the air fuel ratio sensor current during the fuel-cut. When the sensor is normal, the sensor current will be below 2.2 mA in this test.

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Clear DTCs.

Powertrain > Engine > Clear DTCs
Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.
Drive the vehicle at 60 km/h (37 mph) or more for 10 minutes or more.

CAUTION:

When performing the confirmation driving pattern, obey all speed limits and traffic laws.
Stop the vehicle.
Enter the following menus: Powertrain / Engine and ECT / Data List / AFS Current B1S1.

Powertrain > Engine > Data List

Tester Display

AFS Current B1S1

Tester Display
AFS Current B1S1

Drive the vehicle at 60 km/h (37 mph) or more for 10 minutes or more. Perform this 3 times.

CAUTION:

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

Driving Pattern
*a	60 km/h (37 mph)
*b	0 km/h (0 mph)
*c	10 minutes or more
*d	5 seconds or more

Read the value of the air fuel ratio sensor current while the fuel-cut operation is being performed.

Standard current
Below 2.2 mA

Tech Tips

To measure the air fuel ratio sensor current precisely, perform the fuel-cut operation as long as possible.
If it is difficult to measure the air fuel ratio sensor current, use the snapshot function of the GTS.

Result

Proceed to
OK
NG

GO TO STEP 13 Click here

REPLACE AIR FUEL RATIO SENSOR

Replace the air fuel ratio sensor.

Click here

Tech Tips

Perform "Inspection After Repair" after replacing the air fuel ratio sensor.

Click here

Result

Proceed to
NEXT

PERFORM CONFIRMATION DRIVING PATTERN

Perform Confirmation Driving Pattern (P0136, P0137 and P0138).

Result

Proceed to
NEXT

CHECK WHETHER DTC OUTPUT RECURS (DTC P0136, P0137 OR P0138 IS OUTPUT AGAIN)

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

Powertrain > Engine > Utility

Tester Display

All Readiness
Input DTCs: P0136, P0137 or P0138.

Check that the STATUS is NORMAL. If the STATUS is INCOMPLETE, perform the driving pattern again but increase the vehicle speed.

Result

Display (DTC Output)

Proceed to

NORMAL

(No DTC output)

ABNORMAL

(P0136, P0137 or P0138 output)

END

REPLACE HEATED OXYGEN SENSOR Click here

CHECK FOR EXHAUST GAS LEAK

Check for exhaust gas leakage.

OK
No gas leakage.

Tech Tips

Perform "Inspection After Repair" after repairing or replacing the exhaust system.

Click here

Result

Proceed to
OK
NG

REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT

INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE)

Inspect the heated oxygen sensor.

Click here

Result

Proceed to
OK
NG

REPLACE HEATED OXYGEN SENSOR Click here

CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - ECM)

Disconnect the heated oxygen sensor connector.
Disconnect the ECM connector.

Measure the resistance according to the value(s) in the table below.

Standard Resistance

Tester Connection	Condition	Specified Condition
C98-1 (HT1B) - C147-7 (HT1B)	Always	Below 1 Ω
C98-3 (OX1B) - C147-27 (OX1B)	Always	Below 1 Ω
C98-4 (E2) - C147-35 (EX1B)	Always	Below 1 Ω
C98-1 (HT1B) or C147-7 (HT1B) - Body ground	Always	10 kΩ or higher
C98-3 (OX1B) or C147-27 (OX1B) - Body ground	Always	10 kΩ or higher

Result

Proceed to
OK
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPLACE HEATED OXYGEN SENSOR

Replace the heated oxygen sensor.

Click here

Result

Proceed to
NEXT

PERFORM CONFIRMATION DRIVING PATTERN

Perform Confirmation Driving Pattern (P0136, P0137 and P0138).

Result

Proceed to
NEXT

CHECK WHETHER DTC OUTPUT RECURS (DTC P0136, P0137 OR P0138 IS OUTPUT AGAIN)

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

Powertrain > Engine > Utility

Tester Display

All Readiness
Input DTCs: P0136, P0137 or P0138.

Check that the STATUS is NORMAL. If the STATUS is INCOMPLETE, perform the driving pattern again but increase the vehicle speed.

Result

Display (DTC Output)

Proceed to

NORMAL

(No DTC output)

ABNORMAL

(P0136, P0137 or P0138 output)

END

REPLACE AIR FUEL RATIO SENSOR Click here

PERFORM ACTIVE TEST USING GTS (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

Connect the GTS to the DLC3.
Start the engine.
Turn the GTS on.
Warm up the engine.
Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / All Data / O2S B1S2.

Powertrain > Engine > Active Test

Active Test Display

Control the Injection Volume for A/F Sensor

Data List Display

O2S B1S2

Change the fuel injection volume using the GTS and monitor the voltage output of the heated oxygen sensor displayed on the GTS.

Tech Tips

The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.
The heated oxygen sensor has a maximum output delay of approximately 20 seconds.

Standard voltage
Fluctuates between 0.4 V or less and 0.5 V or higher.

Result

Proceed to
OK
NG

GO TO STEP 10 Click here

PERFORM ACTIVE TEST USING GTS (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

Connect the GTS to the DLC3.
Turn the GTS on.
Start the engine.
Warm up the engine.

Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / All Data / AFS Voltage B1S1 and O2S B1S2.

Powertrain > Engine > Active Test

Active Test Display
Control the Injection Volume for A/F Sensor

Data List Display
AFS Voltage B1S1
O2S B1S2

Change the fuel injection volume using the GTS and monitor the voltage output of the air fuel ratio and heated oxygen sensor displayed on the GTS.

Tech Tips

The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.
The air fuel ratio sensor is displayed as AFS Voltage B1S1, and the heated oxygen sensor is displayed as O2S B1S2 on the GTS.
If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.
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.

Result

GTS Display (Sensor)	Voltage Variation	Proceed to
AFS Voltage B1S1	Alternates between higher than and below 3.3 V	OK
	Remains higher than 3.3 V	NG
	Remains below 3.3 V	NG

Tech Tips

CHECK EXTREMELY RICH OR LEAN ACTUAL AIR FUEL RATIO AND REPAIR CAUSE (FUEL INJECTOR ASSEMBLY, FUEL PRESSURE, GAS LEAK FROM SYSTEM)

GO TO STEP 7 Click here