SFI SYSTEM (w/ Secondary Air Injection System), Diagnostic DTC:P0137

DTC Code DTC Name
P0137 Oxygen Sensor Circuit Low 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.

A01J32GE02
DTC No. DTC Detection Condition Trouble Area
P0137

  • 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

  • Integration relay

  • Gas leak from exhaust system

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.

Open in Heated Oxygen Sensor Circuit (DTC P0137)

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.

*: 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.

A01J562E12

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 and air fuel ratio sensor
Frequency of Operation Once per driving cycle

TYPICAL ENABLING CONDITIONS

Heated Oxygen Sensor Output Voltage (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 (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

CONFIRMATION DRIVING PATTERN

A01J73LE86

  1. Connect the intelligent tester to the DLC3.

  2. Turn the ignition switch to ON and turn the intelligent tester on.

  3. Clear the 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 intelligent tester on [A].

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

  7. 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.

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

  9. 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.

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

  11. Input the DTC: P0137.

  12. Check the DTC judgment result.

    Intelligent tester 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

A01J2ZOE13

INSPECTION PROCEDURE

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 intelligent tester.


  1. Connect the intelligent tester to the DLC3.

  2. Start the engine and turn the intelligent tester on.

  3. Warm up the engine and run the engine at an engine speed of 2500 rpm for approximately 90 seconds.

  4. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

  5. Perform the Active Test operation with the engine idling.

  6. Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the intelligent tester.

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.

Intelligent tester Display (Sensor) Injection Volume Status Voltage

AFS Voltage B1S1

(A/F)

 +12.5% Rich Below 3.1 V

AFS Voltage B1S1

(A/F)

 -12.5% Lean Higher than 3.4 V

O2S B1S2

(HO2)

 +12.5% Rich Higher than 0.55 V

O2S B1S2

(HO2)

 -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.

Case Air Fuel Ratio Sensor (Sensor 1) Output Voltage Heated Oxygen Sensor (Sensor 2) Output Voltage Main Suspected Trouble Area
1 A01J4ZQE08 A01J4QME08 A01J4ZQE08 A01J3I9E06 -
2 A01J4ZQE08 A01J6UEE01 A01J4ZQE08 A01J3I9E06

  • Air fuel ratio sensor

  • Air fuel ratio sensor heater

  • Air fuel ratio sensor circuit
3 A01J4ZQE08 A01J4QME08 A01J4ZQE08 A01J6UEE01

  • Heated oxygen sensor

  • Heated oxygen sensor heater

  • Heated oxygen sensor circuit
4 A01J4ZQE08 A01J6UEE01 A01J4ZQE08 A01J6UEE01

  • Fuel injector assembly

  • Fuel pressure

  • Gas leak from exhaust system (air-fuel ratio extremely rich or lean)

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 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.

  • Sensor 1 refers to the sensor closest to the engine assembly.

  • Sensor 2 refers to the sensor farthest away from the engine assembly.

PROCEDURE


  1. READ OUTPUT DTC


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the intelligent tester on.

    4. Enter the following menus: Powertrain / Engine and ECT / DTC.

    5. Read DTCs.

      Result
      Result Proceed to
      P0137 is output A
      P0137 and other DTCs are output B

    B

    GO TO DTC CHART Click here

    A

  2. CHECK FOR EXHAUST GAS LEAK


    1. Check for exhaust gas leakage.

      OK
      No gas leakage.

    NG

    REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT

    OK

  3. INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE)


    1. Inspect the heated oxygen sensor Click here.


    NG

    REPLACE HEATED OXYGEN SENSOR Click here

    OK

  4. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - ECM)


    1. Disconnect the heated oxygen sensor connector.

    2. Disconnect the ECM connector.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      H12-1 (HT1B) - E11-2 (HT1B) Always Below 1 Ω
      H12-3 (OX1B) - E11-25 (OX1B) Always Below 1 Ω
      H12-4 (E2) - E11-28 (E2) Always Below 1 Ω
      H12-1 (HT1B) or E11-2 (HT1B) - Body ground Always 10 kΩ or higher
      H12-3 (OX1B) or E11-25 (OX1B) - Body ground Always 10 kΩ or higher

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  5. REPLACE HEATED OXYGEN SENSOR


    1. Replace the heated oxygen sensor Click here.


    NEXT

  6. PERFORM CONFIRMATION DRIVING PATTERN


    1. Perform Confirmation Driving Pattern.


    NEXT

  7. CHECK WHETHER DTC OUTPUT RECURS (DTC P0137 IS OUTPUT AGAIN)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the intelligent tester on.

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

    4. Input DTCs: P0137.

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

      Result
      Display (DTC Output) Proceed to

      ABNORMAL

      (P0137 output)

      		 A

      NORMAL

      (No DTC output)

      		 B

    B

    END

    A

    REPLACE AIR FUEL RATIO SENSOR Click here