P2577
Direct Ozone Reduction Catalyst Efficiency Below Threshold
Emissions (ozone reduction catalyst)
Generic OBD-II
Medium
What it means
P2577 means the direct ozone reduction catalyst — an emissions device on some vehicles that helps break down ground-level ozone — is performing below its required threshold. The engine still runs normally, but the catalyst isn't cleaning the air as designed. Confirm the monitoring sensors are good before replacing the catalyst, since a bad sensor can trigger this code.
Medium
Can I keep driving? Safe to drive short-term — this is an emissions code. The engine runs normally, but the catalyst isn't cleaning the air as designed, so it should be addressed.
Common symptoms
What you'll notice
- Check-engine light on
- No change in how the engine runs in most cases
- Will fail an emissions test
- Possible related emissions monitor codes
Common causes
Most likely first
- Aged or degraded direct ozone reduction catalyst coatingLikely
- Contamination of the catalyst surface (oil, coolant, or fuel additives)Common
- Faulty catalyst temperature or deterioration sensor giving a low readingCommon
- Restricted or damaged airflow across the catalystLess often
- Wiring or connector faults on the monitoring sensorsLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check for temperature-sensor or related emissions codes first.
- Confirm the monitoring sensors and their wiring are good before condemning the catalyst.
- Inspect for contamination sources such as oil or coolant consumption.
- Verify airflow across the catalyst is not blocked or damaged.
- Replace the direct ozone reduction catalyst if efficiency is genuinely below threshold, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P2577?+
Yes for normal driving, but the emissions catalyst is underperforming and the car will fail an emissions test, so plan to repair it.
Can I just clear P2577?+
It comes back once the monitor re-runs and finds low efficiency. Fix the cause rather than clearing it.
Related codes
Often seen with P2577
Read & clear P2577 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