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 P0031 OBDII error code means the onboard computer (ECM) is seeing an issue with an O2 Sensor.
Oxygen sensors originally only gave information on the oxygen burnt off during combustion, but now often also contain heat sensors.
The heat sensors monitor the catalytic converter since a catalytic gives off more heat when it fails.
What is (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
The (A/F) Sensor Heater is a part of the oxygen sensor that also contains a heat sensor to monitor the catalytic converter.
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
- Check the 02 Sensor Harness and Wiring
- Check for a Blown Fuse or Relay
- Replace the Oxygen Sensor
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.
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.
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.
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.
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.