405 L4-1905cc 1.9L (1989)
Antilock Brakes / Traction Control Systems: Description and Operation
General System Description
When the ignition switch is turned to Accy or Run, the positive battery junction block provides voltage to the electro-valve assembly. Voltage is then
passed on to the electro pump assembly. Fuse F12 provides voltage to the anti-lock brake system and pressure switch.
The anti-lock brake system receives a signal from the electro valve assembly which determines how the brake pressure is distributed.
When the engine is started, the anti-lock brake system checks its input and internal circuits for proper operations. If all signals are good, it energizes the
ABS main relay, which in turn will turn off the anti-lock indicator light.
During operation the wheel sensors generate voltage signals which are input in the anti-lock brake controller. These signals have a frequency
proportional to the wheel rotation speed.
When the possibility of lock-up occurs, the appropriate inlet valve is energized, preventing further increase in brake pressure at that wheel. If the speed
sensor indicates that the wheel is continuing to lock-up, the outlet valve for that wheel is energized, reducing the pressure at the wheel. When the wheel
begins to resume normal rotation, both valves are returned to their normal condition, allowing brake pressure to be re-applied.
The anti-lock brake controller continuously processes the information it receives from each wheel sensor. If, during braking, one or more wheels begins
to lock up, the anti-lock brake controller begins the ABS processes and determines the correct sequence of operation of the inlet and outlet valves.
The indicator will light when it is grounded by the pressure switch or anti-lock brake indicator relay. The anti-lock brake indicator relay will only
energize when the electro pump assembly senses a problem and provide a ground to it. The pressure switch will provide ground when it closes because
of low hydraulic brake pressure. The brake warning indicator will also light if the parking brake in engaged.
