System Description

When ignition is turned on, control module activates warning indicators on instrument panel and performs an initial diagnostic test which ensures there are no internal faults in control module. At same time, main relay in combination relay is activated so hydraulic modulator valves are supplied with power. See Figure . Control module then checks operation of valves by activating them in sequence.

If no fault is detected, warning indicators go out about 2 seconds after engine is started. When vehicle is driven, control module checks that it is receiving signals from wheel sensors. At 20 MPH, it checks that hydraulic pump is operating by activating pump relay so pump is started. This is confirmed by a signal from rotation sensor. In addition to the initial diagnostic tests, control module continuously checks that all signals and components are operating, and there are no internal faults in control module.