P0031 – Meaning, Causes, Symptoms, & Fixes

Code P0031 Definition

HO2S Heater Control Circuit Low (Bank 1, Sensor 1)

What Does P0031 Mean?

The P0031 code is a result of the HO2S (heated oxygen sensors) incorrectly detecting the air to fuel ratio of the exhaust. This ratio is then sent to the ECM which uses this data along with comparisons to the outside air, to regulate the air to fuel ratio needed by the engine. In addition, this misreading may be the result of a bad heater element which if not operating, will trigger the P0031 code.

P0031 Symptoms*

*No noticeable adverse conditions in some cases

P0031 Cause

  • Frayed wiring/connectors
  • Short in heater circuit wiring
  • Faulty heated oxygen sensor
  • Malfunctioning PCM/ECM

Code P0031 Severity – Moderate 

This trouble code will not prevent your vehicle from running. The most common result(s) are failure of the sensor loop, lower fuel economy, and poor vehicle operation. However, if left unsolved, this code could increase the likelihood of your vehicle running rough and cause potential damage to other components of your vehicle.

Code P0031 Common Diagnosis Mistakes

Prematurely replacing the heated oxygen sensor(s) before attempting to visually inspect the wiring around the oxygen sensor(s) for chafed/frayed wiring.

P0031 Diagnosis

  • Tools Needed to Diagnose:

Difficulty of Diagnosis and Repair – (1-6)

  1. Check to see if there are any other codes along with P0031 and clear your Check Engine Light with FIXD.
  2. Check the freeze frame data and fuel gauge to pinpoint the issue.
  3. Conduct a visual inspection of wiring around the heated oxygen sensor(s) for fraying or disconnection.
  4. Check the ground circuit for continuity
  5. With the engine off and the key selecting “on”, use a voltmeter to check for atleast 12 volts. If no voltage is registered, consider repairing short in heater circuit wiring.
  6. If the voltmeter registers 12 volts, consider replacing the heated oxygen sensor.

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Comments 2


May 22, 2019


Ricky F Rhodes

August 7, 2019

I think this is a factor but not sure if this is exactly the problem. I change the motor in this Ion. And man it fired right up.as if it just run out of gas.. And I was happy to know I got a good motor but then I had starter problems. And I replaced it and I wired it up but I had the ground wire on where it should have been the alternator.. But it didn’t take long cause it just was clicking when I truned the key as before it was starting up no problem.. But then it happened. Went to start it and it was nothing just the ring of the ignition and door bells… Lol. No start no nothing.. What would you think happened.. Is the security styem locked.?
Cause I had it turn over a couple times and it sounded like no fuel is getting their and no fire.. And the security lights is coming on but it goes off It’s a yellow sign with a lock and a car . And it’s sales locked.. Pls help if you can. Don’t know what else to do. Thanks.

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