1. Remove the vacuum hose..
2. Verify that air can be blown from the power brake unit side of the vacuum hose towards the vacuum pump side, and that air cannot be blown in the opposite direction.

If there is any malfunction of the inner check valve, replace it together with the vacuum hose as a single unit.
Vacuum Hose Removal/Installation
Vacuum Pump InspectionFlywheel Inspection [C66 M R]
1. Remove the flywheel..
2. Perform the following procedures to inspect the flywheel.
If there is any malfunction or it exceeds the maximum specification, replace
the flywheel..
a. Inspect the surface that contacts the clutch disc for scratches, nicks, and
discoloration.
...
Thermostat Inspection
1. Remove the thermostat..
2. Visually check that the thermostat valve is closed.
3. Place the thermostat in water.
WARNING:
During inspection, the thermostat and water are extremely hot and can cause
severe burns. Do not touch the thermostat and water.
4. Heat the water and c ...
Front Stabilizer Removal/Installation
CAUTION:
Performing the following procedures without first removing the front ABS
wheel-speed sensor may possibly cause an open circuit in the wiring harness
if it is pulled by mistake. Before performing the following procedures, disconnect
the front ABS wheel-speed sensor wiring ...