1, 2 and 3 Digit Codes: 14

Fault Code 14 Diagnosis Chart:

Hydraulic Assembly Plausibility Switches Circuit:

TRAVEL SWITCHES OPERATION
Two piston travel switches are located in the booster reed block assembly. They are monitored on ABCM pin 31, which is provided 5 volts by the ABCM. When the brakes are not applied, this line is held to ground by the piston travel switches as in the above schematic.

When the brakes are partially applied, switch S2A opens. Due to internal resistance in the reed block, ABCM pin 31 is then held at 2.5 volts (S2A open and S2B closed).

When the brake pedal approaches full stroke, switch S2B opens. With both S2A and S2B open, a path to ground no longer exists for circuit PT1 and ABCM pin 31 is forced to 5 volts. The ABCM monitors voltage on pin 31 to determine status of the piston travel switches.

SWITCH SEQUENCE
When normal brake application is made, the following sequence of events should take place:
1. As soon as the pedal is depressed, the brake light switch should close, providing a 12 volt signal to ABCM pin 25.
2. As the booster piston continues to move, switch S2A opens, forcing ABCM pin 31 to 2.5 volts.
3. As the brake is applied further, the control pressure switch (S1) opens, holding ABCM pin 16 at 5 volts.
4. As full pedal travel is reached, switch S2B opens forcing ABCM pin 31 to 5 volts.

FAILURE CONDITIONS
ABCM Codes 13, 14, and 15 will set if an improper switch sequence is detected. The specific conditions required to set each code are as follows:

Code 13 - S2B opens before S1.
Code 14 - S1 opens before S2A.
Code 15 - S1 or S2B opens before Brake Light Switch closes.

Air in the brake system will sometimes cause Fault Codes 13, 14 or 15 to set due to additional booster piston travel requirements.