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Visual Inspection and Diagnostic Pre-checks

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CAUTION: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may cause damage to the connector.
Fig 1: Antilock Braking System (ABS) Module Connector - C135
GFDWR56215Courtesy of FORD MOTOR COMPANY

Harness Side

Circuit Pin
VREF (Reference Voltage) - LCA37 5 (YELLOW/ORANGE)
SRef (Signal Reference Voltage) - VCA38 37 (BROWN/VIOLET)
SIGRTN (Signal Return) - RCA37 10 (WHITE/BLUE)
Fig 2: Brake Booster Vacuum Sensor Connector - C149
G13342429Courtesy of FORD MOTOR CO.
Circuit Pin
VREF (Reference Voltage) - LCA37 3 (YELLOW/ORANGE)
SRef (Signal Reference Voltage) - VCA38 1 (BROWN/VIOLET)
SIGRTN (Signal Return) - RCA37 2 (WHITE/BLUE)
  1. CA1: CHECK THE BRAKE BOOSTER AND VACUUM HOSES FOR LEAKS 
    • Ignition OFF.
    • Verify all vacuum hoses are fully seated and connected to their respective ports.
    • Inspect the following items for leaks:
      • brake booster body (shell)
      • brake booster-to-master cylinder seal
      • brake booster shell at the master cylinder seal
      • brake booster-to-bulkhead seal
      • brake booster vacuum sensor seal
      • brake booster-to-vacuum pump hose (if equipped)
    • Are all the hoses connected and are all items free of any leaks? 
    Yes No
    Go to  CA2. CONNECT or INSTALL new components as necessary.
  2. CA2: CHECK THE BRAKE BOOSTER 
    • Carry out the Component Test - Brake Booster in the Brake System General Information Diagnosis and Testing article.
    • Did the brake booster pass the component test? 
    Yes No
    Go to  CA3. INSTALL a new brake booster. REFER to the Power Brake Actuation article.
  3. CA3: CHECK FOR OTHER ABS MODULE DTCS 
    • Ignition ON, engine OFF.

      Carry out the ABS self-test.

    • Are any brake pedal position, hydraulic pressure sensor or battery voltage DTCs present in the ABS module? 
    Yes No
    DIAGNOSE all ABS module brake pedal position, hyraulic pressure sensor and battery voltage DTCs before diagnosing any C101A:xx DTCS. Go to  CA4.
  4. CA4: VERIFY ALL WIRING CONNECTIONS 
    • Ignition OFF.
    • ABS Module connector disconnected. (C135)
    • Brake Booster Vacuum Sensor connector disconnected. (C149)
    • Using a good light source, inspect each connector terminal for any corrosion.
    • Inspect both connectors for any pushed-out pins.
      • Refer to the OEM Connector Repair Procedures article for schematic and connector information.
    • Using a suitable mating terminal, check each female terminal for deformed or enlarged contacts by comparing the mating terminal's fit between each of the following pins:
      • C135-5
      • C135-10
      • C135-37
      • C1799-1
      • C1799-2
      • C1799-3
    • Are both connectors free of corrosion, pushed-out pins and deformed or enlarged contacts? 
    Yes No
    Go to  CA5. REPAIR the affected terminal.
    Refer to the OEM Connector Repair Procedures article for schematic and connector information.
  5. CA5: RECHECK THE ABS MODULE FOR DTCS 
    • Brake Booster Vacuum Sensor connector connected. (C149) Make sure the connector seats and latches correctly.
    • ABS Module connector connected. (C135) Make sure the connector seats and latches correctly.
    • Ignition ON, engine OFF.
    • Clear the ABS DTCs.
    • Ignition OFF.
    • Start the engine and allow it to run for at least 1 minute to build up vacuum in the brake booster.
    • Fully and firmly, press and release the brake pedal 3 times.

      Carry out the ABS self-test.

