Possible Causes
- Wiring, terminals or connectors
- Brake booster vacuum leak
- Brake booster vacuum sensor
- Brake booster
- ABS module
Visual Inspection and Diagnostic Pre-checks
- Inspect the brake booster for vacuum leaks.
- Inspect the brake booster for any obvious signs of damage.
- Inspect the brake booster vacuum sensor harness and connector of any obvious signs of damage.
- Make sure the brake booster vacuum sensor electrical connector is free from any corrosion or other contaminants.
CONNECTOR PIN REFERENCE (HARNESS SIDE)
| Circuit | Pin |
|---|---|
| VREF (Reference Voltage) - LCA37 | 5 (YELLOW/ORANGE) |
| SIGRTN (Signal Return) - VCA38 | 32 (WHITE/BLUE) |
| SRef (Signal Reference Voltage) - RCA37 | 37 (BROWN/VIOLET) |
CONNECTOR PIN REFERENCE (HARNESS SIDE)
| Circuit | Pin |
|---|---|
| SRef (Signal Reference Voltage) - VCA38 | 1 (BROWN/VIOLET) |
| SIGRTN (Signal Return) - RCA37 | 2 (WHITE/BLUE) |
| VREF (Reference Voltage) - LCA37 | 3 (YELLOW/ORANGE) |
Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may cause damage to the connector.
- C1: VERIFY ALL WIRING CONNECTIONS
- Ignition OFF.
- ABS Module connector disconnected. (C135)
- Brake Booster Vacuum Sensor connector disconnected. (C1799)
- Using a good light source, inspect each connector terminal for any corrosion.
- Inspect both connectors for any pushed-out pins. Refer to OEM CONNECTOR REPAIR PROCEDURES , 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
- C135-32
- 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 C2. REPAIR the terminals in question.
- C2: CHECK THE ABS MODULE DTCS
- 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.
- C4: CHECK THE VACUUM SENSOR WIRING FOR A SHORT TO VOLTAGE
- Ignition OFF.
- ABS Module connector disconnected. (C135)
- Brake Booster Vacuum Sensor connector disconnected. (C1799)
- Ignition ON, engine OFF.
- Measure the voltage between:
(+) (-) ABS Module (C135) Connector, Harness Side VREF - LCA37 (YELLOW/ORANGE) - Pin 5 Ground SIGRTN - VCA38 (WHITE/BLUE) - Pin 32 Ground SRef - RCA37 (BROWN/VIOLET) - Pin 37 Ground - Is any voltage present?
Yes No REPAIR the circuit in question. Go to C5.
- 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 5 Ground SIGRTN - VCA38 (WHITE/BLUE) - Pin 32 Ground SRef - RCA37 (BROWN/VIOLET) - Pin 37 Ground - Are the resistances greater than 10, 000 ohms?
Yes No Go to C6. REPAIR the circuit in question.
- C6: CHECK THE VACUUM SENSOR WIRING FOR AN OPEN
- Measure the resistance between:
(+) (-) ABS Module (C135) Connector, Harness Side Brake Booster Vacuum Sensor (C1799) Connector, Harness Side VREF - LCA37 (YELLOW/ORANGE) - Pin 5 VREF - LCA37 - Pin 3 SIGRTN - VCA38 (WHITE/BLUE) - Pin 32 SIGRTN - RCA37 - Pin 2 SRef - RCA37 (BROWN/VIOLET) - Pin 37 SRef - VCA38 - Pin 1 - Are the resistances less than 3 ohms?
Yes No Go to C7. REPAIR the circuit in question.
- Measure the resistance between:
- C7: CHECK THE VACUUM SENSOR WIRING FOR A SHORT TOGETHER
- Measure the resistance between:
(+) (-) Brake Booster Vacuum Sensor (C1799) Connector, Harness Side Brake Booster Vacuum Sensor (C1799) 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 - Are the resistances greater than 10, 000 ohms?
Yes No Go to C8. REPAIR the circuits in question.
- Measure the resistance between:
- C8: CHECK THE ABS MODULE OUTPUT
- ABS Module connector connected. (C135)
- Ignition ON, engine OFF.
- Measure the voltage between:
(+) (-) Brake Booster Vacuum Sensor (C1799) Connector, Harness Side VREF - LCA37 (YELLOW/ORANGE) - Pin 3 Ground - Is the voltage approximately 4.7 volts?
Yes No INSTALL a new brake booster vacuum sensor. Go to C9.
- C9: CHECK FOR CORRECT ABS MODULE OPERATION
- Ignition OFF.
- Disconnect and inspect the ABS module connector (if not previously disconnected).
- Repair:
- corrosion (install new connector or terminal - clean module pins)
- damaged or bent pins - install new terminals or pins
- pushed-out pins - install new pins as necessary
- Reconnect the ABS module connector. Make sure it 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.