Emissions code
P0158: Downstream oxygen sensor reads high voltage (bank 2)
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 keeps reading a very high voltage, as if the exhaust is rich. It may be telling the truth because of a rich engine, or the sensor or its wiring may be at fault and giving a false high reading.
- Safe to drive?
- Usually yes, for now
- Most common cause
- Failed O2 sensor
Safe to drive. Emissions only.
What you may notice
- Check-engine light on
- Possible fuel smell
- Slightly worse fuel economy
Common causes, most likely first
- Failed O2 sensor
- Wiring shorted to voltage
- Real rich mixture
- Converter issue
Check this first
Have the shop check fuel trims on bank 2. If the computer is pulling a lot of fuel out, the engine really is rich and the cause is upstream. If the trims are normal, the sensor or its wiring is the problem.
Other repairs that sometimes fix P0158
| Repair | Typical range, Boston |
|---|---|
| Diagnostic scan (check engine light) | $60 to $290 |
| Fuel injector replacement (one injector) | $180 to $910 |
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).
P0158 questions
Does a rich mixture matter?
Over time, yes. A rich mix wastes fuel and the extra unburned fuel can overheat and damage the catalytic converter. That makes it worth fixing within weeks rather than months.
Bank 2?
Bank 2 is the side of the engine that does not hold cylinder 1. On a V-type engine, that is the opposite bank, and a shop can show which side that is on your car.
Fix urgent?
It is not an emergency, but do not ignore it. The car runs, but the extra fuel and the failed readiness check can add up, and a repair is easier than a new catalytic converter.
How much does it cost to fix P0158?
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
- P0157: Rear oxygen sensor reads low (bank 2, after converter)
- P0172: Engine getting too much fuel (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.