SFI SYSTEM, Diagnostic DTC:P0037, P0038

DTC Code DTC Name
P0037 Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 2)
P0038 Oxygen Sensor Heater Control Circuit High (Bank 1 Sensor 2)

DESCRIPTION

A three-way catalytic converter is used in order to convert the carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxide (NOx) into less harmful substances. To allow the three-way catalytic converter to function effectively, it is necessary to keep the air fuel ratio of the engine near 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, and detects the oxygen concentration in the exhaust gas. Since the sensor is integrated with the 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 becomes rich. The heated oxygen sensor informs the ECM that the post-three-way catalytic converter air fuel ratio is lean (low voltage, i.e. less than 0.45 V).

Conversely, when the air fuel ratio is richer than the stoichiometric air fuel level, the oxygen concentration in the exhaust gas becomes lean. The heated oxygen sensor informs the ECM that the post-three-way catalytic converter air fuel ratio is rich (high voltage, i.e. more 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 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 the primary air fuel ratio control.

A01CCOEE01

Tech Tips


  • Sensor 2 refers to the sensor mounted behind the three-way catalytic converter and located far from the engine assembly.

  • When any of these DTCs are set, the ECM enters fail-safe mode. The ECM turns off the heated oxygen 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 heated oxygen sensor heater circuit uses a relay on the +B side of the circuit.

    A01CG1PE07
for Models w/ CVT (w/o Euro-OBD)
DTC No. DTC Detection Condition Trouble Area
P0037

Heated oxygen sensor heater (sensor 2) current is less than 0.3 A

(1 trip detection logic)

  • Open in heated oxygen sensor heater (sensor 2) circuit

  • Heated oxygen sensor heater (sensor 2)

  • ECM
P0038

Heated oxygen sensor heater (sensor 2) current is more than 2 A

(1 trip detection logic)

  • Short in heated oxygen sensor heater (sensor 2) circuit

  • Heated oxygen sensor heater (sensor 2)

  • ECM
for Other Models
DTC No. DTC Detection Condition Trouble Area
P0037

Heated oxygen sensor heater (sensor 2) current is less than 0.3 A

(1 trip detection logic)

  • Open in heated oxygen sensor heater (sensor 2) circuit

  • Heated oxygen sensor heater (sensor 2)

  • ECM
P0038

Heated oxygen sensor heater (sensor 2) current is fail

(1 trip detection logic)

  • Short in heated oxygen sensor heater (sensor 2) circuit

  • Heated oxygen sensor heater (sensor 2)

  • ECM

Tech Tips


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

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

WIRING DIAGRAM

Refer to DTC P0136 Click here.

INSPECTION PROCEDURE

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. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. 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 HEATED OXYGEN SENSOR (HEATER RESISTANCE)


    1. A01CEV8E06
      Text in Illustration
      *1

      Component without harness connected

      (Heated Oxygen Sensor)

      Disconnect the heated oxygen sensor connector.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      1 (HT1B) - 2 (+B) 20°C (68°F) 11 to 16 Ω
      1 (HT1B) - 4 (E2) Always 10 kΩ or higher

    3. Reconnect the heated oxygen sensor connector.


    NG

    REPLACE HEATED OXYGEN SENSOR Click here

    OK

  2. CHECK TERMINAL VOLTAGE (+B OF HEATED OXYGEN SENSOR)


    1. A01CFXWE02
      Text in Illustration
      *1

      Front view of wire harness connector

      (to Heated Oxygen Sensor)

      Disconnect the heated oxygen sensor connector.

    2. Turn the engine switch on (IG).

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

      Standard Voltage
      Tester Connection Switch Condition Specified Condition
      D52-2 (+B) - Body ground Engine switch on (IG) 11 to 14 V

    4. Reconnect the heated oxygen sensor connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (HEATED OXYGEN SENSOR - EFI MAIN RELAY)

    OK

  3. 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 (Check for Open)
      Tester Connection Condition Specified Condition
      D52-1 (HT1B) - D41-47 (HT1B) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      D52-1 (HT1B) or D41-47 (HT1B) - Body ground Always 10 kΩ or higher

    4. Reconnect the heated oxygen sensor connector.

    5. Reconnect the ECM connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (HEATED OXYGEN SENSOR - ECM)

    OK

    REPLACE ECM Click here