Possible Causes

WARNING: This page is about a different car, the 2019 Ford F-550 Super Duty, 2019 Ford F-450 Super Duty, 2019 Ford F-350 Super Duty, and 2019 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.

Vacuum hoses
Front hublock IWE vacuum hose connection
Brake master cylinder seal
Bent or damaged booster shell at master cylinder seal
Vacuum tube grommet
Vacuum sensor grommet

CB1: CHECK BRAKE PEDAL FEEL

Ignition ON, engine running.
Press and release the brake pedal at least 3 times.
Does the brake pedal have a hard or firm feel when pressed?

Yes	No
DIAGNOSE the brake booster. REFER to Component Tests in the Brake System General Information article.	Go to CB2.

CB2: CHECK FOR OTHER ABS MODULE DTCS

Ignition ON, engine OFF.
Carry out the ABS self-test.

Carry out the PCM KOEO self-test.
Are any C1015:xx or C101A:xx DTCs present?

Yes	No
For DTC C1015, Go to PINPOINT TEST AH . For DTC C101A, Go to PINPOINT TEST CA .	Go to CB3.

CB3: CHECK THE BRAKE BOOSTER AND VACUUM COMPONENTS

Ignition OFF.
Inspect the following components for signs of obvious damage:
- Vacuum tube grommet
- Vacuum sensor grommet
- Brake master cylinder seal
- Booster shell at master cylinder seal
- Vacuum hoses and tubes
- Brake booster
- Front hublock IWE vacuum hose connection
Are the components listed free from any damage?

Yes	No
Go to CB4.	INSTALL new components as necessary. Go to CB4.

CB4: TEST THE BRAKE BOOSTER

Carry out the Component Test - Brake Booster.
- Refer to Diagnosis and Testing in the Brake System General Information article.
Was the component test successful?

Yes	No
Go to CB5.	INSTALL new components as directed by the component test.

CB5: VERIFY ABS MODULE VACUUM/PRESSURE SENSOR SIGNAL 1 (VAC_PRS_S1) PID

NOTE: Running the engine with the vacuum sensor removed from the brake booster sets DTCs in the ABS module. Clear all DTCs once the repair is complete.

Start the engine and allow to idle for at least 20 seconds.
Access the ABS and monitor the VAC_PRS_S1 (PRESS) PID.
Note the PID display.
Ignition OFF.
Remove the vacuum sensor from the brake booster.
- Leave the electrical connector connected.
Connect a vacuum gauge to the vacuum sensor port.
Start the engine and allow to idle for at least 20 seconds.
Read and record the vacuum gauge display.
Ignition OFF.
Disconnect the vacuum gauge from the brake booster and install the vacuum sensor.
NOTE: 100mbar = 10 kPa = 3 in Hg
Does the VAC_PRS_S1 PID display match the recorded vacuum gauge display ±10 kPa (3 inches Hg)?

Yes	No
The condition causing the concern is not present at this time. The concern may be temperature related. ALLOW the vehicle to remain outside overnight and RETEST the vacuum system.	INSTALL a new Brake Booster Vacuum Sensor. REFER to the Power Brake Actuation article.