Brake Booster Check Valve

Replace the brake booster check valve to restore proper vacuum assist function and prevent brake pedal hardness or hissing noises.

Warnings

Tools required

Parts

• Brake booster check valve with grommet × 1 — Motorcraft YH-1829 or equivalent

Preparation

1. Ensure engine is OFF and cool to the touch
2. Open hood and secure with prop rod
3. Locate the brake booster on the driver's side firewall behind the master cylinder
4. Identify the vacuum hose connection on the front of the brake booster with the check valve installed
5. Clear any tools or components from the work area for adequate access

Procedure

1. 1

   Locate and inspect check valve
   The check valve is located on the brake booster body where the vacuum line from the intake manifold connects. On the 5.0L Coyote engine, the vacuum line runs from the passenger side of the intake manifold across to the driver side booster. Use a flashlight to clearly identify the check valve at the booster connection point. Inspect the vacuum hose for cracks or damage while accessible.
2. 2

   Disconnect vacuum hose from check valve
   Grasp the vacuum hose firmly near the check valve connection. Gently twist and pull the hose straight off the check valve. If the hose is stuck due to age, carefully work it back and forth while pulling. Avoid using excessive force that could damage the hose barb. If the hose is severely deteriorated, plan to replace it as well.
3. 3

   Remove old check valve from booster
   The check valve is pressed into a rubber grommet in the brake booster housing. Grasp the check valve body firmly with your hand or needle-nose pliers. Twist the valve approximately 1/4 turn while pulling straight out from the booster. The valve and grommet should come out together. If the valve is stuck, gently pry around the grommet edge with a flat-blade screwdriver while pulling on the valve. Do not pry against the booster housing as it can be damaged.
4. 4

   Inspect booster mounting hole
   With the check valve removed, inspect the mounting hole in the brake booster. Remove any debris or remnants of the old grommet. The mounting hole should be clean and free of damage. If the old grommet remained in the booster, carefully extract it using needle-nose pliers or a small pick tool, being careful not to scratch or damage the booster housing.
5. 5

   Verify new check valve orientation
   Before installation, identify the correct orientation of the new check valve. The valve allows airflow in only one direction. The tapered or marked end typically faces toward the booster (into the housing), while the hose connection end faces outward. Check the valve by blowing through it both directions - air should flow freely toward the booster but not back out. Consult the replacement part packaging for specific orientation instructions if unsure.
6. 6

   Install new check valve assembly
   Ensure the new grommet is properly seated on the check valve body. Align the check valve with the mounting hole in the brake booster, ensuring correct orientation with the hose barb facing outward. Press the valve and grommet assembly firmly and evenly into the booster housing. Push until the grommet seats completely flush with the booster surface. You should feel the grommet snap into place. Tug gently on the valve to confirm it is secure.
7. 7

   Reconnect vacuum hose
   Press the vacuum hose firmly onto the check valve barb until it is fully seated. The hose should slide past any retaining barbs on the valve. Tug on the hose to verify a secure connection. The hose should not pull off easily. Ensure the hose routing is correct with no kinks or sharp bends that could restrict vacuum flow.
8. 8

   Perform initial function test
   Start the engine and listen for any hissing sounds from the brake booster area that would indicate a vacuum leak. The engine should idle smoothly. With the engine running, press the brake pedal several times. The pedal should feel firm with normal assist. If the pedal is hard or there is hissing, immediately shut off the engine and recheck the check valve installation and hose connections.

Reassembly

1. No disassembly was required for this procedure beyond the check valve removal

Verification

• With engine running, verify no hissing sounds from the brake booster or vacuum hose connections indicating vacuum leaks
• Confirm engine idles smoothly with no rough running or check engine light caused by vacuum leak
• Press brake pedal with engine running - pedal should provide normal power-assist feel and require moderate pressure
• Turn off engine and wait 30 seconds, then press brake pedal - you should get 2-3 assisted pedal applications before pedal becomes hard (this confirms check valve is holding vacuum)
• Perform a low-speed test drive in a safe area to confirm normal brake assist function before returning to regular operation
• If brake pedal is excessively hard, engine runs rough, or hissing is present, do not drive the vehicle and recheck all connections immediately

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

Chasing one of these codes and not sure which part is guilty? Ask a master mechanic about YOUR car →

More procedures for this vehicle