7) Check wastegate and blow-off valve

If a wastegate or a blow-off valve does not close, i.e. is stuck open, sufficient charging pressure cannot normally be built up. Wastegates that are stuck closed normally generate overcharge faults; blowoff valves are normally indicated by noise (fluttering). The wastegates are closed through vacuum. For this, -300hPa must be sufficient. If the wastegates first close at low pressures, they are stiff. For additional wear, the flaps no longer close completely or jam in their seat. The blow-off valves are supplied with vacuum by means of an electropneumatic pressure converter and thus opened.