P0420 on Ford
Catalyst System Efficiency Below Threshold (Bank 1)
P0420 on Ford vehicles indicates catalyst system efficiency below threshold (bank 1). Au7o has documented this code across 4 Ford models — most commonly on EcoSport, Explorer, F-250 Super Duty. P0420 means the engine computer determined the catalytic converter on Bank 1 isn't cleaning the exhaust as efficiently as it should. The computer compares the upstream and downstream oxygen sensors; a healthy converter stores and releases oxygen, so the downstream sensor should read fairly steady, while a worn one lets its readings mirror the upstream sensor. When that efficiency falls below a set threshold, this code is set. While it most often points to a worn-out catalytic converter, it can also be triggered by upstream problems like a faulty oxygen sensor or an exhaust leak, so the converter isn't always the actual fault. Typical repair costs on Ford range from $150 to $2,200, depending on the specific model and root cause.
Common Causes of P0420
- •Worn-out or failing catalytic converter (Bank 1)
- •Faulty or aged downstream (or upstream) oxygen sensor
- •Exhaust leak before or near the oxygen sensors
- •Engine running rich or lean (fuel trim issues)
- •Misfires or oil/coolant contaminating the converter
- •Damaged or aftermarket low-quality catalytic converter
- •Faulty oxygen sensor wiring or connectors
- •Software/calibration needing update (on some vehicles)
P0420 on Ford by Model
Ford EcoSport(1 issue)
- Exhaust Flex Pipe Cracking and Exhaust Leak2018-2022
The Ford EcoSport is known for premature exhaust flex pipe failure, where the flexible coupling between the exhaust manifold and the catalytic converter develops cracks and leaks. The flex pipe deteriorates from thermal cycling and vibration, causing a loud exhaust ticking or hissing noise that is most noticeable at startup and during acceleration. The leak can also trigger oxygen sensor codes and cause the check engine light to illuminate. In areas with road salt, corrosion accelerates the failure.
Ford Explorer(1 issue)
- PTU (Power Transfer Unit) Failure2011-2019
The Power Transfer Unit (PTU) on AWD-equipped Explorers is prone to premature failure due to its proximity to the exhaust pipe and catalytic converter, causing overheating. Fluid leaks from disconnected vent hoses are common, and if fluid level drops too low, the PTU can fail completely, disabling the AWD system.
Ford F-250 Super Duty(1 issue)
- 6.7L Powerstroke Exhaust Manifold Stud Failure2011-2022
The 6.7L Powerstroke diesel engine exhaust manifold studs are prone to breaking due to thermal cycling. The extreme heat cycles of the diesel exhaust cause the studs to fatigue and snap, creating an exhaust leak at the manifold-to-head junction. This produces a ticking noise on cold starts that may diminish when warm, exhaust smell in the cabin, and can trigger check engine lights for exhaust leaks. The driver side manifold is more commonly affected.
Ford Transit Connect(1 issue)
- Catalytic Converter Efficiency Fault (P0420) on 2.5L Duratec2014-2021
Transit Connect models with the 2.5L Duratec commonly generate catalyst efficiency codes, often after repeated misfire events, oil consumption, or exhaust leaks upstream of the catalyst. Owners report a persistent check engine light with no drivability change, or reduced power if the catalyst becomes restricted. NHTSA complaints and owner reports frequently cite P0420 and catalytic converter replacement.
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View P0420 across all makes →Frequently Asked Questions
What does P0420 mean on Ford?▼
P0420 stands for "Catalyst System Efficiency Below Threshold (Bank 1)." P0420 means the engine computer determined the catalytic converter on Bank 1 isn't cleaning the exhaust as efficiently as it should. The computer compares the upstream and downstream oxygen sensors; a healthy converter stores and releases oxygen, so the downstream sensor should read fairly steady, while a worn one lets its readings mirror the upstream sensor. When that efficiency falls below a set threshold, this code is set. While it most often points to a worn-out catalytic converter, it can also be triggered by upstream problems like a faulty oxygen sensor or an exhaust leak, so the converter isn't always the actual fault. On Ford specifically, this code is documented across 4 models.
What causes P0420 on Ford vehicles?▼
Common causes on Ford: Worn-out or failing catalytic converter (Bank 1), Faulty or aged downstream (or upstream) oxygen sensor, Exhaust leak before or near the oxygen sensors, Engine running rich or lean (fuel trim issues), Misfires or oil/coolant contaminating the converter. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0420 on a Ford?▼
Repair costs on Ford range from $150 to $2,200, depending on the specific model and root cause.
Which Ford models have P0420 documented?▼
Au7o has documented P0420 on 4 Ford models: EcoSport, Explorer, F-250 Super Duty, Transit Connect.