SFI SYSTEM, Diagnostic DTC:P0031, P0032, P101D

DTC Code DTC Name
P0031 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
P0032 Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)
P101D A/F Sensor Heater Circuit Performance Bank 1 Sensor 1 Stuck ON

DESCRIPTION

The air fuel ratio sensor generates a voltage* that corresponds to the actual air-fuel ratio. This sensor voltage is used to provide the ECM with feedback so that it can control the air-fuel ratio. The ECM determines the deviation from the stoichiometric air-fuel ratio and regulates the fuel injection time. If the air fuel ratio sensor malfunctions, the ECM is unable to control the air-fuel ratio accurately.

The air fuel ratio sensor is of the planar type and is integrated with a heater, which heats the solid electrolyte (zirconia element). This heater is controlled by the ECM. When the intake air volume is low (the exhaust gas temperature is low), a current flows through the heater to heat the sensor in order to facilitate accurate air-fuel ratio detection. In addition, the sensor and heater portions are the narrow type. The heat generated by the heater is conducted to the solid electrolyte through the alumina, thereby accelerating the sensor activation.

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 level.

*: The value changes inside the ECM. Since the air fuel ratio sensor is a current output element, the current is converted into a voltage inside the ECM. Any measurements taken at the air fuel ratio sensor or ECM connectors will show a constant voltage.

A005KQNE03

Tech Tips


  • Although the DTC titles say oxygen sensor, these DTCs relate to the air fuel ratio sensor.

  • Sensor 1 refers to the sensor mounted in front of the Three-way Catalytic Converter (TWC) and located near the engine assembly.

  • When one of these DTCs is stored, the ECM enters fail-safe mode. The ECM turns off the air fuel ratio sensor heater in fail-safe mode. The ECM continues operating in fail-safe mode until the ignition switch is turned off.

  • The ECM provides a pulse-width modulated control circuit to adjust the current through the heater. The air fuel ratio sensor heater circuit uses a relay on the +B side of the circuit.

    A005HHNE02
DTC No. DTC Detection Condition Trouble Area
P0031

Air fuel ratio sensor heater current less than 0.8 A

(1 trip detection logic)

  • Open in air fuel ratio sensor heater circuit

  • Air fuel ratio sensor heater (bank 1 sensor 1)

  • ECM power source circuit

  • ECM
P0032

Air fuel ratio sensor heater current fail

(1 trip detection logic)

  • Short in air fuel ratio sensor heater circuit

  • Air fuel ratio sensor heater (bank 1 sensor 1)

  • ECM power source circuit

  • ECM
P101D The heater current is at the specified value or higher while the heater is not operating (1 trip detection logic) ECM

MONITOR DESCRIPTION

The ECM uses information from the air fuel ratio sensor to regulate the air-fuel ratio and keep it close to the stoichiometric level. This maximizes the ability of the Three-way Catalytic Converter (TWC) to purify the exhaust gases.

The air fuel ratio sensor detects oxygen levels in the exhaust gas and transmits the information to the ECM. The inner surface of the sensor element is exposed to the outside air. The outer surface of the sensor element is exposed to the exhaust gas. The sensor element is made of platinum coated zirconia and includes an integrated heating element.

The zirconia element generates a small voltage when there is a large difference in the oxygen concentrations between the exhaust gas and outside air. The platinum coating amplifies this voltage generation.

The air fuel ratio sensor is more efficient when heated. When the exhaust gas temperature is low, the sensor cannot generate useful voltage signals without supplementary heating. The ECM regulates the supplementary heating using a duty cycle approach to adjust the average current in the sensor heater element. If the heater current is outside the normal range, the signal transmitted by the air fuel ratio sensor becomes inaccurate. As a result, the ECM is unable to regulate the air-fuel ratio properly.

When the current in the air fuel ratio sensor heater is outside the normal operating range, the ECM interprets this as a malfunction in the sensor heater and stores a DTC.

CONFIRMATION DRIVING PATTERN

A005LOBE21

  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 idle it for 5 minutes or more [B].

