P015C
O2 Sensor Delayed Response - Rich to Lean Bank 2 Sensor 1
Emissions / oxygen sensor
Generic OBD-II
Medium
What it means
P015C means the upstream oxygen sensor on bank 2, sensor 1 is slow to react when the mixture changes from rich to lean. The delayed signal makes the ECM's fuel control less accurate, which can slightly worsen idle quality, fuel economy, and emissions. It's typically caused by an aged or contaminated sensor, an exhaust or intake leak, or a fueling issue — it does not cause a no-start.
Medium
Can I keep driving? Safe to drive — the engine runs, but a delayed upstream oxygen sensor can reduce fuel economy and raise emissions; repair it before an emissions test.
Common symptoms
What you'll notice
- Check-engine light on
- Slightly rough idle or engine surge
- Reduced fuel economy
- Increased emissions
Common causes
Most likely first
- Aged or contaminated bank 2 sensor 1 (upstream) oxygen sensorLikely
- Exhaust leak near the sensor pulling in outside airCommon
- Unmetered intake air leak affecting the mixtureCommon
- Fuel-pressure or injector issues altering the air/fuel ratioLess often
- Corroded connector or wiring fault at the sensorLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and watch the bank 2 sensor 1 signal transition rich-to-lean — a lagging response confirms the code.
- Inspect the sensor connector and wiring for corrosion or damage.
- Check for exhaust leaks between the manifold and the sensor, and for intake (vacuum) leaks.
- Verify fuel pressure and injector operation are within spec.
- Replace the aged upstream oxygen sensor if it stays delayed after leaks are ruled out. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P015C?+
Yes, short-term. The car runs, but a sluggish oxygen sensor hurts fuel economy and emissions. Have it repaired before an emissions test or long trip.
Can I just clear P015C?+
It comes back within a few drive cycles if the sensor is worn or there's a leak. Fix the underlying cause instead of only clearing it.
Related codes
Often seen with P015C
Read & clear P015C yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX