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P2438 – Secondary Air Injection System Air Flow/Pressure Sensor Circuit High Bank 2 (OBD2)

P2438 means "Secondary Air Injection System Air Flow/Pressure Sensor Circuit High Bank 2". The voltage in the secondary air injection system circuit is above the permitted maximum. For most sensors this points to an open signal or ground wire – the signal "floats" up to the reference voltage – or to a short to voltage.

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P2438 quick summary

Fault codeP2438
MeaningSecondary Air Injection System Air Flow/Pressure Sensor Circuit High Bank 2
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityLow
Can I drive?Yes. The engine runs normally, but cold-start emissions are higher and the car may fail the emissions test.
Repair cost€20 – €700

How the secondary air injection system works

The secondary air system pumps fresh air into the exhaust for the first minute or two after a cold start, so the catalytic converter heats up faster and cold-start emissions fall.

An electric air pump blows air through a combination (check) valve into the exhaust ports. The extra oxygen burns the rich cold-start exhaust in the manifold, heating the catalytic converter. The check valve prevents exhaust from flowing back into the pump; it is opened by vacuum through a solenoid or by air pressure.

The control unit monitors the system with the oxygen sensors or a pressure sensor: when the pump runs, the oxygen sensor should show a lean signal. If not, it stores flow codes (P0410, P0411, P0491, P0492); other codes cover the switching valves and the pump relay.

The pump often fails because moisture or exhaust gas gets into it through a leaking check valve. Carbon can also block the air passages in the cylinder head. Faults do not affect driving, but the car will not pass an emissions inspection with the Check Engine light on.

Bank 2 is the cylinder row that does NOT contain cylinder 1, so this code only appears on V6, V8, V10, V12 and boxer engines.

Symptoms of P2438

  • Check Engine light on
  • No pump noise after a cold start – or a loud whine/rattle from the pump
  • Usually no driving symptoms
  • Failed emissions test

Most common causes of P2438 (most likely first)

Mechanic's Pro Tip

If the pump is full of water or soot, replace the check valve along with it – a leaking check valve is usually why the pump died, and the new pump would suffer the same fate.

  1. 1.Open circuit in the signal or ground wire

    Most likely

    A loose ground connection is a very common cause.

  2. 2.Signal wire shorted to the 5 V reference or battery voltage

  3. 3.Faulty secondary air injection system

  4. 4.Sticking or leaking check (combination) valve

  5. 5.Cracked air or vacuum hoses

  6. 6.Carbon-blocked air passages in the cylinder head

Step-by-step diagnostic guide

  1. 1

    Read codes

    Read all codes and note whether they concern flow, the switching valves or the relay.

  2. 2

    Check signal and ground

    With the ignition on and the secondary air injection system plugged in, back-probe the signal and ground wires. A signal stuck at reference or battery voltage points to an open ground/signal wire or a short to voltage.

    Multimeter: Ground wire to battery negative: below about 0.1 V. Signal stuck at about 5 V (or 12 V) = open or short to voltage.

  3. 3

    Listen at cold start

    Listen for the pump during the first minute after a cold start. No noise points to the pump, relay or fuse.

  4. 4

    Check relay, fuse and power

    Check the relay and fuse, and measure the supply voltage at the pump when it should run.

  5. 5

    Check valve and hoses

    Check the check valve for exhaust deposits and correct operation, and the hoses for cracks.

    Multimeter: Vacuum-operated valves should open with about 0.3–0.5 bar vacuum and seal when released.

  6. 6

    Run the system test

    Use the scan tool to run the secondary air test and watch the oxygen sensor go lean when the pump runs.

How do I read fault codes? →Where the OBD2 port is, which scanner to use and how to read and clear codes step by step.

Frequently asked questions

Can I keep driving with P2438?

Yes. The engine runs normally, but cold-start emissions are higher and the car may fail the emissions test.

How much does it cost to fix P2438?

Typical repair costs are 20 € – 700 €, depending on the cause and the vehicle. The most common fixes are: open circuit in the signal or ground wire; signal wire shorted to the 5 V reference or battery voltage; faulty secondary air injection system. Always confirm the cause with the tests above before buying parts.

Is the secondary air system necessary?

Yes, for emissions approval. Disabling it is illegal and the Check Engine light will stay on.

Why does the pump only run for a minute?

It is only needed while the catalytic converter warms up after a cold start.

What is the difference between P2438 and similar codes?

P2438 belongs to a group of codes for the same component that differ in the type or location of the fault: P2435 – Secondary Air Injection System Air Flow/Pressure Sensor Circuit Bank 2; P2436 – Secondary Air Injection System Air Flow/Pressure Sensor Range/Performance Bank 2; P2437 – Secondary Air Injection System Air Flow/Pressure Sensor Circuit Low Bank 2; P2439 – Secondary Air Injection System Air Flow/Pressure Sensor Circuit Intermittent Bank 2; P2440 – Secondary Air Injection System Switching Valve Stuck Open Bank 1; P2441 – Secondary Air Injection System Switching Valve Stuck Closed Bank 1. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.