P0158 — Oxygen sensor circuit high voltage — bank 2, sensor 2

P0158 indicates signal voltage above the monitor limit for bank 2, sensor 2. Sensor 2 is usually after the first catalyst; some exhaust layouts also have sensor 3. This alone does not prove a rich mixture: a short circuit can influence the signal.

Affected system: Powertrain

Symptoms

• Engine warning lamp and a stored code.
• Driveability symptoms are often absent; emissions inspection issues may occur.

Possible causes

• Signal shorted to supply or the heater circuit.
• Damaged or contaminated sensor; an actual rich mixture requires separate confirmation.

What to check

• Confirm B2S2 in the engine diagram and save related codes and freeze-frame data before clearing anything.
• With the exhaust cold, inspect the B2S2 harness for melted insulation, rubbing, water in the connector and loose terminals.
• Compare the B2S2 signal with the OEM limit; check isolation from heater supply before attributing the reading to the mixture.
• Use the OEM procedure to separate sensor and harness faults; compare the signal with fuel trims and the other sensors.
• After correcting the confirmed fault, repeat the OEM monitor conditions and check for code recurrence, beyond merely extinguishing the lamp.

Also written as: P0158-00, P015800, PO158 (some scan tools add the fault-type byte, e.g. -00).