Emissions

P015C — Oxygen Sensor Delayed Response, Rich to Lean (Bank 2 Sensor 1)

Severity: medium Safe to drive

What P015C means

The engine control unit watches how quickly the upstream oxygen sensor on Bank 2 changes its signal when the exhaust shifts from rich to lean. A healthy sensor switches almost instantly, and the ECU uses that signal to fine-tune fuel delivery. When the switch is sluggish, the ECU sets P015C and turns on the check engine light.

Symptoms

  • Check engine light on
  • Reduced fuel economy
  • Rough or unstable idle
  • Hesitation when accelerating
  • Reduced engine performance
  • Failed emissions test

Possible causes

  1. Aged or worn Bank 2 Sensor 1 oxygen sensor
  2. Sensor contaminated by soot, oil or coolant
  3. Damaged, corroded or loose wiring or connector
  4. Heater circuit fault in the sensor
  5. Exhaust leak near the sensor
  6. Mixture problem upstream (vacuum leak, injectors, fuel pressure)
  7. Failing catalytic converter (less likely)

How to diagnose

  1. Scan for all codes and review freeze frame data, noting any misfire or fuel trim codes
  2. Confirm which side is Bank 2 (the side without cylinder 1)
  3. Inspect the sensor, harness and connector for chafing, corrosion, oil or soot
  4. Look for exhaust leaks at and ahead of the sensor
  5. Compare short and long term fuel trims between both banks
  6. Watch live sensor data and check that it swings quickly between rich and lean
  7. Test the heater circuit for power and resistance
  8. If wiring and mixture are fine, replace the sensor and clear the code

Common fixes

  • Replace the Bank 2 Sensor 1 oxygen sensor
  • Repair damaged wiring or replace the connector
  • Fix the exhaust leak
  • Correct the underlying mixture problem (vacuum leak, injectors, fuel pressure)
  • Replace the catalytic converter only if diagnosis confirms it is faulty

Questions and answers

What does P015C mean?

The ECU found that the upstream oxygen sensor on Bank 2 is slow to respond when the mixture changes from rich to lean. An aged or dirty sensor is the usual cause, but wiring faults and exhaust leaks can do it too.

Can I drive with P015C?

Generally yes, for a short time. Fuel economy and smoothness will suffer, and running long on a poorly controlled mixture can harm the catalytic converter, so get it checked soon.

Will replacing the sensor fix it?

Often, but not always. Check the wiring, exhaust leaks and fuel trims first, because if one of those is the cause, a new sensor will set the same code again.

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.