Emissions code
P0140: Downstream oxygen sensor shows no activity (bank 1)
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 oxygen sensor behind the catalytic converter on cylinder 1's bank shows no change at all, a flat line. The computer expects it to move at least a little as the exhaust changes. A dead sensor, a broken wire, a blown fuse or a big exhaust leak can all cause it.
- Safe to drive?
- Usually yes, for now
- Most common cause
- Dead O2 sensor
Safe to drive. Emissions only.
What you may notice
- Check-engine light on
- No change in how the car drives
- May fail the emissions readiness check
Common causes, most likely first
- Dead O2 sensor
- Broken wiring or connector
- Blown heater fuse
- Exhaust leak
Check this first
Check the sensor heater fuse and look at the wiring and plug for breaks or corrosion before replacing the sensor. A flat signal from a broken wire looks the same as a dead sensor to the computer.
Other repairs that sometimes fix P0140
| Repair | Typical range, Boston |
|---|---|
| Diagnostic scan (check engine light) | $60 to $290 |
| Catalytic converter replacement | $400 to $1,900 |
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).
P0140 questions
Why flat?
A dead sensor or a broken wire gives no signal, and the computer sees a flat line either way. A quick look at the plug and the wire path can tell the shop which one it is.
Is it the converter?
Not usually. The sensor behind the converter only checks it. A flat signal says the sensor is bad, not that the converter has failed. Replace the sensor first and see if a catalyst code follows.
Will cleaning work?
Rarely. A flat or dead sensor is not just dirty, and spray cleaner does not restore it. The usual fix is replacing the sensor with the right part for your engine and bank.
How much does it cost to fix P0140?
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
- P0136: Downstream oxygen sensor circuit problem (bank 1)
- P0141: Oxygen sensor heater fault (bank 1, after converter)
- P0420: Catalytic converter not working well (bank 1)
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.