P0031
HO2S Heater Control Circuit Low (Bank 1 Sensor 1)
The engine computer sees a problem in the heater for the front oxygen sensor on bank 1. The heater helps the sensor warm up quickly so fuel control works correctly. A low heater circuit signal usually means a wiring, fuse, relay, or sensor problem.
- SEV
- 3/5
- DRIVE
- CAUTION
- DIY
- $15–$150
- SHOP
- $120–$450
Quick answer
AI-CITATION READYWhat it means
Can you drive with it?
Most common causes
- Failed Bank 1 Sensor 1 oxygen sensor heater element
- Blown fuse, bad relay, or poor power supply to the heater circuit
- Damaged, corroded, or loose wiring/connectors near the upstream oxygen sensor
Typical repair cost
DIY usually runs $15–$150. Typical shop repair lands around $120–$450, depending on the root cause.
01 / Definition
P0031 sets when the PCM detects a low voltage condition in the heated oxygen sensor heater control circuit for Bank 1 Sensor 1. This is the upstream sensor on the bank that contains cylinder 1. The fault can be caused by an open heater circuit, a short to ground, damaged wiring, blown fuse, bad relay, or a failed oxygen sensor heater element.
02 / Drive status
With caution. The vehicle may still run, but fuel economy, emissions, and cold-start operation can suffer. Diagnose it soon because related wiring or sensor faults can get worse.
03 / Symptoms
- Check engine light
- Reduced fuel economy
- Rough running during cold starts
- Failed emissions test
- Delayed closed-loop operation
- Possible related oxygen sensor codes
04 / Causes
| 1 | Failed Bank 1 Sensor 1 oxygen sensor heater element | high |
|---|---|---|
| 2 | Blown fuse, bad relay, or poor power supply to the heater circuit | high |
| 3 | Damaged, corroded, or loose wiring/connectors near the upstream oxygen sensor | high |
| 4 | Short to ground in the heater control circuit | medium |
| 5 | Faulty PCM driver or control circuit issue | low |
05 / Diagnostic sequence
- 01Check for other codes, especially oxygen sensor, heater, power supply, or fuel trim codes.
- 02Inspect the Bank 1 Sensor 1 connector and wiring for heat damage, corrosion, broken locks, or melted insulation.
- 03Check the heater fuse and relay with a test light or multimeter.
- 04Verify battery voltage and heater power supply at the sensor connector with the key on.
- 05Measure heater resistance at the sensor and compare it to service specifications.
- 06Check the control side of the circuit for short to ground or open wiring.
- 07If power, ground, and wiring are correct, replace the oxygen sensor and retest.
- 08If the code returns after sensor replacement, test the PCM control circuit and connector pins.
06 / Repairs
| 1 | Repair damaged wiring, terminals, or connectors in the Bank 1 Sensor 1 heater circuit | $15–$120 |
|---|---|---|
| 2 | Replace blown fuse or faulty relay feeding the oxygen sensor heater | $10–$60 |
| 3 | Replace the Bank 1 Sensor 1 oxygen sensor if the heater is open or shorted | $50–$250 |
| 4 | Diagnose and repair PCM control circuit faults if power, ground, and sensor test good | $100–$450 |
07 / Related codes
08 / FAQ
What does Bank 1 Sensor 1 mean?
It is the upstream oxygen sensor on the side of the engine with cylinder 1.
Can a bad oxygen sensor heater cause poor gas mileage?
Yes. If the sensor warms up slowly or not at all, fuel control can stay less accurate longer.
Will replacing the oxygen sensor always fix P0031?
No. Wiring, fuse, relay, or PCM control problems can also cause this code.
Can I clear P0031 and keep driving?
You can clear it temporarily, but if the fault remains the check engine light will return and emissions may suffer.
09 / Source and method
- DATA BASIS
- OBD-II REFERENCE + OBD2.HELP
- METHOD
- STATIC VALIDATION
- SAFETY
- INFORMATIONAL
This page combines OBD-II diagnostic reference data with OBD2.help generated diagnostic guidance for code meaning, likely causes, and repair direction.
Publishing uses deterministic schema and build validation, plus manual spot checks on representative pages before release.
Safety-critical diagnosis and repairs should be confirmed with a qualified mechanic, especially when the vehicle is misfiring, overheating, or losing power.