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Fault code

P0411 fault code.

This code comes up with one known fault.

Generic code

Code type

Engine and drivetrain

System

Secondary air system flow is abnormal

At a cold start a pump blows fresh air into the exhaust so that the catalytic converter warms up faster. The engine control unit found the amount of that air abnormal.

The code tells you what the control unit measured, not which part has failed. The same code has several possible causes.

Which known faults it comes up with

Secondary air system: pump and combination valve (P0411)

comfort

From the late nineties to around 2006, petrol engines used a secondary air pump to blow fresh air into the exhaust on a cold start, so the catalytic converter reaches operating temperature faster. The impeller of the pump rusts or its bearing seizes, soot clogs the combination valve (N112), and the rubber hoses crack. The control unit then stores the `P0411` code. It barely affects driving, but the engine warning light is on, and the emissions test can fail because of it, and the roadworthiness test with it.

What to check

  • After a cold start watch for 30 to 60 seconds: can you hear the pump droning from the engine bay
  • Check whether the engine warning light is on, and have it read out: P0411 (VAG code 16795) points to this system
  • Ask when the last emissions test was, and whether it passed first time
2 more steps in the write-up

Information, not an expert opinion

We write the descriptions, and we put the source next to them. A person reviews them before they go out. They are still information, not a technical expert opinion.

  • A fault on the list does not mean the car you are looking at has it.
  • A fault missing from the list does not mean the model is fault-free. Write-ups are made model by model. Not all of them are done.
  • You decide whether to buy. This is no substitute for an inspection. That needs a workshop and a history check.
Details in the terms