P015A
O2 Sensor Delayed Response - Rich to Lean Bank 1 Sensor 1
Oxygen sensor / emissions
Generic OBD-II
Medium
What it means
P015A means the upstream oxygen sensor on Bank 1 (Sensor 1, before the catalytic converter) is slow to swing from a rich to a lean reading. Since this sensor drives fuel-trim corrections, a delayed response can hurt economy and cause a mild rough idle or hesitation, though the car generally still drives. It most often points to an aging sensor.
Medium
Can I keep driving? Yes — a slow-responding upstream sensor lets the car run but hurts fuel trim and economy; get it fixed to restore proper mixture control.
Common symptoms
What you'll notice
- Check-engine light on
- Increased fuel consumption
- Possible rough idle, hesitation, or surge
- May fail an emissions test
Common causes
Most likely first
- Aging or contaminated upstream oxygen sensor (Bank 1, Sensor 1)Likely
- Corroded connector or damaged wiring at the sensorCommon
- Exhaust leak drawing in air near the sensorCommon
- Incorrect fuel pressure or dirty/leaking injectorsLess often
- Intake (vacuum) air leakLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and graph the upstream sensor's response on a scan tool.
- Inspect the sensor wiring and connector and check for exhaust and vacuum leaks.
- Verify fuel pressure and injector condition.
- Replace the upstream O2 sensor if it responds slowly.
- Clear and retest over a full drive cycle.
FAQ
Quick answers
Is it safe to drive with P015A?+
Yes. The car runs, but the slow upstream sensor degrades fuel trim, so you may see worse economy or a mild rough idle. Repair it to restore proper mixture control.
Can I just clear P015A?+
It returns once the sensor's response is re-tested. A genuinely slow sensor needs replacing, or the mixture/exhaust issue behind it corrected.
Related codes
Often seen with P015A
Read & clear P015A 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