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Visual Inspection and Diagnostic Pre-checks

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NOTE: 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 Module Connector (C135)
GFDW79032Courtesy of FORD MOTOR COMPANY
CIRCUIT AND PIN DESCRIPTION

Circuit Pin
VREF (Reference Voltage) - LCA37 44 (YELLOW/ORANGE)
SIGRTN (Signal Return) - RCA37 45 (WHITE/BLUE)
SRef (Signal Reference Voltage) - VCA38 36 (BROWN/VIOLET)
Fig 2: Brake Booster Vacuum Sensor Connector (C149)
G12970680Courtesy of FORD MOTOR CO.
CIRCUIT AND PIN DESCRIPTION

Circuit Pin
SRef (Signal Reference Voltage) - VCA38 1 (BROWN/VIOLET)
SIGRTN (Signal Return) - RCA37 2 (WHITE/BLUE)
VREF (Reference Voltage) - LCA37 3 (YELLOW/ORANGE)
  1. C1: VERIFY ALL WIRING CONNECTIONS 
    • Ignition OFF.
      NOTE: The battery must be removed to access the ABS module electrical connector.
    • Remove the battery. Refer to the appropriate procedure in Battery, Mounting and Cables article
    • 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 OEM GROUND DISTRIBUTION 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:
      • C135-36
      • C135-44
      • C135-45
      • C149-1
      • C149-2
      • C149-3
    • Are both connectors free of corrosion, pushed-out pins and deformed or enlarged contacts? 
      Yes No
      Go to  C2. REPAIR the terminals in question.
  2. C2: CHECK THE ABS MODULE DTCS 
    • ABS Module connector connected. (C135) Make sure the connector seats and latches correctly.
    • Brake Booster Vacuum Sensor connector connected. (C149) Make sure the connector seats and latches correctly.
    • Install the battery. Refer to the appropriate procedure in Battery, Mounting and Cables article
    • Ignition ON, engine OFF.
    • Carry out the ABS self-test.
    • Are any DTCs from the DTC Fault Trigger Conditions Table present? 
      Yes No
      Go to  C3. Go to  C4.
  3. C3: CHECK THE BRAKE BOOSTER AND VACUUM HOSES FOR LEAKS 
    • Inspect the vacuum hoses, brake booster and brake booster seals for leaks or evidence of leaks.
    • Are the vacuum hoses, brake booster and brake booster seals free from leaks? 
      Yes No
      Go to  C4. REPAIR or INSTALL new components as necessary.
  4. C4: CHECK THE VACUUM SENSOR WIRING FOR A SHORT TO VOLTAGE 
    • Ignition OFF.
      NOTE: The battery must be removed to access the ABS module electrical connector.
    • Remove the battery. Refer to the appropriate procedure in Battery, Mounting and Cables article.
    • ABS Module connector disconnected. (C135)
    • Brake Booster Vacuum Sensor connector disconnected. (C149)
    • Install the battery. Refer to the appropriate procedure in Battery, Mounting and Cables article.
    • Ignition ON, engine OFF.
    • Measure the voltage between:
      (+) ABS Module (C135) Connector, Harness Side (-)
      VREF - LCA37 (YELLOW/ORANGE) - Pin 44 Ground
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 45 Ground
      SRef - VCA38 (BROWN/VIOLET) - Pin 36 Ground
      VAC GND Ground
      VAC SIG Ground
      VAC SNS P Ground
    • Measure the voltage between:
    • C5: CHECK THE VACUUM SENSOR WIRING FOR A SHORT TO GROUND 
    • Ignition OFF.
    • Measure the resistance between:
      (+) ABS Module (C135) Connector, Harness Side (-)
      VREF - LCA37 (YELLOW/ORANGE) - Pin 44 Ground
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 45 Ground
      SRef - VCA38 (BROWN/VIOLET) - Pin 36 Ground
      VAC GND Ground
      VAC SIG Ground
      VAC SNS P Ground
    • Measure the resistance between:
  5. C6: 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 44 VREF - LCA37 - Pin 3
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 45 SIGRTN - RCA37 - Pin 2
      SRef - VCA38 (BROWN/VIOLET) - Pin 36 SRef - VCA38 - Pin 1
      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  C8. REPAIR the circuit in question.
  6. C7: CHECK THE VACUUM SENSOR WIRING FOR AN OPEN 
    • Measure the resistance between:
  7. C8: 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
      SRef - VCA38 (BROWN/VIOLET) - Pin 1 SIGRTN - RCA37 - Pin 2
      SRef - VCA38 (BROWN/VIOLET) - Pin 1 VREF - LCA37 - Pin 3
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 2 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
      Go to  C9. REPAIR the circuits in question.
  8. C9: CHECK THE MODULE OUTPUT 
    NOTE: The battery must be removed to access the ABS module electrical connector.
    • Remove the battery. Refer to the appropriate procedure in Battery, Mounting and Cables article.
    • ABS Module connector connected. (C135) Make sure the connector seats and latches correctly.
    • Install the battery. Refer to the appropriate procedure in Battery, Mounting and Cables article.
    • 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 approximately 4.7 volts? 
      Yes No
      INSTALL a new brake booster vacuum sensor. Go to  C10.
  9. C10: VERIFY ALL WIRING CONNECTIONS 
    • Ignition OFF.
      NOTE: The battery must be removed to access the ABS module electrical connector.
    • Remove the battery. Refer to the appropriate procedure in Battery, Mounting and Cables article.
    • ABS Module connector disconnected. (C135)
    • Using a good light source, inspect all disconnected electrical connectors for the following:
      • corrosion - install new connector or terminal and clean the module pins.
      • damaged or bent pins - install new terminals or pins.
      • pushed-out pins - install new pins as necessary.
      • spread terminals - install new terminals as necessary.
    • Are the connectors free of corrosion, damaged pins, bent pins, pushed-out pins and spread terminals? 
      Yes No
      Go to  C11. REPAIR the connector or terminals. Refer to OEM GROUND DISTRIBUTION article, for schematic and connector information.
  10. C11: CHECK FOR CORRECT ABS MODULE OPERATION 
    • Ignition OFF.
    • 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.
    • Install the battery. Refer to the appropriate procedure in Battery, Mounting and Cables article
    • 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 applicable service articles: TSB, GSB, SSM or FSA.
      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 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.
  11. C12: CHECK FOR CORRECT PCM OPERATION 
    • Ignition OFF.
    • Brake Booster Vacuum Sensor connector connected. (C149) Make sure the connector seats and latches correctly.
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