P0031: HO2S Heater Control Circuit Low Bank 1 Sensor 1
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Yes - no drivability risk, just slower warm-up of fuel control.
Symptoms
- Check engine light
- Marginally higher fuel use
- Emissions monitors not completing
Likely causes, most common first
- Heater circuit shorted to ground
- Heater element failed with low resistance
- Chafed harness near the exhaust
- Corroded connector pins
Read P0031 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0031 says the bank 1 upstream heater circuit reads low - the electrical signature of a short to ground or a heater element that has failed internally. The computer measures heater current every drive cycle, which is why this code appears promptly rather than after weeks of degradation.
A useful check before buying a sensor: measure the heater's resistance across its two heater pins at the connector. Most read somewhere between 3 and 15 ohms cold, and the specification is in the service data. A reading near zero confirms the element; a normal reading sends you to the harness, which on this sensor runs close to hot exhaust parts and chafes more often than most.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P0031
“Vsc and vsc of lights are oncodes c1223 ABS control system malfunction, c1231 steering angle sensor, and c1247 stroke sensor indicates needs the skid control ecu t 2.0 replaced skid control ecu 08/01/2010 check engine light found p0031 af sensor b1s1 t1.0 parts replaced. 6/01/2013 again vsc trac off service engine light on and dealership wants 1400.00 for new computer. *tr”2003 Toyota Sequoia · Jan 2010 · 66,253 mi
“The engine light won't go out there is a error reading of p0031 on the o2 sensor been replace 7 to 10 times and the light still stays on even resetting.I have problems year after year with my brakes over all I lost total trust in toyota corolla plus a lot more problems toyota takes forever to send out the recall letters. I have 8 recalls but when you go look it up its states no recalls well this is why I lost trust toyota doesn't care they use to be the best car ever not anymore.”2006 Toyota Corolla · Apr 2009 · 156,000 mi
Cars that report P0031 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0031?
Yes - no drivability risk, just slower warm-up of fuel control.
How much does it cost to fix P0031?
Typical US repair costs range from $80 for the simplest fix (upstream oxygen sensor) to $450 in the worst case. The right number depends on which cause your car has - see the causes list.
Related codes
The codes closest to P0031. They often appear together, and telling them apart is usually what narrows the diagnosis.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.