    • Are any C101A:xx DTCs present? 
    Yes No
    Go to  CA6. The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. ADDRESS the root cause of any connector or pin issues.
  6. CA6: CHECK THE VACUUM SENSOR WIRING FOR A SHORT TO VOLTAGE 
    • Ignition OFF.
    • ABS Module connector disconnected. (C135)
    • Brake Booster Vacuum Sensor connector disconnected. (C149)
    • Ignition ON, engine OFF.
    • Measure the voltage between:
      (+) ABS Module (C135) Connector, Harness Side (-)
      VREF - LCA37 (YELLOW/ORANGE) - Pin 5 Ground
      SRef - VCA38 (BROWN/VIOLET) - Pin 37 Ground
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 10 Ground
      VAC GND Ground
      VAC SIG Ground
      VAC SNS P Ground
    • Is any voltage present? 
    Yes No
    REPAIR the circuit. Go to  CA7.
  7. CA7: CHECK THE VACUUM SENSOR WIRING FOR A SHORT TO GROUND 
    • Ignition OFF.
    • Measure the resistance between:
      (+) Brake Booster Vacuum Sensor (C149) Connector, Harness Side (-)
      VREF - LCA37 (YELLOW/ORANGE) - Pin 3 Ground
      SRef - VCA38 (BROWN/VIOLET) - Pin 1 Ground
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 2 Ground
      VAC GND Ground
      VAC SIG Ground
      VAC SNS P Ground
    • Are the resistances greater than 10, 000 ohms? 
    Yes No
    Go to  CA8. REPAIR the circuit.
  8. CA8: CHECK THE VACUUM SENSOR WIRING FOR AN OPEN 
    • Measure the resistance between:
      (+) ABS Module (C135) Connector, Harness Side (-) Brake Booster Vacuum Sensor (C149) Connector, Harness Side
      VREF - LCA37 (YELLOW/ORANGE) - Pin 5 VREF - LCA37 - Pin 3
      SRef - VCA38 (BROWN/VIOLET) - Pin 37 SRef - VCA38 - Pin 1
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 10 SIGRTN - RCA37 - Pin 2
      VAC GND VAC GND
      VAC SIG VAC SIG
      VAC SNS P VAC SNS P
    • Are the resistances less than 3 ohms? 
    Yes No
    Go to  CA9. REPAIR the circuit.
  9. CA9: CHECK THE VACUUM SENSOR WIRING FOR A SHORT TOGETHER 
    • Measure the resistance between:
      (+) Brake Booster Vacuum Sensor (C149) Connector, Harness Side (-) Brake Booster Vacuum Sensor (C149) Connector, Harness Side
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 2 SRef - VCA38 - Pin 1
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 2 VREF - LCA37 - Pin 3
      SRef - VCA38 (BROWN/VIOLET) - Pin 1 VREF - LCA37 - Pin 3
      VAC GND VAC SIG
      VAC GND VAC SNS P
      VAC SIG VAC SNS P
    • Are the resistances greater than 10, 000 ohms? 
    Yes No
    For DTC C101A:1C, Go to  CA10.
    For all others, INSTALL a new Brake Booster Vacuum Sensor.
    REFER to the Power Brake Actuation article.    		 REPAIR the circuit.
  10. CA10: CHECK THE ABS MODULE OUTPUT 
    • ABS Module connector connected. (C135) Make sure the connector seats and latches correctly.
    • Ignition ON, engine OFF.
    • Measure the voltage between:
      (+) Brake Booster Vacuum Sensor (C149) Connector, Harness Side (-)
      VREF - LCA37 (YELLOW/ORANGE) - Pin 3 Ground
      VAC SNS P Ground
    • Is the voltage between 4.7 and 5.2 volts? 
    Yes No
    INSTALL a new Brake Booster Vacuum Sensor.
    REFER to the Power Brake Actuation article.    		 Go to  CA11.
  11. CA11: CHECK FOR CORRECT ABS MODULE OPERATION 
    • Ignition OFF.
    • Brake Booster Vacuum Sensor connector connected. (C149) Make sure the connector seats and latches correctly.
    • Operate the system and determine if the concern is still present.
    • Is the concern still present? 
    Yes No
    INSTALL a new ABS module.
    CHECK OASIS for any service articles: TSB, GSB
    (general service bulletin), SSM (special service message) or FSA (Field Service Action).
    If a service article exists for this concern, DISCONTINUE this test and FOLLOW the service article instructions.
    If no service articles address this concern, INSTALL a new ABS module. REFER to the Anti-Lock Brake System (ABS) and Stability Control article.
    ORDER a replacement ABS module and INCLUDE the RVC on the form.
    If this is a Ford paid repair, INCLUDE the RVC on the warranty claim form.    		 The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. ADDRESS the root cause of any connector or pin issues.
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