Attention! Do not disconnect the non-return valve from the vacuum hose while doing this.
2. Check the operation of the check valve using a vacuum pump. The valve is healthy if when the pump is connected to the side of the valve going to the brake booster, a vacuum is created and maintained, and when the pump is connected to the side of the valve going to the intake manifold, no vacuum is created.
Attention! If the non-return valve is defective, it must be replaced complete with a vacuum hose.