Emissions

P0159 — O2 Sensor Slow Response (Bank 2 Sensor 2)

Severity: low Safe to drive

What P0159 means

The engine control module monitors the Bank 2 Sensor 2 oxygen sensor, which sits after the catalytic converter and helps judge converter performance. Its voltage should switch quickly and clearly when exhaust oxygen content changes. If the signal changes too slowly, the module sets P0159 and turns on the check engine light.

Symptoms

  • Check engine light on
  • Slightly worse fuel economy
  • Rough idle or hesitation (uncommon)
  • Higher exhaust emissions
  • Emissions test failure

Possible causes

  1. Aged or failing Bank 2 Sensor 2 oxygen sensor
  2. Damaged wiring or corroded connector at the sensor
  3. Exhaust leak near the sensor
  4. Sensor contamination from oil, coolant or additives
  5. Failed sensor heater
  6. Faulty ECM or outdated software (rare)

How to diagnose

  1. Read freeze frame data and check for other codes, especially misfire, catalyst or fuel trim codes.
  2. Inspect the sensor, harness and connector for breaks, chafing, corrosion, soot or oil.
  3. Check the exhaust for leaks upstream of and around the sensor.
  4. Test the sensor heater resistance and power supply per the vehicle's wiring diagram.
  5. Watch live data for Bank 2 Sensor 2: it should respond to throttle changes, not stay lazy or flat.
  6. Review Bank 2 fuel trims to rule out an upstream mixture problem.
  7. Check the signal and ground wires for continuity back to the ECM.
  8. If everything tests fine, look for an ECM software update for your model.

Common fixes

  • Replace the Bank 2 Sensor 2 oxygen sensor
  • Repair the wiring or replace the connector
  • Fix exhaust leaks
  • Correct the source of oil or coolant entering the exhaust
  • Update or replace the ECM (very rare)

Questions and answers

What does P0159 mean?

The downstream oxygen sensor on Bank 2 is reacting to exhaust changes too slowly. It is most often just an aged sensor, but wiring and exhaust leaks should be checked too.

Can I drive with P0159?

Yes, for a while. Don't ignore it for long, though, as emissions can increase and the code may hide other faults.

Do I need a new catalytic converter for P0159?

Usually not. Test and replace the sensor if needed, fix any leaks, and confirm there are no catalyst efficiency codes before considering the converter.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.