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P0416 – Secondary Air Injection System Switching Valve B Circuit Open (OBD2)

P0416 means "Secondary Air Injection System Switching Valve B Circuit Open". The control unit sees an open circuit: the electrical connection to the secondary air injection system is interrupted, so no current can flow when the component is commanded or read.

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P0416 quick summary

Fault codeP0416
MeaningSecondary Air Injection System Switching Valve B Circuit Open
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.

Symptoms of P0416

  • 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 P0416 (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.Unplugged, loose or corroded connector

    Most likely

    Often after previous repair work in the area.

  2. 2.Broken wire in the harness

    Typical at bends, near the engine mounts and where the harness rubs on brackets.

  3. 3.Burnt-out winding or internal break in the secondary air injection system

  4. 4.Failed secondary air pump

    Moisture or exhaust gas damages the motor.

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

  6. 6.Faulty pump relay, fuse or switching valve

  7. 7.Cracked air or vacuum hoses

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

    Measure resistance and continuity

    Unplug the secondary air injection system and measure its resistance across the terminals. An infinite (OL) reading confirms an internal break. If the component is fine, check each wire back to the control unit for continuity.

    Multimeter: Solenoids and heaters typically read a few ohms to a few dozen ohms; "OL" means open. Wire continuity: below about 1 Ω.

  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 P0416?

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 P0416?

Typical repair costs are 20 € – 700 €, depending on the cause and the vehicle. The most common fixes are: unplugged, loose or corroded connector; broken wire in the harness; burnt-out winding or internal break in the 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 P0416 and similar codes?

P0416 belongs to a group of codes for the same component that differ in the type or location of the fault: P0413 – Secondary Air Injection System Switching Valve A Circuit Open; P0414 – Secondary Air Injection System Switching Valve A Circuit Shorted; P0415 – Secondary Air Injection System Switching Valve B Circuit Malfunction; P0417 – Secondary Air Injection System Switching Valve B Circuit Shorted; P0418 – Secondary Air Injection System Relay A circuit Malfunction; P0419 – Secondary Air Injection System Relay B 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.