# P0158: O2 Sensor Circuit High Voltage (Bank 2 Sensor 2) **Verdict:** Safe to drive Oxygen sensors - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $100-$400 - **Urgency:** Keep driving - **Most likely:** Failed rear O2 sensor or a shorted wire - **DIY?:** Steps 1-4 ## Quick answer P0158 means the downstream oxygen sensor on bank 2 is reporting a voltage that is too high, as if the exhaust after the catalytic converter were always rich. A sensor that has failed internally or a signal wire shorted to a voltage source are the usual causes, but bank 2 genuinely running rich can also set it. ## What does P0158 mean? The downstream oxygen sensor on bank 2 is mounted after the catalytic converter on the side of a V6 or V8 without cylinder 1. A conventional sensor generates up to about 0.9 volt when the exhaust is short of oxygen and about 0.1 volt when it has plenty. Behind a healthy converter the reading is fairly steady, and the computer uses it to grade the converter and, on many cars, to trim fuel slightly. P0158 sets when the voltage rises above what the sensor can normally produce, often around 1 volt or more, or stays high when the computer expects it to drop, such as when fuel is cut off while coasting. Most cars need the fault on two trips before the light comes on. A reading above the sensor's natural limit almost always means an electrical problem, while a reading that is merely stuck rich can be a real rich mixture. Exact thresholds and test conditions vary by maker. ## What are the symptoms of P0158? - Check engine light on, car usually drives normally - Catalyst monitor incomplete or failed emissions test - Fuel smell or black soot at the tailpipe if bank 2 is running rich - Rich code P0175 at the same time if the mixture is the cause ## What causes P0158? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Failed downstream oxygen sensor** (most common). A rear sensor can fail internally so its output sticks high. One known failure is the heater element shorting to the signal circuit inside the sensor, which pushes the signal well above 1 volt. Age, heat and impact damage from road debris all contribute. If unplugging the sensor drops the reading at the computer, the sensor is the likely fault. 2. **Signal wire shorted to a voltage source** (common). The sensor's signal wire runs beside its heater power wire in the same harness. If melted insulation lets them touch, battery voltage reaches the signal circuit and the reading jumps far above normal. Heat near the exhaust and harnesses pinched during exhaust work are common causes. A shop checks the harness side for voltage with the sensor unplugged. 3. **Real rich condition on bank 2** (less common). A leaking injector, high fuel pressure, a stuck-open purge valve or a misreading sensor can make bank 2 run rich, and the rear sensor correctly reports it. Negative fuel trims, a fuel smell and code P0175 support this. Here the voltage reads high but stays within the normal range, and replacing the sensor will not help. 4. **Sensor contaminated by fuel or oil** (rare). Raw fuel from repeated misfires, or oil from a worn engine, can foul the sensor tip and catalytic converter so the rear sensor reads rich even after the mixture is fixed. This is more likely on engines that have run badly for a long time. Clearing the original problem first, then retesting, shows whether the sensor has recovered. 5. **Engine computer input fault** (rare). Very rarely the sensor input inside the engine computer fails, or water has entered a computer connector and created a path to voltage. Consider this only when the sensor and harness test good, and the high reading persists with the sensor unplugged. Checking for technical bulletins from the maker before replacing a computer is worthwhile. ## How do you diagnose P0158? 1. Read all codes and fuel trims; negative bank 2 trims point to a real rich condition. 2. Watch the bank 2 rear sensor on a scan tool; a reading above about 1.1 volts points to an electrical fault. 3. Coast with your foot off the throttle and see whether the voltage drops during fuel cut. 4. Unplug the sensor and check the harness signal wire for voltage with the key on. 5. Inspect the harness near the exhaust for melted or pinched sections before replacing parts. ## How do you fix P0158, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Replace bank 2 downstream oxygen sensor | $120-$350 | Usually a straightforward job from under the vehicle. | | Repair shorted harness | $100-$300 | Separate and repair the touching wires, then reroute away from heat. | | Fix a rich-running condition on bank 2 | $150-$700 | Depends on the cause, from a purge valve to a leaking injector. | Full price breakdowns: [oxygen sensor replacement cost](/cost/oxygen-sensor-replacement), [fuel injector replacement cost](/cost/fuel-injector-replacement). ## Is it safe to drive with P0158? > **Safe to drive.