What Does P0158 Mean?
The downstream O2 sensor on Bank 2 (Sensor 2, post-catalytic converter) is reporting a persistently high voltage, indicating a rich exhaust reading. The voltage remains above the expected maximum threshold for longer than the PCM allows. This could be caused by a sensor fault, a wiring short to voltage, or an actual rich exhaust condition reaching the downstream sensor due to catalytic converter issues. The driver may not notice symptoms unless the catalyst is severely degraded.
Common Causes
35%
Failed downstream O2 sensor stuck producing high voltage
20%
O2 sensor signal wire shorted to the heater power wire or battery voltage
20%
Catalytic converter saturated or failing, allowing rich exhaust gases to pass through
15%
Persistent rich condition on Bank 2 overwhelming the catalytic converter
10%
Water intrusion or contamination in the sensor connector causing false readings
Diagnostic Steps
1
Monitor Bank 2 Sensor 2 voltage — a stuck reading above 0.8V suggests the sensor is shorted high or detecting a real rich condition; check if Bank 2 Sensor 1 is also reading rich.
2
Disconnect the sensor connector and check if voltage drops to approximately 0.45V (bias voltage) — if it remains high, the signal wire is shorted to voltage in the harness.
3
Check Bank 2 fuel trims — if the upstream sensor and fuel trims indicate normal operation, the downstream sensor or its wiring is at fault.
4
Inspect the sensor connector for water intrusion, melted insulation, or wires touching each other — the signal wire may be making contact with the 12V heater supply.
5
If a real rich condition is confirmed upstream, check for leaking fuel injectors, high fuel pressure, and stuck-open EVAP purge valve on Bank 2.
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
The downstream O2 sensor on Bank 2 (Sensor 2, post-catalytic converter) is reporting a persistently high voltage, indicating a rich exhaust reading. The voltage remains above the expected maximum threshold for longer than the PCM allows. This could be caused by a sensor fault, a wiring short to volt...
The most common cause of P0158 (Oxygen Sensor High Voltage, Engine Bank B, Downstream of Catalytic Converter) is: Failed downstream O2 sensor stuck producing high voltage
Typical repair costs for P0158 range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving in most cases. If the high reading is due to a failed catalytic converter allowing rich exhaust through, there is a small risk of elevated undercarriage temperatures. The MIL will be on and the vehicle will fail emissions testing.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0158 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions / Exhaust System
Difficulty
Type
Generic (SAE)
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