Modulator Circuit

NAME OF CODE:
Modulator Circuit

WHEN MONITORED:
During the drive-off cycle, or five seconds after key on and anytime thereafter until the next ignition reset. The valves are tested about every half second while in antilock mode and every 4 seconds in normal driving mode.

SET CONDITION:
The modulator is a group of four solenoid valves controlled by the Controller, Anti-lock Brake (CAB) to modulate brake pressure during Anti-lock Brake System (ABS) control. There are four build/decay valves, one for each wheel. During normal braking (non-ABS control), the solenoids are functionally invisible to the brake system. Modulator power comes from the solenoid drivers in the CAB and is activated by command of the CAB for ABS control. The solenoid drivers are powered through the system relay when energized. In this way, ABS can be disabled by de-energizing the system relay.

Upon detection, the ABS warning lamp is illuminated and the Modulator Circuit trouble code is set. ABS function is disabled and the lamp is illuminated until the next ignition reset.

POSSIBLE CAUSES:
- LF decay solenoid control circuit open, shorted to ground, or shorted to B(+)
- RF decay solenoid control circuit open, shorted to ground, or shorted to B(+)
- LR decay solenoid control circuit open, shorted to ground, or shorted to B(+)
- RR decay solenoid control circuit open, shorted to ground, or shorted to B(+)
- Open or short in any of the four decay solenoids
- CAB failed
- Wiring harness connector terminals spread or pushed out