P0420: Catalyst System Efficiency Below Threshold
Can you still drive? Yes, but get it checked soon. Prolonged driving may damage the catalytic converter further.
What Does P0420 Mean?
Code P0420 indicates that the catalytic converter is not operating at peak efficiency. The downstream oxygen sensor detects that the converter is not reducing exhaust emissions as effectively as expected. This is one of the most common OBD-II codes.
Need to read your codes?
An OBD-II scanner lets you read and clear diagnostic trouble codes from your vehicle's computer. Most scanners work with any car made after 1996.
Browse OBD-II Scanners on AmazonCommon Causes
- Worn catalytic converter
- Faulty oxygen sensor
- Exhaust leak
- Engine misfire damaging converter
Symptoms
- Check engine light on
- Reduced fuel efficiency
- Slight sulfur smell from exhaust
Diagnostic Steps
- 1Read and document the freeze frame data
- 2Check for exhaust leaks
- 3Test upstream and downstream O2 sensors
- 4Inspect catalytic converter for damage
- 5Check for engine misfires
Recommended Parts & Tools
catalytic converter
oxygen sensor
Estimated Repair Cost
| Type | Estimated Cost |
|---|---|
| Total Repair Cost Range | $200 - $2500 |
Get a Personalized AI Diagnostic Report
Get a detailed AI diagnosis for code P0420 specific to your vehicle. Includes step-by-step repair instructions, exact parts needed, and a cost breakdown tailored to your make and model.
Chat with AI About P0420Commonly Affected Vehicles
Related Recalls
Frequently Asked Questions
Is P0420 serious?
P0420 is moderate severity. Your vehicle is safe to drive short-term, but the catalytic converter may need replacement.
Can I pass emissions with P0420?
No, P0420 will cause an emissions test failure in most states.
Community Fix Reports
Community reports are user-submitted and not verified by Auto AI Buddy. Results may vary.
Related Codes
Affiliate Disclosure: This page contains affiliate links. If you purchase products through these links, we may earn a small commission at no additional cost to you. This helps us maintain this free resource. We only recommend products we believe will help you diagnose and repair your vehicle. Prices shown are estimates and may vary.