P0412–P0415 AIR System Switching Valve A Circuit
The ECU has logged a fault on P0412. The definition below is the exact wording the standard uses for this code.
Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
P0412 | AIR System Switching Valve A Circuit | Investigate soon |
P0415 | AIR System Switching Valve B Circuit | Investigate soon |
The definition
P0412: AIR System Switching Valve A Circuit.
P0412 is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.
What to check first
Cheapest and fastest checks first:
- Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
- Check the connector at the part for corrosion, and that it is fully seated.
- Clear the code and see whether it returns, and under what conditions.
What actually causes this on a VAG
This one is purely electrical, and it's about the small solenoid changeover valve rather than the air pump. On most VAG engines that valve (usually listed as N112 in diagnostic software) doesn't handle the injected air itself - it switches vacuum through to open the combi valve on the cylinder head. P0412 means the ECU's output circuit to that solenoid isn't behaving as it expects. It's usually one of the cheaper faults in the secondary air system.
Most likely causes, in order
- Connector or wiring fault. The valve sits in a warm, exposed spot and its plug is easy to knock off during other work. Look for corroded pins, a connector that isn't clipped home and chafed insulation, then wiggle-test the plug while an output test is running. It costs nothing, so start here.
- Failed solenoid. Age and under-bonnet heat eventually kill the winding. The valve should click audibly when it's commanded in an output test; no click, and no continuity across its two pins, means it's finished. Worth knowing that the solenoid is one of the less common things to fail in this system, so don't jump to it before checking the plug.
- Lost supply or fuse. The solenoid's power comes from a feed shared with other actuators, so a blown fuse or a poor supply joint can knock out several things at once. If other actuator codes have stored alongside this one, chase the shared feed rather than the valve.
Worth knowing: Fixing the electrical fault doesn't automatically mean air is reaching the exhaust again. This valve's job is switching vacuum, so check its vacuum hoses at the same time - a healthy solenoid with a split hose logs no electrical fault at all, and you'll simply be back with a flow code like P0411 instead.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
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Common questions
What does P0412 mean?
P0412 means AIR System Switching Valve A Circuit. It is logged when the ECU sees this circuit outside its expected operating window.
Can I drive with P0412?
The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.