P0420
Catalyst System Efficiency Below Threshold
Description
Catalyst System Efficiency Below Threshold (Bank 1) This body system diagnostic trouble code indicates an issue with the vehicle's comfort, safety, or convenience systems.
OBD Codes Details
Possible Causes
Blown fuse, faulty switch, damaged wiring harness, poor electrical connection
Solution
Check fuses and relays, inspect wiring harness, test switches and sensors, repair damaged circuits
Symptoms
- Reduced fuel efficiency
- Strong exhaust odor
- Engine may run slightly rougher
- Check engine light is on
- Failed emissions test
Diagnostic Recommendations
- Test catalytic converter efficiency using OBD data
- Check oxygen sensors upstream and downstream of catalyst
- Inspect exhaust system for leaks before the catalyst
- Test engine compression and fuel trim values
- Check for oil burning or excessive fuel consumption
- Verify proper engine operation without other codes present
Repair Cost Estimate
- Oxygen sensor replacement: $200-500
- Catalytic converter replacement: $800-2500
- Exhaust system repair: $200-600
- Engine tune-up: $200-500
- Total diagnostic and repair: $500-4000
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Fact-checking completed
Verified by:
Pavel Volkov
Created:
Last updated:
Information verified against official sources
Official Sources
Society of Automotive Engineers
Official OBD-II diagnostic trouble codes standard (SAE J2012)
Automotive engineering standards organization
International Organization for Standardization
International standard for vehicle diagnostic systems
International standards for automotive diagnostics
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