Secondary Air Injection System Switching Valve A Circuit Malfunction
The P0412 code means the vehicle's onboard diagnostic system has detected: Secondary Air Injection System Switching Valve A Circuit Malfunction. This is a low severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $100 - $350 (parts and labor)
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Common Symptoms
- Check Engine Light illuminated
- No noticeable drivability issues
- Air pump may run longer than normal
- Failed emissions test
Probable Causes (Ranked by Likelihood)
- Faulty air injection switching valve solenoid Very High
- Open or short in switching valve wiring High
- Corroded switching valve connector Moderate
- Failed relay or fuse for switching valve circuit Low
Common Fixes by Vehicle
What techs usually find when diagnosing P0412 on specific vehicles — tap your vehicle for the fix and the exact part:
2006-2014 Volkswagen/Audi 2.0T & 2.5L moderate DIY
Secondary air injection valve A circuit fault is usually a stuck combi-valve or a failed secondary air pump. These only run on cold start. Check the combination valve for carbon sticking and the pump for water intrusion. Many owners replace the combi-valve first since it is far cheaper than the pump.
Labor: 1-2 hoursFrequently Asked Questions
Can I drive with code P0412?
Yes. The switching valve circuit issue does not affect normal driving. The secondary air system only operates during cold starts and is not needed for engine operation.
What is the secondary air switching valve?
The switching valve directs airflow from the secondary air pump to the correct exhaust port. It is typically a vacuum or electrically operated valve that opens during cold starts.
Is P0412 common on European cars?
Yes. BMW, Volkswagen, and Audi vehicles are particularly prone to secondary air system faults including P0412, often due to moisture damage and corrosion of the switching valve.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Locate the secondary air switching valve and inspect the electrical connector
-
Measure solenoid resistance -- compare to manufacturer specification
-
Check for voltage at the connector when the ECM commands the valve on
-
Inspect wiring from the ECM to the switching valve for damage
-
Test the switching valve by applying 12V directly -- it should click and actuate
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- 2001-2012 BMW 325i/330i
- 2003-2015 Volkswagen Passat
- 2002-2010 Audi A4
- 2004-2014 Subaru Impreza
- 2005-2016 Toyota 4Runner
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