P0158
O2 Sensor Circuit High Voltage (Bank 2, Sensor 2)
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P0158 indicates that the downstream oxygen sensor on Bank 2 is reporting a voltage higher than the expected range for an extended period. While the sensor normally oscillates between 0.1V and 0.9V, this code sets when the voltage remains above the upper threshold (typically above 0.9V) for too long, suggesting the sensor is reading a rich exhaust condition.
A high voltage reading from the downstream sensor can mean either the sensor itself has failed or there is a genuine rich fuel condition on Bank 2. If the engine is truly running rich, you may notice black smoke from the exhaust, a fuel smell, and decreased fuel economy. If it is just a sensor failure, driveability symptoms are usually minimal since this sensor primarily monitors catalytic converter efficiency.
Start diagnosis by checking for related codes — if you also see P0172 or P0175 (system too rich), the problem is likely a genuine rich condition that needs to be addressed in the fuel system. If P0158 appears alone, the sensor or its wiring is the most likely culprit. Replacing the downstream O2 sensor is a relatively simple DIY job requiring a specialized O2 sensor socket and is accessible from underneath most vehicles.
Severity
Symptoms
- •Check Engine Light is on
- •Reduced fuel economy
- •Black smoke from the exhaust in some cases
- •Engine may run rich
- •Noticeable fuel smell from the tailpipe
- •Rough idle or hesitation
Likely Causes
The Bank 2 post-catalytic converter oxygen sensor has failed internally and is producing a constantly high voltage signal, indicating an overly rich exhaust reading.
The O2 sensor signal wire has a short to a power source, artificially driving the voltage reading higher than what the sensor is actually measuring.
A genuine rich running condition on Bank 2 caused by leaking fuel injectors, high fuel pressure, or a faulty fuel pressure regulator is producing legitimately high O2 sensor voltage.
The sensor element has been contaminated by silicone (from certain RTV sealants), coolant (from a head gasket leak), or excessive oil consumption, causing it to read high.
In rare cases, the PCM is providing an incorrect reference voltage to the sensor circuit, resulting in a high voltage reading.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace the Bank 2 Sensor 2 oxygen sensor
- Repair shorted wiring in the O2 sensor circuit
- Diagnose and repair rich running condition (fuel injectors, fuel pressure regulator)
- Replace contaminated O2 sensor and address root cause of contamination
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