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p0420
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Ford · Trucks
Catalyst System Efficiency Below Threshold Bank 1
Quick Answer
Error code P0420 on your Ford Trucks means: Catalyst System Efficiency Below Threshold Bank 1. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
F150F150HF150LF150RF250SDF350SDF-150 King Ranch 2024F-150 Lariat 2024F-150 Limited 2024F-150 Platinum 2024F-150 Tremor 2024F-150 XL 2024F-150 XLT 2024F-250 King Ranch 2024F-250 Lariat 2024F-250 XL 2024F-250 XLT 2024F-350 Lariat 2024F-350 Platinum 2024F-350 XL 2024Maverick Lariat 2024Maverick XL 2024Maverick XLT 2024Ranger Lariat 2024Ranger Raptor 2024Ranger XL 2024Ranger XLT 2024MVKRGR
Likely Causes
  1. Worn or contaminated catalytic converter
  2. Failing downstream O2 sensor on bank 1
  3. Exhaust leak before or after the catalytic converter
  4. Engine misfire causing unburned fuel to damage the catalyst
  5. Use of leaded fuel or excessive oil consumption contaminating the catalyst
How to Fix It
1
Verify no other DTCs are present that could cause catalyst damage
2
Compare upstream and downstream O2 sensor readings on bank 1 with a scan tool
3
Inspect exhaust system for leaks at manifold gaskets and pipe connections
4
Check for engine misfires or oil burning conditions
5
Replace catalytic converter if efficiency test fails
Pro Tip
This issue typically requires professional diagnosis. Attempting this fix without proper training could cause further problems.
Parts You May Need
Catalytic converter (bank 1)
Downstream O2 sensor
Exhaust gaskets
Related Error Codes
P0171P0174P0300P0301P0401
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