Self-Diagnostic System

The Anti-Lock Brake System/Traction Control Control Module (ABS/TCCM) is integrated with the hydraulic control unit. The hydraulic control unit contains the solenoids, input and return valves. There is not electrical connection between ABS/TCCM and hydraulic control unit. The ABS/TCCM constantly monitors the brake system by passing self-checking electrical pulses around the circuit. The following items are checked during self-check:

• Operating voltage must be approximately 9-19 volts. If voltage is not within specification, ABS/TCCM will shut down.
• Pump is monitored for voltage supply and voltage feedback.
• Monitoring for a disturbance. A failure may be caused by external radio frequency interference, internal leakage current, defective valve resistor or faulty valve.
• Internal controller failure. This would be detected by a RAM and ROM test.
• Controller Area Network (CAN) failure. ABS/TCCM checks for correct operation of CAN and performs a RAM self-check.

Signals processed by the ABS/TCCM may be shared via CAN to be used for instrument cluster speed display, cruise control and ASC/TC operation. Depending on fault detected, the system will adopt one of the following operational modes:

1. ASC/TC Switches Off
   
   The ASC and TC systems will shut down until fault is corrected. ABS will continue to function normally.
2. System Inhibited
   
   Operation of the modulator assembly solenoid valve will be inhibited while fault is present. Brake system will operate as a normal brake system.
3. System Switches Off
   
   ABS or ABS/TC system will be shut-off until fault is corrected. Brake system will operate as a normal brake system.