P0420 on Dodge
Catalyst System Efficiency Below Threshold (Bank 1)
P0420 on Dodge vehicles indicates catalyst system efficiency below threshold (bank 1). Au7o has documented this code across 5 Dodge models — most commonly on Challenger, Dakota, Dart. 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 Dodge range from $200 to $8,500, 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 Dodge by Model
Dodge Challenger(1 issue)
- HEMI Exhaust Manifold Bolt Failure2008-2023
Exhaust manifold bolts break due to thermal cycling causing the bolts to become brittle and snap, especially on the passenger side. Dissimilar metals (iron manifold, aluminum head) accelerate the process. Creates a ticking noise at cold startup. Common across all HEMI-powered LX/LC platform vehicles.
Dodge Dakota(1 issue)
- Plenum Gasket Failure (5.2L/5.9L Magnum V8)1997-2003
The plenum gasket between intake manifold and engine block fails, allowing oil into combustion chambers. Same issue as 1st-gen Durango. Causes oil consumption, pinging, and rough idle.
Dodge Dart(1 issue)
- 2.4L MultiAir Excessive Oil Consumption2013-2016
The 2.4L Tigershark MultiAir II engine has defective piston rings allowing oil into combustion chamber. Owners report 1 quart per 1,000-2,000 miles. FCA considered up to 1 quart per 2,000 miles 'acceptable.' Class-action settlement reached (Wood, et al. v. FCA US, LLC). CSN W80 warranty extension: 7 years/100,000 miles.
Dodge Durango(1 issue)
- Plenum Gasket Failure (5.2L/5.9L Magnum V8)1998-2003
The plenum gasket between the intake manifold and engine block fails, allowing engine oil to be sucked into combustion chambers. Causes excessive oil consumption, pinging, and visible oily sheen inside intake manifold through throttle body. Common on all 5.2L and 5.9L Magnum V8 engines.
Dodge Stealth(1 issue)
- Active Exhaust System (AES) Valve Failure1991-1996
The Dodge Stealth (particularly RT/TT and ES models) features an Active Exhaust System with electronically controlled valves that open at higher RPM to reduce backpressure. These valves seize from rust and carbon buildup, causing restricted exhaust flow, reduced power, and a check engine light. The vacuum-actuated system uses solenoids and diaphragms that also fail with age. Many owners simply remove the system entirely and replace with a straight-through exhaust, which provides better performance and eliminates the failure point. The AES is shared with the Mitsubishi 3000GT as both cars were built on the same platform.
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View P0420 across all makes →Frequently Asked Questions
What does P0420 mean on Dodge?▼
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 Dodge specifically, this code is documented across 5 models.
What causes P0420 on Dodge vehicles?▼
Common causes on Dodge: 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 Dodge?▼
Repair costs on Dodge range from $200 to $8,500, depending on the specific model and root cause.
Which Dodge models have P0420 documented?▼
Au7o has documented P0420 on 5 Dodge models: Challenger, Dakota, Dart, Durango, Stealth.