** Yes, it is usually safe to drive. If the car also smells strongly of fuel, runs rough or shows a rich code, get it checked soon, because running rich for long periods can overheat and damage the catalytic converter. ## Will P0158 fail an emissions test? P0158 keeps the check engine light on, so the car fails an OBD-based emissions test in most states. A rear sensor stuck high also prevents the computer from properly testing the bank 2 converter, leaving the catalyst monitor incomplete. After the repair, the monitors reset and need several days of driving before a retest. ## After the repair: clearing P0158 Clear the code and drive normally, including steady cruising and a few long coasts with your foot off the throttle on a warm engine. On a scan tool, the bank 2 rear sensor should stay below about 0.9 volt and drop toward 0.1 volt when coasting. Once the catalyst and oxygen sensor monitors finish with no pending code, the repair is confirmed. ## How to prevent P0158 - Keep oxygen sensor wiring clipped in its brackets and well away from hot exhaust parts. - Fix misfires quickly so raw fuel does not foul the rear sensor and converter. - Investigate a fuel smell or rich code such as P0175 before it damages the converter. - Choose a sensor built for the downstream position with the correct connector, not a universal splice-in. - Have under-car wiring checked after any collision or debris strike near the exhaust. ## Codes often seen with P0158 - [P0156](/codes/p0156): O2 Sensor Circuit (Bank 2 Sensor 2) - [P0157](/codes/p0157): O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2) - [P0175](/codes/p0175): System Too Rich (Bank 2) - [P0430](/codes/p0430): Catalyst System Efficiency Below Threshold (Bank 2) - [P0172](/codes/p0172): System Too Rich (Bank 1) ## Frequently asked questions ### Can I drive with a P0158 code? Yes, in most cases P0158 is safe to drive with while you arrange a repair. The rear sensor has only a small effect on fueling. If you also notice a fuel smell, black soot, rough running or a rich code, have it checked soon to protect the catalytic converter. ### What does high voltage mean on an oxygen sensor? High voltage means the sensor is reporting rich exhaust, with little oxygen left in it. A normal sensor tops out near 0.9 volt. A reading well above that usually means an electrical short, while a reading pinned near 0.9 volt can mean the engine really is running rich on that bank. ### How much does it cost to fix P0158? Most P0158 repairs cost $100 to $400 at an independent shop. A new downstream oxygen sensor runs about $120 to $350 installed, and repairing a shorted harness about $100 to $300. If bank 2 is truly running rich, the fix could cost $150 to $700 depending on the cause. ### Can a bad oxygen sensor heater cause P0158? Yes, it can. When the heater inside the sensor shorts to the signal circuit, heater voltage leaks onto the signal wire and the reading jumps high. The same can happen in the harness if the two wires melt together. Replacing the sensor or repairing the wiring fixes it. ### Does P0158 mean my catalytic converter is bad? No, P0158 points to the rear sensor, its wiring or a rich mixture, not the converter. While the sensor reads wrong, the computer cannot test the converter properly. After the fix, a weak converter would show up as P0430, and only then should replacement be considered. ### Can I fix P0158 myself? Often yes. Replacing an accessible rear oxygen sensor needs an oxygen sensor socket, penetrating oil and a safe way to raise the car. Checking for shorts needs a multimeter and a wiring diagram. If the problem turns out to be a rich mixture on bank 2, a shop diagnosis is usually worth it. ### What is the difference between P0138 and P0158? Both mean a downstream oxygen sensor voltage is too high. P0138 is the rear sensor on bank 1, the side with cylinder 1, and P0158 is the rear sensor on bank 2. Both codes together suggest a shared cause, such as a rich fueling problem affecting both banks. ### Will P0158 pass an emissions test? No, the check engine light alone fails an OBD-based emissions test in most states. The bank 2 catalyst monitor may also be incomplete. After the repair, drive several days with a mix of steady cruising and coasting so the monitors complete, then confirm they read ready before testing. ### Can a leaking fuel injector cause P0158? Yes, if the leaking injector is on bank 2. Extra fuel makes that bank run rich, and the rear sensor reads high as a result. Clues include hard hot starts, a fuel smell and negative fuel trims for bank 2. A shop can test fuel pressure hold and injector balance. ### Why does my scan tool show over 1 volt on the rear sensor? A reading over about 1 volt usually means voltage is getting onto the signal wire from somewhere else. The most common sources are a sensor whose heater has shorted internally or harness wires melted together. A conventional oxygen sensor cannot generate that much voltage on its own. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other oxygen sensors codes - [P0140 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)](https://diagxcar.com/codes/p0140) - [P0141 O2 Sensor Heater Circuit (Bank 1 Sensor 2)](https://diagxcar.com/codes/p0141) - [P0151 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0151) - [P0153 O2 Sensor Circuit Slow Response (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0153) - [P0155 O2 Sensor Heater Circuit (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0155) - [P0156 O2 Sensor Circuit (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0156) - [P0157 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0157) - [P0161 O2 Sensor Heater Circuit (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0161) - [P0171 System Too Lean (Bank 1)](https://diagxcar.com/codes/p0171) - [P0172 System Too Rich (Bank 1)](https://diagxcar.com/codes/p0172) ## Symptoms - [Why does my car smell like gas?](https://diagxcar.com/symptoms/car-smells-like-gas) - [Why is black smoke coming from my exhaust?](https://diagxcar.com/symptoms/black-smoke-from-exhaust) ## Repair costs - [Oxygen sensor replacement cost](https://diagxcar.com/cost/oxygen-sensor-replacement): $150-$450 - [Fuel injector replacement cost](https://diagxcar.com/cost/fuel-injector-replacement): $300-$1,500 --- Source page: https://diagxcar.com/codes/p0158 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.