Emissions code
P0031: Oxygen sensor heater circuit low (bank 1, before converter)
How this range is built
| Part of the job | Low | High |
|---|---|---|
| Parts | $40 | $180 |
| Labor: 0.6 to 1 hours × $125 to $175 an hour | $75 | $175 |
| Fees: shop supplies, disposal, diagnostics | $0 | $15 |
| Total, rounded | $110 | $370 |
The hourly rate is the BLS Occupational Employment and Wage Statistics, May 2025 average pay for this trade in Boston, $31.54 an hour, times 4 to 5.5 to cover what a shop bills (overhead, tools, insurance, profit). Parts are a band from budget aftermarket to the manufacturer part. Full method.
Not a repair shop, estimates only. Typical range, estimate. Not a quote. Your car, parts and shop change the number.
This is the range for the most common fix, oxygen sensor replacement (one sensor). Which repair your car needs depends on a proper diagnosis.
The heater inside the front oxygen sensor draws less current than the computer expects, which looks like a short to ground or a wire that is open. With the heater off, the sensor takes much longer to start working, which affects how clean the engine runs right after a cold start.
- Safe to drive?
- Usually yes, for now
- Most common cause
- Failed sensor heater
Safe to drive; the light will stay on.
What you may notice
- Check-engine light on
- Slightly worse fuel economy
- Rough idle for the first minute
Common causes, most likely first
- Failed sensor heater
- Wiring shorted to ground
- Corroded plug
- Blown fuse
- Computer driver fault
Check this first
Look at the sensor plug and the wire along the exhaust for burn marks, rubbing or pinched insulation. A wire that touches hot metal can short to ground and cause exactly this code without the sensor being bad.
Other repairs that sometimes fix P0031
| Repair | Typical range, Boston |
|---|---|
| Diagnostic scan (check engine light) | $60 to $290 |
| Vacuum leak repair | $100 to $530 |
Before you pay
- Ask the shop what test showed this part is the cause, not just that the code appeared.
- Ask for parts and labor listed separately, and for the hours.
- Ask for a written OK before any extra work. Massachusetts rules require written authorization before repairs.
Got a quote already? Check it against the range. Want to see if your car has a recall tied to this problem? Check recalls by VIN.
Need to read a code yourself? OBD-II scanners on eBay (affiliate link, disclosure).
P0031 questions
What does low circuit mean?
Low means the circuit pulls less current than expected, usually because the wire is broken or has shorted to ground. It describes the electrical reading, not the sensor itself.
Is the wiring or sensor more likely?
Sensors fail more often than wires, but looking over the wiring costs almost nothing. A shop can also measure heater resistance to confirm, which avoids replacing a good sensor.
Will the car run poorly?
Not in a way you can feel. The first few minutes after a cold start may be a little less efficient, and the engine may idle rougher than usual, but it will drive normally afterward.
How much does it cost to fix P0031?
The most common fix, oxygen sensor replacement (one sensor), has a typical range of $110 to $370 in Boston. It is an estimate built from parts prices and local labor wages, not a quote. Your car and shop change it.
Related codes
- P0030: Oxygen sensor heater circuit fault (bank 1, before converter)
- P0135: Oxygen sensor heater fault (bank 1, before converter)
- P0037: Oxygen sensor heater circuit low (bank 1, after converter)
- P0131: Oxygen sensor reads low voltage (bank 1, before converter)
More emissions codes
Code meaning written in our own words. Some codes mean different things on different makes, so check your scan tool or manual. Not a repair shop, estimates only.