OBD codes / P0158
P0158
ModerateO2 Sensor Circuit High Voltage (Bank 2, Sensor 2)
Drivable in the short term — this sensor monitors the catalytic converter rather than running the engine. The one caution: if the signal is high because the engine truly is rich (look for P0175), that condition wastes fuel and can overheat the converter, so get a diagnosis rather than assuming it is just a sensor.
What this code means
This is the opposite flavor of P0157: the post-catalyst oxygen sensor on bank 2 (the engine side without cylinder 1) is reporting a voltage stuck high, as if the exhaust were constantly rich. Because this sensor sits after the catalytic converter, its readings are used mainly to grade the converter, so the code usually arrives with no drivability complaints. A stuck-high signal typically means a failing or contaminated sensor, or a signal wire shorted to voltage — often from insulation chafed through against the sensor's own heater feed. Less often, the engine really is running rich on that bank, in which case P0175 usually shows up too. Sensor contamination from burning coolant or oil is worth keeping in mind on engines with those issues.
Symptoms you might notice
- Check-engine light, usually with no noticeable driving change
- Failed emissions test
- Fuel smell or worse mileage only if the engine is genuinely running rich
- May appear together with P0175 (System Too Rich, Bank 2)
What it costs to fix
Typical range: $100–$450 · about ~0.3–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| O2 sensor (Bank 2, Sensor 2) | $30–$200 | ~0.3–1 hrs |
| Wiring or connector repair | $5–$60 | ~0.5–1.5 hrs |
| Exhaust leak repair (gasket or flange) | $15–$100 | ~0.5–1.5 hrs |
If the sensor is the culprit, this is typically a modest repair. Costs climb when the real cause is elsewhere — a wiring short takes diagnostic time to trace, and if the sensor was contaminated by coolant or oil, the underlying engine issue is the bigger bill.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0158 for my exact vehicle →
Frequently asked
What does high voltage mean on an O2 sensor?
On a conventional oxygen sensor, high voltage corresponds to a rich exhaust — lots of fuel, little oxygen. P0158 means the bank 2 downstream sensor is reporting rich constantly, which is either a true rich condition, a failing sensor, or a wire picking up voltage it should not.
Should I replace the sensor right away for P0158?
Not before two quick checks: whether a rich code like P0175 is also present (fix the mixture first) and whether the harness is chafed or melted where it could short to voltage. If both come up clean, the sensor is the likely fix.
Will P0158 hurt my engine if I wait?
The code itself will not — the downstream sensor has little say in how the engine runs. The risk is indirect: while it is faulty, the computer cannot properly monitor that catalytic converter, and if a real rich condition is behind it, prolonged rich running can damage the converter.
Where is Bank 2, Sensor 2 located?
On the cylinder bank that does not include cylinder 1, screwed into the exhaust after that side's catalytic converter — usually under the vehicle rather than in the engine bay. Which physical side that is varies by engine layout, so check a diagram for your specific model.
Seeing P0158 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0158 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.