P0158 code: O2 Sensor Circuit High Voltage (Bank 2, Sensor 2)
P0158 means o2 Sensor Circuit High Voltage (Bank 2, Sensor 2). The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0158 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.
P0158 symptoms
- 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 P0158
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 →
How to fix P0158
Easy — basic tools, most owners can do this
- Rule out a real rich condition on bank 2
Check for P0175 and compare long-term fuel trims: bank 2 strongly negative with bank 1 near normal suggests an injector leaking on that bank, while both banks negative points at fuel pressure or the purge system. Sort out a genuine rich mixture first — it threatens the converter far more than a faulty monitor sensor does.
- Coast with the throttle closed and watch it drop
During a long closed-throttle coast from speed, the engine computer cuts fuel and the exhaust turns to almost pure air. Any working downstream sensor should plunge toward the bottom of its range within a few seconds; if bank 2 sensor 2 stays high through a fuel cut, the reading isn't coming from the exhaust at all.
- Ohm the sensor for an internal heater-to-signal short
Unplug the sensor and, on a typical four-wire unit, measure resistance between each heater pin and each signal pin on the sensor side. Those circuits should be fully isolated; any continuity means heater voltage is leaking into the signal inside the sensor body, and replacement is the fix.
- Check the harness for a short to power
With the sensor still unplugged and the key on, measure the harness-side signal terminal. More than a small bias voltage there means the wire is touching a power source — often its own heater feed where the loom has melted on the pipe or rubbed through along the transmission tunnel.
- Fit a new sensor and look for what fouled the old one
With the wiring proven, install the replacement and inspect the old tip: heavy dark deposits or a crusty coating suggest oil or coolant consumption reaching the bank 2 exhaust, which will shorten the new sensor's life unless it's tracked down. A steady mid-range reading after a warm drive confirms the repair.
DIY or shop? The checks here are cheap and decisive: a coast-down test on the road, a few resistance readings, and one voltage reading at the connector separate a shorted sensor from a damaged harness or a rich engine. The sensor swap from underneath is routine with jack stands. Take it to a shop if the evidence points to a genuinely rich bank — injector testing and fuel-pressure work need more equipment — or if the short is somewhere in the harness you can't see without removing heat shields or the exhaust.
Tools for the DIY steps: Scan tool with live data · Digital multimeter · Wiring diagram for your vehicle · O2 sensor socket · Jack stands · Penetrating oil
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0158.
Start a case with P0158 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0158?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0158: common questions
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.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0158 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0158 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.