EngineLightCodes
Powertrain code

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

Severity
Fix soon
Typical repair cost
$90–$390
Do it yourself
Possible, medium
Shop time
0.5–1.5 hours

The upstream oxygen sensor on bank 1 (sensor 1, before the catalytic converter) only delivers a usable signal once its ceramic element is hot.

How the engine computer detects it

A heating element inside the sensor gets it there quickly after a cold start. Typically the heater receives battery voltage via a fuse or relay, and the engine control module switches the ground side with a pulsed signal while comparing the commanded state with the measured voltage or current. P0031 means the control module measures too little voltage or current while the heater is switched on. Depending on the system this points to a burnt-out element, a missing supply or an interrupted control wire. The sensor then warms up late, so mixture control starts late and cold-start emissions rise.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Check engine light on
  • Closed-loop control starts late after a cold start
  • Further heater codes if a shared fuse has blown
  • Emissions test or readiness check failed

Common causes

  1. Heating element burnt out or high resistance (too little current) Most likely
  2. Supply wire interrupted or fuse blown Most likely
  3. Control wire to the engine control module interrupted Possible
  4. Corroded connector with high contact resistance Possible
  5. Output driver in the engine control module faulty Less likely

How to diagnose P0031

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: oxygen sensor upstream, oxygen sensor heater, oxygen sensor wiring, oxygen sensor heater fuse.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Vehicles that report P0031 most

VehicleYearsReportsMedian miles
Chevrolet Volt2016–20184—

Counts of owner complaints to the NHTSA that mention P0031 (7 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.

Reading the code

P
Powertrain
0
Generic (SAE) code
0
Fuel and air metering, auxiliary emission controls
31
Specific fault

Questions drivers ask

Can I drive with code P0031?

Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.

Will my car pass an emissions inspection with P0031?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Will P0031 clear by itself?

The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.

Can I fix P0031 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.

Often reported together

Codes that owners mention in the same NHTSA complaints as P0031. They can point to a shared cause, so it's worth checking them together.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.