A fault in the secondary air system can usually be identified by a scratching or whistling noise, or by the secondary air pump no longer working. For vehicles with OBD, a diagnostic trouble code may also be saved in the engine control unit.
Tip 1: Test the electrical actuation of the secondary air pump by the engine control unit and the switching relay.
The function test for the secondary air pump can be performed when the engine is cold, as the pump will then be audible for up to 90 seconds. However, the test can also be carried out with the engine at operating temperature using a diagnostic tester or an external 12 volt voltage source. If no malfunction is identified, the following problems should be ruled out: signs of melting on the housing or on the plug contacts of the secondary air pump and/or a strong smell of burning. In these cases, it is essential to replace the switching relay.
Tip 2: Frequent causes of failure are water or exhaust gas condensate in the secondary air pump. This firstly causes loud noises and then leads to failure. Clear water or rust signal a leakage between the air filter and secondary air pump.
Tip 3: Exhaust gas condensate can only enter the pump through the secondary air valve, caused by the secondary air valve becoming stuck and no longer fully closing. You can use your finger to check whether there are any deposits. If there are deposits, this means the secondary air valve is faulty and must be replaced.
Tip 4: When it comes to pneumatically actuated secondary air valves, the solenoid valve being actuated and the vacuum should be checked. If a vacuum of at least 390 mbar is not reached, it is highly likely that there are leakages.