Troubleshooting

DTC P0031 OXYGEN (A/F) SENSOR HEATER CONTROL CIRCUIT LOW (BANK 1 SENSOR 1)

HINT: This DTC is related to the A/F sensor, although the caption is oxygen sensor.

CIRCUIT DESCRIPTION

DTC Detection Condition:

The A/F sensors is the planar type. Compared to the conventional type, the sensor and heater portions are narrower overall. Because the heat of the heater is conducted through the alumina to zirconia (of the sensor portion) it accelerates the activation of the sensor.

To obtain a high purification rate of the CO, HC and NOx components of 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 air fuel ratio.

The A/F sensor has the characteristic that it provides output voltage* being approximately proportional to the existing air fuel ratio. The A/F sensor output voltage* is used to provide feedback for the ECM to control the air fuel ratio.

By the A/F sensor output, the ECM can determine the deviation amount from the stoichiometric air fuel ratio and control the proper injection time immediately. If the A/F sensor is out of order, ECM is unable to perform the accurate air fuel ratio control.

The A/F sensor is equipped with a heater which heats the zirconia element. The heater is controlled by the ECM. When the intake air volume is low (the temperature of the exhaust gas is low), the current flows to the heater to heat the sensor for the accurate oxygen concentration detection.

*: The voltage value changes at the inside of the ECM only.

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

HINT:
- Bank 1 refers to the bank that includes cylinder No.1.
- Bank 2 refers to the bank that does not include cylinder No.1.
- 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:

Step 1 - 2:

Step 3:

Step 4:

INSPECTION PROCEDURE

HINT: Read freeze frame data using the hand-held tester or the OBD II scan tool, as freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.