Emissions code
P0157: Rear oxygen sensor reads low (bank 2, after 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 oxygen sensor behind the catalytic converter on the side without cylinder 1 is reading low voltage. It might be worn, shorted to ground or reading outside air from an exhaust leak near it. This sensor mainly watches how well the converter does its job.
- Safe to drive?
- Usually yes, for now
- Most common cause
- Aging rear sensor
Safe to drive.
What you may notice
- Check-engine light on
- No change in how the car drives
- May appear with a converter code
Common causes, most likely first
- Aging rear sensor
- Exhaust leak
- Wiring short
- Plug corrosion
- Engine running lean on that side
Check this first
Look for the matching sensor on the other bank, and ask the shop to compare readings. If both rear sensors act the same, the cause is likely shared. If only this one is off, a local leak or sensor problem is more likely.
Other repairs that sometimes fix P0157
| 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).
P0157 questions
Which sensor is this?
It is the sensor after the catalytic converter on the engine side that does not hold cylinder 1. On a V-type engine, that is the opposite bank from bank 1.
Is the converter bad?
Usually not, but if a catalyst code like P0430 shows up as well, then the converter deserves a look. Do not replace a converter only based on this code.
Can I swap sensors from side to side?
Shops sometimes do this as a test, because if the code moves to the other bank, the sensor is bad. It is not always allowed with every design, so let the shop decide whether to try it.
How much does it cost to fix P0157?
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
- P0137: Rear oxygen sensor reads low (bank 1, after converter)
- P0430: Catalytic converter not working well (bank 2)
- P0161: Oxygen sensor heater fault (bank 2, after converter)
- P0175: Engine getting too much fuel (bank 2)
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.