P0159 O2 Sensor Circuit Slow Response Bank 2 Sensor 2

P0159 indicates slow oxygen sensor response on bank 2 sensor 2. The downstream bank 2 sensor changes slower than the monitor expects.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the catalyst before confirming downstream sensor heater operation, wiring, and exhaust integrity.

Symptoms of P0159

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0159

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Compare bank 2 sensor 2 response during fuel changes, deceleration fuel cut, catalyst monitor activity, and heater operation.
Inspect exhaust leaks, heater function, wiring near exhaust heat, connector condition, catalyst condition, and bank 2 fuel trim issues.
Check whether the slow response appears only cold, hot, at cruise, after exhaust service, or with rich or lean operation.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.