Health check
1. Turn on the ignition and disconnect the black/yellow wire contact from each valve in turn. When the contact is broken, you can hear the click of the valve. If any of the valves are left open, then the engine will probably continue to run even when the ignition is off.
2. Before checking that the valves close properly while the machine is braking, it is necessary to raise and firmly place the vehicle on stands so that the drive wheels can rotate freely. Disconnect the wire from one of the valves and connect a voltmeter between the black/yellow wire and ground.
3. Start the engine and let it warm up to operating temperature. With the rear wheels blocked, shift the transmission into second gear and bring the engine speed up to 2000 rpm. At the moment the accelerator pedal is released, the voltage across the disconnected valve should instantly drop to zero.