GSIC - Global Service Information Center

### DTC P0037 Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 2)

### DTC P0038 Oxygen Sensor Heater Control Circuit High (Bank 1 Sensor 2)

## for Preparation Click here

HINT:

1. Sensor 1 refers to the sensor mounted before the Three-Way Catalytic Converter (TWC) and is located near the engine assembly.
2. Sensor 2 refers to the sensor mounted after the TWC and is located far from the engine assembly.

## DESCRIPTION

Refer to DTC P0136 (Click here).

HINT:

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

DTC No. | DTC Detection Condition | Trouble Area

P0037

Heated current is 0.3 A or less when heater operates
(1 trip detection logic)

1. Open in heater circuit of heated oxygen sensor
2. Heated oxygen sensor heater
3. MAIN relay
4. ECM

P0038

Heated current exceeds 2 A when heater operates
(1 trip detection logic)

1. Short in heater circuit of heated oxygen sensor
2. Heated oxygen sensor heater
3. MAIN relay
4. ECM

## MONITOR DESCRIPTION

The sensing portion of the heated oxygen sensor has a zirconia element which is used to detect oxygen concentration in the exhaust. If the zirconia element is at the proper temperature and the difference of the oxygen concentration between the inside and outside surface of the sensor is large, the zirconia element will generate voltage signals. In order to increase the oxygen concentration detecting capacity in the zirconia element, the ECM supplements the heat from the exhaust with the heat from the heating element inside the sensor. When current in the sensor is out of the standard operating range, the ECM interprets this as a fault in the heated oxygen sensor and sets a DTC.
Example:
The ECM will set a high-current DTC if the current in the sensor is more than 2 A when the heater is OFF. Similarly, the ECM will set a low-current DTC if the current is less than 0.25 A when the heater is ON.

## WIRING DIAGRAM

Refer to DTC P0136 (Click here).

## INSPECTION PROCEDURE

HINT:

  Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions 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.

1.INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE)

1. Disconnect the H7 sensor connector.

1. Measure the resistance of the heated oxygen sensor.

   Standard:

     Tester Connection | Condition | Specified Condition
     1 (HT) - 2 (+B) | 20°C (68°F) | 11 to 16 Ω
     1 (HT) - 4 (E) | Always | 10 kΩ or higher

| NG |

REPLACE HEATED OXYGEN SENSOR

OK |

2.INSPECT INTEGRATION RELAY (MAIN RELAY)

1. Remove the integration relay from the engine room junction block.

1. Measure the voltage of the MAIN relay.

   Standard:

     Tester Connection | Condition | Specified Condition
     1J-5 - Body ground | Ignition switch ON | 10 to 14 V

| NG |

REPLACE INTEGRATION RELAY

OK |

3.INSPECT ECM (HT1B VOLTAGE)

1. Turn the ignition switch ON.

1. Measure the voltage of the E12 ECM connector.

   Standard voltage:

     Tester Connection | Specified Condition
     E12-2 (HT1B) - E11-3 (E1) | 9 to 14 V

| OK |

REPLACE ECM

NG |

4.CHECK WIRE HARNESS (HEATED OXYGEN SENSOR - ECM AND INTEGRATION RELAY)

1. Disconnect the H7 sensor connector.

1. Disconnect the E12 ECM connector.

1. Disconnect the 1J connector from the engine room junction block.

1. Measure the resistance of the wire harness side connectors.

   Standard resistance:

     Tester Connection | Specified Condition
     H7-1 (HT) - E12-2 (HT1B) | Below 1 Ω
     H7-2 (+B) - 1J-5 | Below 1 Ω
     H7-1 (HT) or E12-2 (HT1B) - Body ground | 10 kΩ or higher
     H7-2 (+B) or 1J-5 - Body ground | 10 kΩ or higher

| NG |

REPAIR OR REPLACE HARNESS AND CONNECTOR

OK |

REPLACE ECM