1, 2 and 3 Digit Codes: 15

Fault Code 15 Diagnosis Chart:

Hydraulic Assembly Plausibility Switches Circuit:

LIGHT SWITCH OPERATION
The brake light switch, located on the brake pedal bracket, is normally open. When the brake pedal is applied, the switch closes and provides a 12 volt signal to ABCM pin 25.

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.