Can You Drive With Code P0420?
Drive with caution (short trips only)Caution: You can usually drive with code P0420 for a short time if the car feels normal, but you should schedule diagnostics soon and avoid long trips until it's fixed.
How far can you drive?
Typically 1,000–3,000 miles or more if no other symptoms are present and the car drives normally. P0420 reflects a below-threshold efficiency reading, not a catastrophic failure—but the underlying cause needs to be diagnosed.
Stop driving immediately if you notice these signs
- Check engine light starts flashing alongside P0420
- Engine develops a rough idle or misfire
- Significant, sudden drop in fuel economy
- Strong rotten-egg or sulfur smell from the exhaust
- Noticeable loss of power under acceleration
What happens if you ignore it?
The catalytic converter will continue degrading and eventually require full replacement ($400–$2,400). If the code is caused by an active misfire or a rich-running condition, continued driving accelerates catalyst damage and makes the repair more expensive.
Typical repair cost: $400–$2400
When to call a tow instead of driving
- Check engine light starts flashing alongside P0420
- Engine develops a noticeable misfire or rough running
- Significant power loss or fuel economy drop
Frequently asked questions
Will P0420 go away on its own?
Unlikely. P0420 means the catalytic converter is operating below the efficiency threshold the ECM expects. The catalyst doesn't recover on its own. Occasionally an upstream O2 sensor replacement resolves it if the sensor—not the catalyst—was the culprit.
Is P0420 serious?
Not immediately dangerous to drive, but it will fail an emissions test and indicates your catalytic converter is deteriorating. Addressing the root cause sooner avoids a more expensive full converter replacement down the road.
Can I clear P0420 to pass an emissions test?
Clearing the code resets the OBD readiness monitors, which means you will fail the emissions inspection until the monitors complete their drive cycle (typically 50–100 miles of mixed driving). Don't clear codes right before a test.