If you have a vehicle that is giving a P0031 error code, there is a problem with an upstream sensor on the exhaust.
Fixing a P0031 error code falls into the DIY mechanic job, with many at-home backyard mechanics solving the issue.
Of course, if in doubt, be sure to take your vehicle to a professional.
What is a P0031 Error Code?
A P0031 is an Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 1).
The sensor is an Air Fuel Ratio or O2 Sensor located on Bank 1 of the engine and Sensor 1, which is the upstream sensor.
Bank 1 on an engine is always the side with cylinder-1. A V6 or V8 engine will have 2-banks, while a 4-cylinder engine will only have 1-bank.
Sensor 1 is on the exhaust and always the one before the catalytic converter.
There is also a Sensor 2, which is called downstream and is always located after the catalytic converter.
While the onboard computer (ECM) is seeing an issue with the sensor, other things can also cause the sensor to not work, such as a fuse, relay, or wiring.
3 Causes and Fixes P0031 Error Code
- Fuse or Relay
- Air Fuel Ratio or O2 Sensor
- Wiring
A bad fuse or relay can cause an issue with a sensor not working properly.
For example, a 2004 Toyota Tacoma uses the A/F Heater relay in a circuit with the Air Fuel Ratio or O2 Sensors.
If this relay goes bad, a P0031 error code will come on.
Check the fuses and relays along with a circuit diagram for your vehicle.
An Air Fuel Ratio O2 Sensor is a more advanced O2 Sensor that does basically the same thing.
Both are used to give data to the computer on the air-fuel ratio so it can adjust as needed.
A bad Air Fuel Ratio sensor is a common problem with a P0031 error code, and often the first thing replaced.
The sensor to replace with a P0031 will be the Bank 1 Sensor 1.
Bank 1 on an engine is always the side with the number 1 cylinder, and sensor 1 is always the first sensor before the catalytic converter.
If you have a V6 or V8 engine, the number 1 cylinder will be important to get Bank-1, while a 4-cylinder engine will have only one upstream sensor.
Sensor 1 is sometimes called upstream since it will be located before the catalytic converter, while sensor 2 is after and often called downstream.
A bad wire or connection can cause issues.
For example, I have seen a Nissan that had a P0031 error, so the Air Fuel Ratio Sensor was swapped out, but the error did not clear.
After reading voltage at the sensor wire harness, one wire which was supposed to have a steady 12-volt reading had no voltage.
All the fuses tested good, so the wiring was looked at next which a bad wire connection was found in the bottom of the fuse box.
This is an extreme example but something to keep in mind usually when all other things has been checked and tested.
How Much Does It Cost to Repair a P0031 Error Code?
The cost for a shop to repair a P0031 error code will vary between $500-$1000 but can be more or less depending on the problem and the car.
If a sensor is bad, the replacement cost range roughly from $20-$150, with some vehicle parts costing less than others.
If there is a problem with the wiring, the cost can go up since more troubleshooting time will be needed and cost more.
A new Air Fuel Ratio or O2 Sensor cost can be looked up online for your vehicle to get a rough idea of cost.
Summary
If your car or truck has a P0031 error code, the onboard computer (ECM) is reading a problem with the Bank 1 upstream sensor.
The sensor is located on the exhaust, with Sensor 1 located before the catalytic converter.
Wiring can also be an issue with a bad connection or fuse, causing the sensor to not work.
Troubleshooting the P0031 code is usually straightforward but can be more involved if there is a wiring problem.
The most common solution is to replace the Bank 1 Sensor 1.
Have you had a problem with a P0031 error code? Let us know your thoughts below.