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Home >> Audi >> 2016 >> S5 Prestige, 2D Convertible >> Repair and Diagnosis >> External Pages >> Different car >> Section 1145 (Abs Guided Routine Testing) >> Pinpoint Tests >> Pinpoint Test CB: Brake Booster Low Vacuum Fault >> Possible Causes

Possible Causes

WARNING: This page is about a different car, the 2018 Lincoln Navigator. However, it is still accessible from the selected car via links, so may be relevant.
  1. 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 BRAKE SYSTEM - GENERAL INFORMATION . Go to  CB2.
  2. 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 C101A:xx DTCs present? 
    Yes No
    GO to PINPOINT TEST CA . Go to  CB3.
  3. 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.
  4. CB4: TEST THE BRAKE BOOSTER 
    Yes No
    Go to  CB5. INSTALL new components as directed by the component test.
  5. 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: 100 mbar = 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 POWER BRAKE ACTUATION - BRAKE BOOSTER .
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