SFI SYSTEM (w/ Secondary Air Injection System), Diagnostic DTC:P0031, P0032

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)

DESCRIPTION

Tech Tips


  • Although the DTC titles say the oxygen sensor, these DTCs relate to the Air-Fuel Ratio (A/F) sensor.

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

Refer to DTC P2195 Click here.

Tech Tips


  • When any of these DTCs are set, the ECM enters fail-safe mode. The ECM turns off the A/F sensor heater in fail-safe mode. Fail-safe mode continues until the ignition switch is turned to OFF.

  • The ECM provides a pulse width modulated control circuit to adjust the current through the heater. The A/F sensor heater circuit uses a relay on the +B side of the circuit.

A01BI28E04
DTC No. DTC Detection Conditions Trouble Areas
P0031

Air-Fuel Ratio (A/F) sensor heater current less than 0.8 A

(1 trip detection logic)

  • Open in A/F sensor heater circuit

  • A/F sensor heater

  • Integration relay (A/F HEATER relay)

  • ECM
P0032

Air-Fuel Ratio (A/F) sensor heater current more than 10 A

(1 trip detection logic)

  • Short in A/F sensor heater circuit

  • A/F sensor heater

  • Integration relay (A/F HEATER relay)

  • ECM

MONITOR DESCRIPTION

The ECM uses information from the Air-Fuel Ratio (A/F) 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 A/F 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 A/F 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 A/F sensor will be inaccurate, as a result, the ECM will be unable to regulate air-fuel ratio properly.

When the current in the A/F 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 when the current in the A/F sensor heater is more than 10 A. Conversely, when the heater current is less than 0.8 A, DTC P0031 is set.

WIRING DIAGRAM

Refer to DTC P2195 Click here.

INSPECTION PROCEDURE

Tech Tips

Read freeze frame data using an intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air-fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.

PROCEDURE


  1. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. A01BEQSE27

      Disconnect the D33 Air-Fuel Ratio (A/F) sensor connector.

    2. Measure the resistance between the terminals of the A/F sensor connector.

      Resistance
      Tester Connections Specified Conditions
      HA1A (1) - +B (2) 1.8 Ω to 3.4 Ω at 20°C (68°F)
      HA1A (1) - A1A- (4) 10 kΩ or higher

    3. Reconnect the A/F sensor connector.


    NG

    REPLACE AIR FUEL RATIO SENSOR

    OK

  2. INSPECT INTEGRATION RELAY (A/F HEATER RELAY)


    1. Remove the integration relay from the engine room R/B No.1.

    2. A01BH79E01

      Check the integration relay (A/F HEATER relay).

      Resistance
      Tester Connections Specified Conditions
      A1 - C4 10 kΩ or higher
      A1 - C4

      Below 1 Ω

      (when battery voltage applied to terminals C2 and C3)

    3. Reinstall the integration relay.


    NG

    REPLACE INTEGRATION RELAY

    OK

  3. INSPECT ECM


    1. A01BDNSE21

      Turn the ignition switch to the ON position.

    2. Measure the voltage between the terminals of the D1 and D3 ECM connector.

      Voltage
      Tester Connections Specified Conditions
      HA1A (D1-1) - E04 (D3-7) 9 to 14 V

    NG

    CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM, A/F SENSOR - INTEGRATION RELAY) Click here

    OK

    REPLACE ECM

  4. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM, A/F SENSOR - INTEGRATION RELAY)


    1. A01BHVDE01

      Check the harness and connectors between the ECM and A/F sensor.


      1. Disconnect the D33 A/F sensor connector.

      2. Disconnect the D1 ECM connector.

      3. Measure the resistance.

        Resistance (Check for open)
        Tester Connections Specified Conditions
        HA1A (D33-1) - HA1A (D1-1) Below 1 Ω
        Resistance (Check for short)
        Tester Connections Specified Conditions
        HA1A (D33-1) or HA1A (D1-1) - Body ground 10 kΩ or higher

      4. Reconnect the A/F sensor connector.

      5. Reconnect the ECM connector.

    2. Check the harness and connector between the A/F sensor and integration relay.


      1. Disconnect the D33 A/F sensor connector.

      2. Disconnect the integration relay connector.

      3. Measure the resistance.

        Resistance (Check for open)
        Tester Connections Specified Conditions
        +B (D33-2) - Integration relay (C4) Below 1 Ω
        Resistance (Check for short)
        Tester Connections Specified Conditions

        +B (D33-2) or Integration relay (C4)

        - Body ground

        		 10 kΩ or higher

      4. Reconnect the A/F sensor connect.

      5. Reconnect the integration relay connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

    REPLACE ECM