DTC P0420 — Catalyst System Efficiency Below Threshold (Bank 1)
P0420 indicates: Catalyst System Efficiency Below Threshold (Bank 1).
Diagnostic summary
P0420
What it means
Catalyst System Efficiency Below Threshold (Bank 1)
Can you drive?
⚠️ Drive with caution
Urgency
Medium 5/10
Typical price
$150 – $1,200
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Updated May 7, 2026 Seen on Powertrain
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ℹ️ What does it mean?
Catalyst System Efficiency Below Threshold (Bank 1)
🔍 Symptoms
- • Check Engine Light on
- • Reduced engine performance
- • Increased fuel consumption
- • Unusual engine behavior
⚠️ Possible Causes
- ⚠ Worn catalytic converter
- ⚠ Faulty downstream O2 sensor
- ⚠ Exhaust leak
- ⚠ Engine misfire
- ⚠ Bad fuel
🚗 Can I drive with this code?
Drive with caution
Drive with caution. Schedule a repair soon.
🔧 How to Diagnose
- 1 Read DTCs with OBD-II scanner
- 2 Check freeze frame data
- 3 Inspect related components
- 4 Clear codes and test drive
🛠️ How to Fix
- 1 Replace catalytic converter
- 2 Replace downstream O2 sensor
- 3 Fix exhaust leak
- 4 Fix misfire
💰 Estimated Repair Cost
Repair cost by car / region
Early rough estimate. Accuracy improves as more real repair stories are added.
DIY / parts$53 – $780
Mechanic / labor$68 – $900
Repair range$150 – $1,200
❓ FAQ
What does P0420 mean?
Catalyst System Efficiency Below Threshold (Bank 1)
How serious is P0420?
Severity: medium. Drive with caution. Schedule a repair soon.
How much does it cost to fix P0420?
Estimated repair cost: $150–$1200 depending on vehicle and region.
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