P0031

HO2S Heater Control Circuit Low Bank 1 Sensor 1

Emissions / O2 sensor Generic OBD-II Medium

What it means

P0031 means the heater circuit for the upstream (bank 1, sensor 1) oxygen sensor is reading low voltage — usually a short to ground, an open, or a failed heater element inside the sensor. The heater brings the O2 sensor to operating temperature quickly; when it fails, closed-loop fuel control is delayed but the engine still runs normally.

Medium

Can I keep driving? Safe to drive short-term — no immediate mechanical risk, but it will fail an emissions test and slightly hurt cold-start economy.

Real-world scan data

Seen in

6,114

scans in the past year

Found in

1.0%

of scans

1.7%

of scans that found faults

Appears alongside · share of P0031 scans

P0037in 12.4% of scans

P0113in 11.5% of scans

C1122in 9.8% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Check-engine light on
Slightly worse cold-start fuel economy
Delayed closed-loop fuel control after start-up
Failed emissions test

Common causes

Most likely first

Failed heater element inside the O2 sensor (most common)Likely
Short to ground or open in the heater wiringCommon
Blown heater fuse or poor groundCommon
Corroded or loose connector at the sensorLess often
Failed PCM driver (rare)Less often

How to diagnose & fix

Work through it in order

Scan and record freeze-frame data.
Check the O2 sensor heater fuse.
Inspect the connector and wiring for a short to ground or an open.
Measure the heater element's resistance across the sensor terminals against spec.
Replace the O2 sensor if the heater is open or out of spec; consider the PCM last. Clear and re-test.

FAQ

Quick answers

Is it safe to drive with P0031?+

Yes, short-term. The heater only speeds up sensor warm-up, so there's no mechanical danger, but the car will fail emissions and warm-up fueling is slightly less efficient.

Can I just clear P0031?+

It comes back within a drive cycle or two until the heater or wiring is fixed. A failed heater element usually means replacing the O2 sensor.

Read & clear P0031 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX