P2431 Code: Secondary Air Injection System Air Flow/Pressure Sensor Circuit Range/Performance (Bank 1)

What the P2431 code means

The secondary air system injects fresh air into the exhaust during the first minutes after a cold start. That burns off leftover hydrocarbons and warms the catalytic converter sooner. It is made up of an electric pump, a relay, a switching valve and a check valve next to the exhaust manifold.

The sensor gets a 5 V reference and a ground from the computer and returns a signal between roughly 0.5 and 4.5 V. A range fault, like the P2431 code, tells you the sensor is measuring, but measuring wrong, or that there is a real abnormal condition in the system.

Some engines use a pressure sensor in the air line to confirm that the pump is blowing and that the valve opens.

This kind of fault does not usually give itself up to a multimeter, because electrically everything looks right. You have to compare what the part says with reality: use a gauge, a thermometer or a tachometer, or command the component with the scan tool and see whether the physical result matches the command.

P2431 code symptoms

• Check engine light on.
• The computer cannot verify the secondary air system.

Likely causes of the P2431 code

1. Sensor degraded or out of calibration. It gives believable readings that are wrong.
2. Real abnormal condition. The system is actually working outside normal.
3. High resistance in the connector from corrosion, which shifts the reading.
4. Damaged or clogged port or hose, depending on the type of sensor.

How to diagnose the P2431 code step by step

1. Read the sensor value on the scan tool and compare it with what you expect.
2. Inspect the connector for corrosion, water or loose pins.
3. Check supply and ground with the key on: the reference should be correct and the ground voltage drop should be under 0.1 V.
4. Measure the signal with the connector plugged in and see whether it changes with the operating condition.
5. Do a wiggle test on the harness with the scan tool in graph mode.
6. Check continuity of each wire to the computer, which should be under 1 ohm.

How to fix the P2431 code

• Repair the connector or the wiring.
• Replace the sensor if the tests confirm it is bad.
• Correct the real condition if there is one.
• Clear the codes and verify with a road test.

Technical reference data

• 5 V reference and a signal that changes with the pressure in the air line.
• Approximate values only: check the manufacturer data for your vehicle.

Brand-specific notes

Because the electrical side usually looks fine on this code, a plain multimeter check will not settle it. Compare the sensor reading with the real pressure or airflow before you buy a part.

P2431 on Volkswagen, Audi and BMW

Common on these makes.

Frequently asked questions about P2431