Check the check valve - AR43.10-P-0023RT

MODEL 251 

Fig 1: Checking Vacuum Line With Check Valve

Courtesy of MERCEDES-BENZ USA

	Check
1	Open engine hood		AR88.40-P-1000RT
2	Connect vacuum tester (1) to brake booster (3).	Observe manufacturer's operating instructions in order to prevent erroneous measurement or faulty operation! Reduce vacuum of brake pedal beforehand by pressing pedal several times. Do not bend vacuum line excessively. Possibly separate the vacuum line from any fixings on the front end in order to achieve more freedom of movement.	AR43.10-P-0024-01RT
		Test connection	Fig 2
		Vacuum tester	Fig 3
	Risk of accident  caused by vehicle starting off by itself when engine is running. Risk of injury  caused by contusions and burns during starting procedure or when working near engine	Secure vehicle to prevent it from moving. Wear closed and snug-fitting work clothes. Do not grasp hot or rotating parts.	AS00.00-Z-0005-01A
3	Start engine and create a vacuum of 0.75 to 0.8 bar by accelerating and then suddenly releasing the accelerator pedal.	If vacuum is > 0.8 bar, reduce vacuum to 0.75 to 0.8 bar by pressing pedal.
4	Switch off engine and observe the measured value of vacuum on the pressure gauge of the vacuum tester (1)	Vacuum must not drop by more than 0.2 bar within 30 seconds. If the vacuum loss > 0.2 bar the vacuum line with check valve (2) must be replaced. If there are indications of a defective brake booster (3): ↓
		Check brake booster (3)	AR43.10-P-0325RT
5	Disconnect vacuum tester (1) from brake booster (3).		AR43.10-P-0024-01RT
		Test connection	Fig 2
		Vacuum tester	Fig 3
6	Close engine hood		AR88.40-P-1000RT

Fig 2: Identifying Test Connection (168 589 08 63 00)

Courtesy of MERCEDES-BENZ USA

Fig 3: Identifying Vacuum Tester (201 589 13 21 00)

Courtesy of MERCEDES-BENZ USA