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Possible Causes

WARNING: This page is about a different car, the 2018 Lincoln MKC. However, it is still accessible from the selected car via links, so may be relevant.

Visual Inspection and Diagnostic Pre-checks 

Fig 1: Antilock Braking System (ABS) Module Connector - C135
G11915951Courtesy of FORD MOTOR CO.
CONNECTOR PIN REFERENCE (HARNESS SIDE)

Circuit Pin
VREF (Reference Voltage) - LCA37 44 (YELLOW/ORANGE)
SRef (Signal Reference Voltage) - VCA38 36 (BROWN/VIOLET)
SIGRTN (Signal Return) - RCA37 45 (WHITE/BLUE)
Fig 2: Brake Booster Vacuum Sensor Connector - C149
G11915952Courtesy of FORD MOTOR CO.
CONNECTOR PIN REFERENCE (HARNESS SIDE)

Circuit Pin
VREF (Reference Voltage) - LCA37 3 (YELLOW/ORANGE)
SRef (Signal Reference Voltage) - VCA38 1 (BROWN/VIOLET)
SIGRTN (Signal Return) - RCA37 2 (WHITE/BLUE)

Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may cause damage to the connector.

  1. CA1: 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, hydraulic pressure sensor and battery voltage DTCs before diagnosing any C101A:xx DTCS. Go to  CA2.
  2. CA2: VERIFY ALL WIRING CONNECTIONS 
    • Ignition OFF.
    • ABS Module connector disconnected. (C135)
    • Brake Booster Vacuum Sensor connector disconnected. (C149)
    • Disconnect all in-line electrical connectors between the ABS module and the brake booster vacuum sensor.
    • Using a good light source, inspect each connector terminal for any corrosion.
    • Inspect both connectors for any pushed-out pins.
    • Are both connectors free of corrosion, pushed-out pins and deformed or enlarged contacts? 
      Yes No
      Go to  CA3. REPAIR the affected terminal.
      Refer to OEM Connector Repair Procedures
  3. CA3: RECHECK THE ABS MODULE FOR DTCS 
    • Connect all in-line electrical connectors between the ABS module and the brake booster vacuum sensor. Make sure they seat and latch correctly.
    • 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  CA4. 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.
      If this is a Ford paid repair, INCLUDE the RVC on the warranty claim form.
  4. CA4: 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 44 Ground
      SRef - VCA38 (BROWN/VIOLET) - Pin 36 Ground
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 45 Ground
    • Is any voltage present? 
      Yes No
      REPAIR the circuit. Go to  CA5.
  5. CA5: 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
    • Are the resistances greater than 10, 000 ohms? 
      Yes No
      Go to  CA6. REPAIR the circuit.
  6. CA6: 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
      SRef - VCA38 (BROWN/VIOLET) - Pin 36 SRef - VCA38 - Pin 1
      SIGRTN - RCA37 (WHITE/BLUE) - Pin 45 SIGRTN - RCA37 - Pin 2
    • Are the resistances less than 3 ohms? 
      Yes No
      Go to  CA7. REPAIR the circuit.
  7. CA7: 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
    • Are the resistances greater than 10, 000 ohms? 
      Yes No
      For DTC C101A:1C, Go to  CA8.
      For all others,
      INSTALL a new Brake Booster Vacuum Sensor.
      REFER to Power Brake Actuation - Brake Booster .      		 REPAIR the circuit.
  8. CA8: CHECK THE ABS MODULE OUTPUT 
    • Connect all in-line electrical connectors between the ABS module and the brake booster vacuum sensor.
      • Make sure the connectors seat and latch correctly.
    • 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
    • Is the voltage between 4.7 and 5.2 volts? 
      Yes No
      INSTALL a new Brake Booster Vacuum Sensor.
      REFER to Power Brake Actuation - Brake Booster .      		 Go to  CA9.
  9. CA9: 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 applicable Technical Service Bulletins TSBs.
      If a TSB exists for this concern, DISCONTINUE this test and FOLLOW the TSB instructions.
      If no TSBs address this concern, INSTALL a new ABS module. REFER to Anti-Lock Brake System (ABS) And Stability Control .
      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.
      When complete, SELECT the "X" in the top right corner to CLOSE this procedure.      		 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.
      If this is a Ford paid repair, INCLUDE the RVC on the warranty claim form.
      When complete, SELECT the "X" in the top right corner to CLOSE this procedure.
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