Checking Cylinder For Leakage

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. However, it is still accessible from the selected car via links, so may be relevant.

The engine should be run to operating temperature so that the thermostat is open
The piston in the cylinder that is being checked must be set to top dead center (TDC) at the compression phase
A metered air pressure is connected to the relevant cylinder via an adapter that is secured in the spark plug / glow plug well
A gauge is used to measure the size of the leakage from the cylinder.
This is a pressure sensor with a regulator and displays the size of the leak expressed as a percentage.

This allows the extent of any problem to be determined.