P0420 on Mitsubishi
Catalyst System Efficiency Below Threshold (Bank 1)
P0420 on Mitsubishi vehicles indicates catalyst system efficiency below threshold (bank 1). Au7o has documented this code across 1 Mitsubishi model — most commonly on Eclipse. 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 Mitsubishi range from $300 to $2,500, 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 Mitsubishi by Model
Mitsubishi Eclipse(1 issue)
- V6 Engine Oil Consumption2000-2012
The 3.0L 6G72 and 3.8L 6G75 V6 engines in the Eclipse GT develop excessive oil consumption over time. Worn valve stem seals and piston ring glazing allow oil to enter the combustion chambers, producing blue exhaust smoke and requiring frequent top-offs.
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View P0420 across all makes →Frequently Asked Questions
What does P0420 mean on Mitsubishi?▼
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 Mitsubishi specifically, this code is documented across 1 model.
What causes P0420 on Mitsubishi vehicles?▼
Common causes on Mitsubishi: 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 Mitsubishi?▼
Repair costs on Mitsubishi range from $300 to $2,500, depending on the specific model and root cause.
Which Mitsubishi models have P0420 documented?▼
Au7o has documented P0420 on 1 Mitsubishi model: Eclipse.