Checking Relief Valve
WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect the rubber hose to the relief valve and start the engine.
Check that no engine exhausts flow backwards into the pump.
If exhaust gases flow backwards the relief valve is defective and should be changed.
In connection with this test use compressed air to clean the system to the engine with the engine running .