Toyota P0031 Code HO2S Heater Control Circuit Low (Bank 1 Sensor 1)

By | March 1, 2024

Causes and Fixes Toyota P0031 OBDII Code

  • A Toyota P0031 Code is a “HO2S Heater Control Circuit Low (Bank 1 Sensor 1)”
  • Common causes include a bad oxygen sensor, or sensor wiring.
  • Symptoms include using more fuel than usual, check engine light, and bad acceleration.

A Toyota with a P0031 OBDII Code is having an issue with an Oxygen Sensor.

Oxygen sensors are located on the exhaust and monitor how much O2 has been burnt off in the engine and sometimes the catalytic converter.

What is a Toyota P0031 OBDII Code?

A Toyota P0031 Code is defined as a “HO2S Heater Control Circuit Low (Bank 1 Sensor 1)”

The error code means the computer (ECM/PCM) is seeing an issue with an O2 Sensor.

Oxygen sensors originally only gave information on the oxygen burnt off during combustion, but also can contain heat elements.

The heater sensor part of the oxygen sensor helps it to warm up more quickly than it otherwise would.

Early 02 sensors had no built in heater element and had to wait on the exhaust to heat up from the engine.

The heater element helps the O2 sensor to get accurate readings much quicker than it normally would and allows for better performance.

What is (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)

oyota P0031 OBDII Code
The (A/F) Sensor Heater is a part of the oxygen sensor that also contains a heat element to warm up the sensor quickly on cold starts.
Bank 1 is the side of the engine with the number-1 cylinder.

Sensor 1 is the first sensor on the exhaust on Bank 1.

Possible Causes Toyota P0031 OBDII Code

  • Bad Oxygen Sensor
  • Wiring Open or Short
  • Bad Harness Connection
  • Failed Relay or Fuse

How to Fix Toyota P0031 OBDII Code

  • Locate Bank 1 Sensor 1 Oxygen Sensor
  • O2 Sensor 06-11 Toyota Camry
    The first thing to do is locate the Bank 1 Sensor 1 Oxygen Sensor on the Toyota being worked on.

    There can be a difference between Toyota’s depending on the year and engine type.

    Finding a layout or diagram of the 02 sensors would be very helpful.

    If no layout can be found, locate Bank 1, which will be the number one cylinder.

    Follow the exhaust on Bank-1, and the first O2 sensor will be the one having the problem.

  • Check the 02 Sensor Harness and Wiring
  • O2 Sensor Wiring
    If the O2 sensor wiring has short or open, it can cause the same symptoms as a bad sensor.

    Check to be sure the harness is plugged all the way in, and the wiring all looks good.

  • Check for a Blown Fuse or Relay
  • The O2 sensor will usually have a fuse located in the engine compartment fuse box.

    If the fuse is blown, there will be no power to the circuit.

    Some Toyota’s also has a relay that will be in the same fuse box and is a part of the circuit.

  • Test Replace the Oxygen Sensor
  • 02 Sensor Removal
    If the wiring all looks good and there are no blown fuses, then the O2 sensor is very likely bad.

    It can be tested or replaced, with most replacing it since it is a low-cost part.

    The heater element can be tested with a multi meter for continuity.

Can You Drive a Toyota with P0031?

A Toyota with P0031 will very likely be drive-able but may have idling issues.

How badly the O2 sensor has failed will be directly related to how badly the engine runs.

Since the onboard computer uses the oxen sensor to know how much oxygen is being burnt off during combustion, it has a direct effect on the Air/Fuel ratio going into the engine.

If the sensor has only started to fail, the engine will likely run fine.

If the sensor has completely failed, the engine will likely begin to run badly.

Category: OBD OBDII Error Codes Toyota

About Bob Thomas

Bob Thomas is an automotive mechanic with 30 plus years experience. He is a contributor to several publications and has written many articles on automotive maintenance and repairs. He also has created many auto repair videos on YouTube.

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