Faulty or aged downstream oxygen sensor on Bank 2; Signal wire shorted to voltage, or damaged or chafed wiring near the exhaust; Corroded, contaminated or loose connector at the sensor; Genuinely rich running on Bank 2, such as a leaking injector or high fuel pressure; Contaminated sensor from coolant, oil or silicone entering the exhaust; Fault in the engine control unit sensor input circuit.

P0158

O2 Sensor Circuit High Voltage Bank 2 Sensor 2.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
58: FaultThe specific fault in that area

What it means

P0158 means the engine control unit has seen a persistently high voltage from the oxygen sensor on Bank 2, Sensor 2, which is the downstream sensor after the catalytic converter on the side of the engine opposite Bank 1. The signal has stayed above the expected range, typically near or above about 1 volt, for longer than the control unit allows. This points to a sensor, wiring or exhaust condition fault, or in some cases a genuinely rich mixture.

Symptoms

Malfunction indicator lamp on
Usually no noticeable change in driving
Possible rich running, poor fuel economy or a fuel smell if a rich condition is the root cause
Possible failed emissions test
Other fuel trim or misfire codes stored alongside

Possible causes

Faulty or aged downstream oxygen sensor on Bank 2likely
Signal wire shorted to voltage, or damaged or chafed wiring near the exhaustlikely
Corroded, contaminated or loose connector at the sensorpossible
Genuinely rich running on Bank 2, such as a leaking injector or high fuel pressurepossible
Contaminated sensor from coolant, oil or silicone entering the exhaustpossible
Fault in the engine control unit sensor input circuitrare

How to diagnose

Read all stored and pending codes and note any fuel trim, misfire or other oxygen sensor codes, then review the freeze frame data.
Confirm which sensor is Bank 2 Sensor 2 for this engine, as layout depends on the model.
Inspect the sensor wiring and connector for heat damage, chafing, corrosion, water ingress and push-out pins.
With the engine warm, watch live data for the Bank 2 downstream sensor and see whether it sits high and fixed or reacts to changes in throttle.
Check short and long term fuel trims on Bank 2 against Bank 1 to see whether the engine is really running rich.
Unplug the sensor and check the signal and reference circuits for a short to voltage, and the ground circuit for continuity, using the manufacturer wiring diagram.
Check the heater circuit supply and resistance of the sensor against the specification for the model.
If the mixture is rich, test fuel pressure and injector operation and look for signs of coolant or oil contamination.

How to fix

Replace the Bank 2 downstream oxygen sensor if it is faulty or contaminated.
Repair or replace damaged wiring, and clean or renew the connector terminals.
Correct the cause of any rich running, such as a leaking injector or fuel pressure fault.
Fix any coolant or oil leak into the combustion chamber that has contaminated the sensor or catalytic converter.
Repair or replace the engine control unit only after confirming the sensor, wiring and mixture are all correct.

Can I keep driving?

Low severity

The car can normally be driven while you book it in, as the downstream sensor mainly monitors catalytic converter efficiency. If the engine is running rich, have it checked soon to avoid fuel waste and catalytic converter damage.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.