SFI SYSTEM, Diagnostic DTC:P0031, P0032, P0051, P0052

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)
P0051 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1)
P0052 Oxygen (A/F) Sensor Heater Control Circuit High (Bank 2 Sensor 1)

DESCRIPTION

Tech Tips


  • Although the DTC titles include 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 and located near the engine assembly.

The air fuel ratio sensor generates 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 level, 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 the planar type and is integrated with the 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 into the heater to heat the sensor, in order to facilitate accurate oxygen concentration detection. In addition, the sensor and heater portions are narrower than the conventional type. The heat generated by the heater is conducted to the solid electrolyte though the alumina, therefore the sensor activation is accelerated.

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 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 level.

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

A0161LRE08

Tech Tips


  • When any of these DTCs are set, the ECM enters fail safe mode. The ECM turns off the air fuel ratio sensor heater in fail safe mode. Fail-safe mode continues until the engine 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.

    A015YTYE39
DTC No. DTC Detection Condition Trouble Area

P0031

P0051

 Air fuel ratio sensor heater (bank 1 sensor 1) current less than 0.8 A (1 trip detection logic)

  • Open in air fuel ratio sensor heater (bank 1, 2 sensor 1) circuit

  • Air fuel ratio sensor heater (bank 1, 2 sensor 1)

  • A/F fuse

  • Engine room No. 2 junction block

  • ECM

P0032

P0052

 Air fuel ratio sensor heater (bank 2 sensor 1) current more than 10 A (1 trip detection logic)

  • Short in air fuel ratio sensor heater (bank 1, 2 sensor 1) circuit

  • Air fuel ratio sensor heater (bank 1, 2 sensor 1)

  • A/F fuse

  • Engine room No. 2 junction block

  • ECM

Tech Tips


  • Bank 1 refers to the bank that includes No. 1 cylinder.

  • Bank 2 refers to the bank that does not include No. 1 cylinder.

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

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

MONITOR DESCRIPTION


  1. 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 to purify the exhaust gases.

  2. 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.

  3. 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.

  4. 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 will be inaccurate, as a result, the ECM will be unable to regulate air fuel ratio properly.

  5. 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 sets a DTC.


    • Example:


      • The ECM sets DTC P0032 or P0052 when the current in the air fuel ratio sensor heater is more than 10 A. Conversely, when the heater current is less than 0.8 A, DTC P0031 or P0051 is set.

WIRING DIAGRAM

Refer to DTC P2195 Click here.

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.

PROCEDURE


  1. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. A015ZERE23

      Disconnect the air fuel ratio sensor connector.

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

      Standard Resistance (Bank 1 Sensor 1)
      Tester Connection Condition Specified Condition
      1 (HA1A) - 2 (+B) 20°C (68°F) 1.8 to 3.4 Ω
      1 (HA1A) - 4 (A1A-) Always 10 kΩ or higher
      Standard Resistance (Bank 2 Sensor 1)
      Tester Connection Condition Specified Condition
      1 (HA2A) - 2 (+B) 20°C (68°F) 1.8 to 3.4 Ω
      1 (HA2A) - 4 (A2A-) Always 10 kΩ or higher

    3. Reconnect the air fuel ratio sensor connector.


    NG

    REPLACE AIR FUEL RATIO SENSOR Click here

    OK

  2. CHECK TERMINAL VOLTAGE (+B OF AIR FUEL RATIO SENSOR)


    1. A016298E22

      Disconnect the air fuel ratio sensor connector.

    2. Turn the engine switch on (IG).

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

      Standard Voltage (Bank 1 Sensor 1)
      Tester Connection Switch Condition Specified Condition
      E42-2 (+B) - Body ground Engine switch on (IG) 11 to 14 V
      Standard Voltage (Bank 2 Sensor 1)
      Tester Connection Switch Condition Specified Condition
      E38-2 (+B) - Body ground Engine switch on (IG) 11 to 14 V

    4. Reconnect the air fuel ratio sensor connector.


    NG

    CHECK HARNESS AND CONNECTOR (A/F RELAY - AIR FUEL RATIO SENSOR)) Click here

    OK

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


    1. A015ZLVE04

      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)
      Tester Connection Condition Specified Condition
      E42-1 (HA1A) - E6-5 (HA1A) Always Below 1 Ω
      E38-1 (HA2A) - E6-6 (HA2A) Always Below 1 Ω
      E6-4 (E04) - Body ground Always Below 1 Ω
      E5-1 (E05) - Body ground Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      E42-1 (HA1A) or E6-5 (HA1A) - Body ground Always 10 kΩ or higher
      E38-1 (HA2A) or E6-6 (HA2A) - 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 (AIR FUEL RATIO SENSOR - ECM)

    OK

    REPLACE ECM Click here

  4. CHECK HARNESS AND CONNECTOR (A/F RELAY - AIR FUEL RATIO SENSOR))


    1. A015ZCRE03

      Disconnect the air fuel ratio sensor connector.

    2. Remove the A/F relay from the engine room No. 2 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
      E42-2 (+B) - A/F relay (3) Always Below 1 Ω
      E38-2 (+B) - A/F relay (3) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      E42-2 (+B) or A/F relay (3) - Body ground Always 10 kΩ or higher
      E38-2 (+B) or A/F relay (3) - Body ground Always 10 kΩ or higher

    4. Reinstall the A/F relay.

    5. Reconnect the air fuel ratio sensor connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - A/F RELAY)

    OK

  5. INSPECT A/F RELAY


    1. A0161LXE03

      Remove the A/F relay from the engine room No. 2 relay block.

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

      Standard Resistance
      Tester Connection Switch Condition Specified Condition
      3 - 5 When no battery voltage applied to terminals 1 and 2 10 kΩ or higher
      3 - 5 When battery voltage applied to terminals 1 and 2 Below 1 Ω

    3. Reinstall the A/F relay.


    NG

    REPLACE A/F RELAY

    OK

  6. CHECK HARNESS AND CONNECTOR (A/F RELAY - BODY GROUND)


    1. A0163CCE01

      Remove the A/F relay from the engine room No. 2 relay block.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      A/F relay (2) - Body ground Always Below 1 Ω

    3. Reinstall the A/F relay.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F RELAY - BODY GROUND)

    OK

  7. CHECK HARNESS AND CONNECTOR (A/F RELAY POWER SOURCE)


    1. A0163CCE01

      Remove the A/F relay from the engine room No. 2 relay block.

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

      Standard Voltage
      Tester Connection Switch Condition Specified Condition
      A/F relay (5) - Body ground Always 11 to 14 V

    3. Reinstall the A/F relay.


    NG

    INSPECT FUSE (A/F FUSE) Click here

    OK

  8. INSPECT FUSE (EFI NO. 2 FUSE)


    1. A015YXDE06

      Remove the EFI No. 2 fuse from the engine room No. 2 relay block.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      EFI No. 2 fuse Always Below 1 Ω

    3. Reinstall the EFI No. 2 fuse.


    NG

    REPLACE FUSE (EFI NO. 2 FUSE)

    OK

    REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F RELAY - INTEGRATION RELAY)

  9. INSPECT FUSE (A/F FUSE)


    1. A015YXDE15

      Remove the A/F fuse from the engine room No. 2 relay block.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      A/F fuse Always Below 1 Ω

    3. Reinstall the A/F fuse.


    NG

    REPLACE FUSE (A/F FUSE)

    OK

    REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F RELAY - BATTERY)