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P0415 – Secondary Air Injection System Switching Valve B Circuit Malfunction (OBD2)

P0415 means "Secondary Air Injection System Switching Valve B Circuit Malfunction". The control unit has detected a fault in the electrical circuit of the secondary air injection system: the signal or control current is missing or outside the expected window. The code does not say whether the value is too high or too low, so the wiring and the component itself both have to be checked.

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P0415 quick summary

Fault codeP0415
MeaningSecondary Air Injection System Switching Valve B Circuit Malfunction
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.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16799 (P0415). Both numbers mean the same fault.

Symptoms of P0415

  • 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 P0415 (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.Damaged wire or loose, corroded connector at the secondary air injection system

    Most likely

    Green or white corrosion, pushed-back pins and chafed insulation near hot or moving parts are the most common findings.

  2. 2.Faulty secondary air injection system

    An internal break or short in the component itself.

  3. 3.Blown fuse or missing supply voltage

    If several codes appeared at the same time, check the shared fuse, relay or ground point first.

  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 the circuit with a multimeter

    With the ignition off, unplug the secondary air injection system and the control unit connector (or back-probe), then check each wire between them for continuity and for shorts to ground and to battery voltage. Compare the component's resistance or supply voltage with the value in the repair manual.

    Multimeter: Wire continuity: below about 1 Ω. Wire to ground with both connectors unplugged: no continuity. Supply/reference with ignition on: usually 5 V for sensors, battery voltage for actuators.

  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.

Frequently asked questions

Can I keep driving with P0415?

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 P0415?

Typical repair costs are 20 € – 700 €, depending on the cause and the vehicle. The most common fixes are: damaged wire or loose, corroded connector at the secondary air injection system; faulty secondary air injection system; blown fuse or missing supply voltage. 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 P0415 and similar codes?

P0415 belongs to a group of codes for the same component that differ in the type or location of the fault: P0412 – Secondary Air Injection System Switching Valve A Circuit Malfunction; P0413 – Secondary Air Injection System Switching Valve A Circuit Open; P0414 – Secondary Air Injection System Switching Valve A Circuit Shorted; P0416 – Secondary Air Injection System Switching Valve B Circuit Open; P0417 – Secondary Air Injection System Switching Valve B Circuit Shorted; P0418 – Secondary Air Injection System Relay A circuit Malfunction. 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.