Faulty secondary air injection pump (35% likelihood): The air pump has worn out or moisture from exhaust has damaged it internally, reducing airflow below what the sensor expects. Defective one-way check valve (25% likelihood): The check valve that prevents exhaust gases from flowing back into the air pump is stuck or leaking, allowing hot exhaust to damage the pump and alter airflow readings. Faulty air flow or pressure sensor (20% likelihood): The sensor that monitors secondary air injection flow or pressure in Bank 1 has drifted out of calibration or failed. Clogged or restricted air injection passages (15% likelihood): Carbon buildup in the air injection passages or ports in the exhaust manifold restricts airflow, causing out-of-range sensor readings. Wiring or connector issue for the sensor (5% likelihood): Damaged wiring or corroded connectors to the airflow/pressure sensor can cause erratic or out-of-range readings.

How much does it cost to fix P2431?

DIY repair typically costs $50–$250 for parts. Professional repair runs $250–$700 including parts and labor.

P2431

Powertrain

Moderate

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

What could P2431 mean for your vehicle?

Add your vehicle to explore possible causes and next checks. AI guidance helps you investigate; it does not confirm a diagnosis.

The P2431 code means the PCM has detected that the secondary air injection system's airflow or pressure sensor on Bank 1 is reading outside its expected range. The secondary air injection (AIR) system pumps fresh air into the exhaust stream during cold engine starts to help the catalytic converter heat up faster and burn off the rich exhaust that cold engines produce.

This system primarily operates during cold starts, so you may notice the most symptoms when first starting your vehicle — rough idle, slow warm-up, or unusual pump noises. In some cases, the engine may stall during the warm-up period. Because the system affects emissions control, your vehicle will fail an emissions test.

A common root cause is moisture from the exhaust damaging the air pump through a failed one-way check valve. When the check valve fails, hot exhaust gases flow backward into the pump, causing corrosion and eventual failure. Start diagnosis by checking the one-way check valve — if exhaust residue is found on the pump side, the valve has failed. This repair can be moderately challenging depending on the vehicle, as components may be in tight spaces. This code is particularly common on Subaru, Toyota, and some European vehicles.

Severity

Moderate — Address SoonThis Week

Symptoms

•Check Engine Light is on
•Rough idle especially when engine is cold
•Extended engine warm-up time
•Unusual noise from air injection pump
•Poor engine performance during cold start
•Possible stalling during warm-up

Likely Causes

Faulty secondary air injection pump35%

The air pump has worn out or moisture from exhaust has damaged it internally, reducing airflow below what the sensor expects.

Defective one-way check valve25%

The check valve that prevents exhaust gases from flowing back into the air pump is stuck or leaking, allowing hot exhaust to damage the pump and alter airflow readings.

Faulty air flow or pressure sensor20%

The sensor that monitors secondary air injection flow or pressure in Bank 1 has drifted out of calibration or failed.

Clogged or restricted air injection passages15%

Carbon buildup in the air injection passages or ports in the exhaust manifold restricts airflow, causing out-of-range sensor readings.

Wiring or connector issue for the sensor5%

Damaged wiring or corroded connectors to the airflow/pressure sensor can cause erratic or out-of-range readings.