Possible Causes
WARNING: This page is about a different car, the 2020 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.
- Vacuum leak
- Vacuum hose obstruction
- Brake booster
- Vacuum pump (if equipped)
- AH1: CHECK THE ABS MODULE DTCS
- Ignition ON, engine OFF.
Carry out the ABS self-test.
- Is DTC C0047:xx, C101A:xx, C1B14:xx, or C1B15:xx also present in the ABS module?
- Ignition ON, engine OFF.
- AH2: CHECK FOR VACUUM LEAKS
- Ignition ON, engine running.
- Inspect the vacuum hose and each hose connection from the engine to the brake booster for leaks.
- Are any vacuum leaks found?
Yes No REPAIR the vacuum leak or INSTALL new components as necessary. Go to AH4.
- AH3: CHECK FOR VACUUM LEAKS
- Ignition ON, engine running.
- Inspect the vacuum hose and each hose connection from the vacuum pump to the brake booster for leaks.
- Are any vacuum leaks found?
Yes No REPAIR the vacuum leak or INSTALL new components as necessary. Go to AH5.
- AH4: CHECK THE VACUUM SUPPLY TO THE BRAKE BOOSTER
- Ignition OFF.
- Disconnect the vacuum hose from the brake booster.
- Connect a vacuum gauge to the vacuum hose.
- Ignition ON, engine running.
- Monitor the vacuum gauge.
- Does the vacuum gauge display a steady reading greater than 600 mBar (18 In-Hg)?
Yes No INSTALL a new brake booster. REFER to the Power Brake Actuation article. DIAGNOSE the engine vacuum concern. CARRY OUT the Intake Manifold Vacuum Test. REFER to Diagnosis and Testing in the Engine System General Information article.
- AH5: CHECK THE VACUUM PUMP OUTPUT
- Ignition OFF.
- Disconnect the vacuum hose from the brake booster.
- Connect a vacuum gauge to the vacuum hose.
- Ignition ON, engine running.
- Monitor the vacuum gauge.
- Does the vacuum gauge display greater than 600 mBar (18 In-Hg)?
Yes No INSTALL a new brake booster. REFER to the Power Brake Actuation article. INSTALL a new vacuum pump. REFER to the appropriate procedure in the Power Brake Actuation article.