Fault codeP2431

MODERATE

Secondary Air Injection System Air Flow/Pressure Sensor Circuit Range/Performance (Bank 1)

What this code means

Secondary Air Injection System Air Flow/Pressure Sensor Circuit Range/Performance (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.

P2431 is a generic code: it means the same thing on every make. P2431 belongs to family P24xx — Auxiliary emission controls. Its page explains how to read a code and groups all its codes by part.

Type of fault

The signal stays within its electrical limits, but its value is not plausible: it does not match what the control unit expects given the other sensors. The sensor may be drifting with age, but it may also be faithfully measuring a real mechanical problem — a leak, a blockage, an air leak. Replacing the sensor without checking does not always clear the fault.

Secondary air injection

On some petrol engines, an electric pump blows fresh air into the exhaust for the first minute after a cold start. The extra oxygen helps the catalytic converter reach its working temperature faster. A valve opens the air path and prevents exhaust gas from flowing back.

What you notice

Usually nothing in driving; sometimes a pump noise that stays or is missing at cold start, and a failed emissions test.

How to check it

The pump and the check valve often suffer from moisture: condensation corrodes the pump, and a leaking valve lets exhaust into the system. Check the relay, the fuse, the hoses and the pump's operation at cold start: it should be heard running for about a minute.

Watch it live in Klaro

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

Short term fuel trim bank 1
Long term fuel trim bank 1

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
2standardised code
4Auxiliary emission controls
31P2431