O2 Sensor Delayed Response - Rich to Lean Bank 1 Sensor 1
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.
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.
Real-world scan data
Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.
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?+
Can I just clear P015A?+
Related codes
Read & clear P015A yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.