How to Tell If Your Catalytic Converter Is Failing
Key Takeaway
Is your catalytic converter bad? Here's how to tell for sure without guessing.
Symptoms of a Failing Catalytic Converter
| Symptom | What It Means |
|---|---|
| P0420/P0430 code | Efficiency below threshold |
| Rotten egg (sulfur) smell | Cat is overheating |
| Reduced engine power | Restricted exhaust flow |
| Dark exhaust smoke | Cat can't process exhaust |
| Rattling underneath the car | Internal substrate broken |
| Failed emissions test | Cat isn't cleaning exhaust |
How to Confirm
| Test | What It Shows |
|---|---|
| O2 sensor comparison | Upstream vs downstream waveform similarity |
| Backpressure test | Exhaust pressure > 1.5 PSI = restricted |
| Temperature test | Cat inlet vs outlet temp difference |
| Visual inspection | Substrate damage if removable |
Don't Replace Without Confirming
Up to 40% of catalytic converter replacements are unnecessary. The real cause may be a $150 O2 sensor or upstream issue damaging the cat.
ProHow Steer Helps
Steer analyzes O2 sensor data trends to help you confirm whether it's the cat or the sensor.
Fix Any Engine Issue with Steer
Get instant plain-English explanations for any engine code on your iPhone. Steer stays connected 24/7 to monitor your car's health.
