P0159 - O2 Sensor Circuit Slow Response (Bank 2, Sensor 2)

Bank 2 downstream oxygen sensor is switching too slowly.

Treat the code as the starting point: compare symptoms, likely causes, and repair paths before pricing parts or moving into an estimate.

Code Overview

Bank 2 downstream oxygen sensor is switching too slowly.

Common Causes

• Aging downstream oxygen sensor on bank 2 sensor 2
• Exhaust leak affecting downstream sensor readings
• Catalyst efficiency problem on bank 2
• Rich or lean running condition affecting the monitor

Symptoms

• Check-engine light with little or no drivability change
• Failed emissions readiness or inspection
• Catalyst monitor may not complete normally

Diagnostic Steps

1. Watch bank 2 sensor 2 response on a scan tool after the engine is fully warm
2. Check for exhaust leaks ahead of the downstream sensor
3. Look for companion fuel-trim, misfire, or catalyst codes first
4. Compare downstream sensor behavior to catalyst and fueling conditions before replacing parts

Repair Difficulty

Moderate

General difficulty estimate for the most common repair path.

Likely Repairs & Cost Guides

Use symptoms, scan data, and quick checks to confirm the likely repair path before pricing parts. The estimator helps compare repair paths before replacing anything unnecessarily.

Related OBD Codes

Browse nearby code-family pages when the same fault pattern overlaps across systems, such as misfire, lean fuel trim, EVAP sealing, cooling, or charging faults.

Next Steps

Move from code lookup to diagnosis, then estimate the likely repair only after symptoms, causes, and checks point to the same path.