Fault codeP0422

MODERATE

Main Catalyst Efficiency Below Threshold (Bank 1)

What this code means

Main Catalyst Efficiency Below Threshold (Bank 1).

“Bank 1” is the side of the engine that holds cylinder number 1; “Bank 2” only exists on V and flat engines. An in-line engine has a single bank.

P0422 is a generic code: it means the same thing on every make. P0422 belongs to family P04xx — Emission controls. Its page explains how to read a code and groups all its codes by part.

Catalytic converter

The catalytic converter turns the most harmful exhaust gases into less harmful ones. The control unit judges its efficiency by comparing the oxygen sensors before and after it: a converter in good condition smooths the signal of the downstream sensor.

What you notice

Usually nothing, apart from the warning light; a smell of rotten eggs or a loss of power with a blocked converter.

How to check it

Before condemning the converter, rule out what can kill it or fool the measurement: misfires, a rich mixture, an exhaust leak, an ageing downstream oxygen sensor. Klaro's catalyst temperatures and fuel trims, when the car reports them, help spot an engine running out of balance.

Watch it live in Klaro

With an OBD2 adapter plugged in, these live readings show the part at work, when your car reports them:

O2 sensor voltage, bank 1 sensor 1
O2 sensor voltage, bank 1 sensor 2
Catalyst temp. bank 1 sensor 1
Catalyst temp. bank 1 sensor 2

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

How to read this code

PPowertrain
0standardised code
4Emission controls
22P0422