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### DTC P0031 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)

### DTC P0032 Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)

### DTC P0051 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1)

### DTC P0052 Oxygen (A/F) Sensor Heater Control Circuit High (Bank 2 Sensor 1)

## for Preparation Click here

## DESCRIPTION

Refer to DTC P2195 (Click here).

HINT:

1. 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 OFF.
2. The ECM uses 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.

DTC No. | DTC Detection Condition | Trouble Area

P0031
P0051

Heated current is 0.8 A or less when heater operates (bank 1)
(1 trip detection logic)

1. Open or short in A/F sensor heater (bank 1 sensor 1) circuit
2. A/F sensor heater (bank 1 sensor 1)
3. A/F relay
4. ECM

P0032
P0052

Heated current exceeds 10 A when heater operates (bank 2)
(1 trip detection logic)

1. Open or short in A/F sensor heater (bank 2 sensor 1) circuit
2. A/F sensor heater (bank 2 sensor 1)
3. A/F relay
4. ECM

HINT:

1. Bank 1 refers to the bank that includes the No. 1 cylinder.
2. Bank 2 refers to the bank that does not include the No. 1 cylinder.
3. Sensor 1 refers to the sensor closest to the engine assembly.
4. Sensor 2 refers to the sensor farthest away from the engine assembly.

## MONITOR DESCRIPTION

The ECM uses A/F sensor information to keep the air-fuel ratio close to the stoichiometric ratio. This maximizes the catalytic converter's ability to purify exhaust gases. The sensor detects oxygen levels in the exhaust gas and sends this signal to the ECM.
The inner surface of the sensor element is exposed to outside air. The outer surface of the sensor element is exposed to 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 concentration of the exhaust and outside air. The platinum coating amplifies the voltage generation. When the sensor is heated, the sensor becomes very efficient. If the temperature of the exhaust is low, the sensor will not generate useful voltage signals without supplemental heating. The ECM regulates the supplemental heating using a duty-cycle approach to regulate the average current in the heater element.
If the heater current is out of the normal operating range, the sensor's output signals will be inaccurate and the ECM cannot regulate the A/F properly.
When the heater current is out of the normal operating range, the ECM interprets this as a malfunction and sets a DTC.

## WIRING DIAGRAM

Refer to DTC P2195 (Click here).

## INSPECTION PROCEDURE

HINT:

1. Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, 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.
2. Although "oxygen sensor" is in the DTC titles, these DTCs are related to the air-fuel ratio (A/F) sensor.
3. Sensor 1 refers to the sensor mounted before the Three-Way Catalytic Converter (TWC) and is located near the engine assembly.
4. Sensor 2 refers to the sensor mounted after the TWC and is located far from the engine assembly.

1.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

1. Disconnect the A/F sensor connector.

1. Measure the resistance of the A/F sensor.

   Standard resistance:

     Tester Connection | Condition | Specified Condition
     1 (HT) - 2 (+B) | 20°C (68°F) | 1.8 to 3.4 Ω
     1 (HT) - 4 (AF-) | - | 10 kΩ or higher

| NG |

REPLACE AIR FUEL RATIO SENSOR

OK |

2.INSPECT RELAY (Marking: A/F)

1. Remove the A/F heater relay from the engine room relay block.

1. Measure the resistance of the relay.

   Standard resistance:

     Terminal No. | Specified Condition
     3 - 5 | 10 kΩ or higher
     3 - 5 | Below 1 Ω (when battery voltage is applied to terminals 1 and 2)

| NG |

REPLACE RELAY

OK |

3.INSPECT ECM (HA1A AND HA2A VOLTAGE)

1. Turn the ignition switch ON.

1. Measure the voltage of the E16 and E17 ECM connectors.

   Standard voltage:

     Tester Connection | Specified Condition
     E16-2 (HA1A) - E17-1 (E1) | 9 to 14 V
     E16-1 (HA2A) - E17-1 (E1) | 9 to 14 V

| OK |

REPLACE ECM

NG |

4.CHECK WIRE HARNESS (A/F SENSOR - ECM AND A/F RELAY)

1. Disconnect the A18 and A25 A/F sensor connectors.

1. Disconnect the E16 ECM connector.

1. Remove the A/F relay from the engine room relay block.

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

   Standard resistance (Bank 1 Sensor 1):

     Tester Connection | Specified Condition
     A18-1 (HT) - E16-2 (HA1A) | Below 1 Ω
     A18-2 (+B) - Relay block A/F relay terminal 5 | Below 1 Ω
     A18-1 (HT) or E16-2 (HA1A) - Body ground | 10 kΩ or higher
     A18-2 (+B) or relay block A/F relay terminal 5 - Body ground | 10 kΩ or higher

   Standard resistance (Bank 2 Sensor 1):

     Tester Connection | Specified Condition
     A25-1 (HT) - E16-1 (HA2A) | Below 1 Ω
     A25-2 (+B) - Relay block A/F relay terminal 5 | Below 1 Ω
     A25-1 (HT) or E16-1 (HA2A) - Body ground | 10 kΩ or higher
     A25-2 (+B) or relay block A/F relay terminal 5 - Body ground | 10 kΩ or higher

| NG |

REPAIR OR REPLACE HARNESS AND CONNECTOR

OK |

REPLACE ECM