Direct Ozone Reduction Catalyst Efficiency Below Threshold
The P2577 code means the vehicle's onboard diagnostic system has detected: Direct Ozone Reduction Catalyst Efficiency Below Threshold. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- hard
- Estimated cost
- $400 - $2,500 (upstream causes first; catalyst or filter replacement at the high end)
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Common Symptoms
- Check Engine Light on
- Usually no drivability symptom at all
- Failed emissions test
- Possible sulfur/rotten-egg smell on catalyst faults
Probable Causes (Ranked by Likelihood)
- The Direct Ozone Reduction Catalyst Efficiency Below Threshold has genuinely degraded and no longer meets its efficiency threshold High
- An upstream fault (misfire, rich/lean running, oil consumption) that damaged it - fix the cause or the replacement fails too High
- Faulty downstream sensor making a good component look bad Moderate
- Exhaust leak upsetting the readings Moderate
Frequently Asked Questions
What does P2577 mean?
P2577 is a generic OBD-II code defined by SAE J2012 as "Direct Ozone Reduction Catalyst Efficiency Below Threshold". It means the control module detected a fault in this circuit
Can I keep driving with P2577?
Yes for normal use, but get it diagnosed - the system is running on a fallback strategy and a small wiring fault left alone tends to become a bigger one.
Does P2577 mean the same thing on every car?
Yes. P2577 is in the generic (SAE J2012) range, so the definition is standardized across manufacturers. The specific component location and repair procedure still vary by vehicle - check your service information.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Fix every other stored code first - efficiency codes are often downstream of a misfire or fuel-trim fault.
-
Compare upstream and downstream sensor activity on a scan tool.
-
Check for exhaust leaks ahead of the sensors.
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Only replace the Direct Ozone Reduction Catalyst Efficiency Below Threshold once upstream causes are excluded - otherwise the new part fails the same way.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- All OBD-II vehicles - this is a generic (SAE J2012) code with the same meaning across makes
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