  7. With the vehicle stationary, depress the accelerator pedal and maintain an engine speed of 3000 rpm for 1 minute [C].

  8. Idle the engine for 5 minutes or more [D].

  9. Enter the following menus: Powertrain / Engine and ECT / DTC [E].

  10. 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.

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

  12. Input the DTC: P0031, P0032 or P101D.

  13. 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
    UNKNOWN

    • 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 UNKNOWN, perform steps [B] through [E] again.

WIRING DIAGRAM

A005LZTE03
A005LZTE04

CAUTION / NOTICE / HINT

Note

Inspect the fuses for circuits related to this system before performing the following inspection procedure.

Tech Tips


  • 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.

  • Refer to "Data List / Active Test" [A/F Heater Duty #1] Click here.

  • Change the fuel injection volume using the Control the Injection Volume function provided in the Active Test and monitor the air fuel ratio sensor output voltage Click here. If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

PROCEDURE


  1. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. Inspect the air fuel ratio sensor Click here.

      Tech Tips

      Perform "Inspection After Repairs" after replacing the air fuel ratio sensor Click here.


    NG

    REPLACE AIR FUEL RATIO SENSOR Click here

    OK

  2. CHECK TERMINAL VOLTAGE (POWER SOURCE)


    1. A005M3YE02
      Text in Illustration
      *a

      Front view of wire harness connector

      (to Air Fuel Ratio Sensor)

      Disconnect the air fuel ratio sensor connector.

    2. Turn the ignition switch to ON.

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

      Standard Voltage
      Tester Connection Switch Condition Specified Condition
      B39-2 (+B) - Body ground Ignition switch ON 11 to 14 V

    4. Reconnect the air fuel ratio sensor connector.


    NG

    INSPECT NO. 1 INTEGRATION RELAY (EFI MAIN) Click here

    OK

  3. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM)


    1. Disconnect the air fuel ratio sensor connector.

    2. Disconnect the ECM connector.

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

      Standard Resistance (Check for Open)
      for RHD
      Tester Connection Condition Specified Condition
      B39-1 (HA1A) - B23-23 (HA1A) Always Below 1 Ω
      for LHD
      Tester Connection Condition Specified Condition
      B39-1 (HA1A) - B22-23 (HA1A) Always Below 1 Ω
      Standard Resistance (Check for Short)
      for RHD
      Tester Connection Condition Specified Condition
      B39-1 (HA1A) or B23-23 (HA1A) - Body ground Always 10 kΩ or higher
      for LHD
      Tester Connection Condition Specified Condition
      B39-1 (HA1A) or B22-23 (HA1A) - Body ground Always 10 kΩ or higher

    4. Reconnect the air fuel ratio sensor connector.

    5. Reconnect the ECM connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  4. CHECK WHETHER DTC OUTPUT RECURS (DTC P0031, P0032 OR P101D)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the tester on.

    4. Clear the DTCs Click here.

    5. Start the engine.

    6. Allow the engine to idle for 1 minute or more.

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

    8. Read the DTCs.

      Result
      Result Proceed to
      DTC is not output A
      DTC P0031, P0032 or P101D is output B

    A

    CHECK FOR INTERMITTENT PROBLEMS Click here

    B

    REPLACE ECM Click here

  5. INSPECT NO. 1 INTEGRATION RELAY (EFI MAIN)


    1. Inspect the No. 1 integration relay (EFI MAIN) Click here.


    NG

    REPLACE NO. 1 INTEGRATION RELAY Click here

    OK

  6. CHECK HARNESS AND CONNECTOR (NO. 1 INTEGRATION RELAY - AIR FUEL RATIO SENSOR AND BODY GROUND)


    1. Disconnect the air fuel ratio sensor connector.

    2. Remove the No. 1 integration relay from the engine room main relay block.

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

      Standard Resistance (Check for Open)
      Tester Connection Condition Specified Condition
      B39-2 (+B) - 1E-4 Always Below 1 Ω
      1E-10 - Body ground Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      B39-2 (+B) or 1E-4 - Body ground Always 10 kΩ or higher

    4. Reconnect the air fuel ratio sensor connector.

    5. Reinstall the No. 1 integration relay.


    OK

    CHECK ECM POWER SOURCE CIRCUIT Click here

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR