P0422 Code Meaning and Next Steps

First checks take 10 to 20 minutes for the first checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The engine starts running much worse, stalls, or the warning light flashes.
!The vehicle begins to overheat, knock, or lose power sharply while the code is active.

If the light is steady and the vehicle still drives normally: Often yes for a short time, but it should not be ignored.

What to check first

Step-by-step checks

1
Free - no tools
Check for misfire, fuel-trim, or oxygen-sensor codes that could affect catalyst efficiency
2
Free - no tools
Inspect the exhaust for leaks ahead of the catalyst and around sensor bungs
3
Basic tool needed
Notice whether the engine runs rough, smells rich, or loses power under load
4
Basic tool needed
If scan data is available, compare upstream and downstream oxygen-sensor behavior before replacing the converter
5
Basic tool needed
If the engine is not running cleanly, solve that first because the catalyst may be the victim rather than the cause

If the code returns

-If upstream faults are present, address them before condemning the converter.
-If the exhaust is sealed and the engine runs well, the catalyst becomes a stronger suspect.
-If the code returns after a repair, recheck catalyst warm-up and sensor behavior.

Background

What this code means

P0422 is a generic OBD-II code for main catalyst efficiency below threshold on bank 1.

That often points to a tired converter, but the engine needs to be checked first so a fueling or exhaust leak problem is not mistaken for a failed catalyst.

Diagnosis

Common causes

Most common

Aged catalytic converter

The converter may no longer clean exhaust effectively.

Common

Exhaust leak

Fresh air entering upstream can make catalyst efficiency look worse.

Common

Upstream fuel or misfire issue

The converter may be reacting to a problem before it.

Possible

Oxygen sensor bias

A sensor fault can make the converter look less effective than it is.

Avoid these mistakes

What not to do

xDo not replace the sensor or valve first if there is obvious wiring, connector, or vacuum damage.
xDo not ignore drivability changes just because the code sounds like an emissions fault.

Parts

Parts that may need replacing

PartTypical costNotes

Catalytic converter$300-$1500Relevant when upstream faults are ruled out and efficiency is still low.

Exhaust gasket or leak repair$20-$250Worth checking before replacing the converter.

Oxygen sensor$50-$180Useful if sensor data is not trustworthy.

Related OBD codes

P0421

P0421 usually means the warm-up catalyst on bank 1 is not reaching efficiency quickly enough.

P0423

P0423 usually means the heated catalyst on bank 1 is not working efficiently.

P0300

P0300 usually means the engine is detecting random or multiple-cylinder misfires.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0422 was expanded around common catalyst-efficiency faults, especially catalyst wear, exhaust leaks, and upstream fueling issues.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0422 - P0422 Usually Means the Main Catalyst on Bank 1 Is Not Efficient Enough