Pinpoint Test G: DTC C1187 - Brake Fluid Level Input Circuit Open

Refer to appropriate SYSTEM WIRING DIAGRAMS article, Vehicle Dynamic Systems for schematic and connector information.

Normal Operation 

The brake fluid level switch is a normally open switch attached to a flotation device in the master cylinder reservoir. The ABS module sends out a voltage along circuit CMC19 (GY/VT) which returns to the module along circuit RCM19 (YE/GY). When the brake fluid is at the correct level, the switch remains open and the ABS module detects a returning voltage. When the fluid level falls below a predetermined level, the switch closes and connects circuit CMC19 (GY/VT) and circuit RCM19 (YE/GY) to ground circuit GD121 (BK/YE). The ABS module will no longer detect the returning voltage and sends a signal to the instrument cluster along circuit CCA02 (GN/VT) and the instrument cluster illuminates the red brake warning indicator.

• DTC C1187 Brake Fluid Level Input Circuit Open - If, during normal operation or the ABS module on-demand self test, the ABS module detects and open circuit or a short to ground on circuit CMC19 (GY/VT) or RMC19 (YE/GY), DTC C1187 will be set.

This pinpoint test is intended to diagnose the following:

• Wiring, terminals or connectors
• Brake fluid level switch (integral to the brake fluid reservoir)
• ABS module

PINPOINT TEST G: DTC C1187 - BRAKE FLUID LEVEL INPUT CIRCUIT OPEN 

1. G1 ISOLATE THE BRAKE FLUID LEVEL SWITCH 
   • Disconnect: Brake Fluid Level Switch C124
   Fig 1: Connecting Fused Jumper Wire
   Courtesy of FORD MOTOR CO.
   • Connect a fused (5A) jumper wire between brake fluid level switch C124-2, circuit CMC19 (GY/VT), harness side and brake fluid level switch C124-3, circuit RCM19 (YE/GY), harness side.
   • Connect the diagnostic tool.
   • Key in ON position.
   • Using the scan tool, clear the DTCs and repeat the self-test with the brake pedal not applied. Retrieve the DTCs.
   • Is DTC C1187 retrieved again? 
   1. YES  : Go to  G2.
   2. NO  : INSTALL a new brake master cylinder. REFER to BRAKE SYSTEM - GENERAL INFORMATION article. CLEAR the DTCs and REPEAT the self-test with the brake pedal not applied.
2. G2 CHECK CIRCUITS CMC19 (GY/VT) AND RMC19 (YE/GY) FOR AN OPEN 
   • Key in OFF position.
   • Disconnect: ABS Module C135
   Fig 2: Measuring Resistance
   Courtesy of FORD MOTOR CO.
   • Measure the resistance between:
     • ABS module C135-25, circuit CMC19 (GY/VT), harness side and brake fluid level switch C124-2, circuit CMC19 (GY/VT), harness side.
     • ABS module C135-23, circuit RCM19 (YE/GY), harness side and brake fluid level switch C124-3, circuit RCM19 (YE/GY), harness side.
   • Are the resistances less than 5 ohms? 
   1. YES  : Go to  G3.
   2. NO  : REPAIR the affected circuit(s). CLEAR the DTCs. REPEAT the self-test with the brake pedal not applied.
3. G3 CHECK CIRCUITS CMC19 (GY/VT) AND RCM19 (YE/GY) FOR A SHORT TO GROUND 
   Fig 3: Measuring Resistance
   Courtesy of FORD MOTOR CO.
   • Measure the resistance between ground and:
     • brake fluid level switch C124-2, circuit CMC19 (GY/VT), harness side.
     • brake fluid level switch C124-3, circuit RCM19 (YE/GY), harness side.
   • Is the resistance greater than 10,000 ohms? 
   1. YES  : Go to  G4.
   2. NO  : REPAIR the affected circuit(s). CLEAR the DTCs. REPEAT the self-test with the brake pedal not applied.
4. G4 CHECK FOR CORRECT ABS MODULE OPERATION 
   • Check ABS module C135 for:
     • corrosion.
     • pushed-out pins.
     • spread terminals.
   • Connect: ABS Module C135
   • Make sure the connector seats correctly, then operate the system and verify the concern is still present.
   • Is the concern still present? 
   1. YES  : INSTALL a new ABS module. REFER to Anti-Lock Brake System (ABS) Module . TEST the system for normal operation.
   2. NO  : The system is operating correctly at this time. Concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test with the brake pedal not applied.