HOOD AJAR SWITCH
DESCRIPTION
The hood ajar switch is a normally closed, single pole, spring-loaded plunger actuated switch. This switch has two unique versions that are used in two different applications. One switch is used only on vehicles equipped with the Vehicle Theft Security System (VTSS) for sale in certain export markets where protection of the underhood area is required equipment. The second switch is used only on domestic vehicles equipped with an optional remote starter system.
The molded plastic switch body (5) has an integral molded connector receptacle (1) on the lower end containing two terminal pins. The switch is connected to the vehicle electrical system through a dedicated take out of the headlamp and dash wire harness. Two integral latches (2) lock the switch into a keyed mounting hole in the stamped steel switch mounting bracket. The mounting bracket is secured with screws to the left inner fender shield near the fender ledge in the engine compartment. The underside of the hood panel inner reinforcement actuates the switch plunger as the hood panel is closed.
The switch plunger (3) extends through a mounting collar (4) and a sleeve-like retainer ring on the upper end of the switch body. The retainer ring has a one time, self-adjustment feature that is activated after the switch is installed by closing the hood. The retainer ring is also color-coded to aid in identifying the switch application. A dark brown retainer ring identifies the underhood security switch application, while a white retainer ring identifies the remote starter system application.
An installed hood ajar switch cannot be readjusted or repaired. If the switch is damaged, ineffective, or requires readjustment, it must be replaced with a new unit.
OPERATION
The hood ajar switches are interchangeable physically, but not functionally. In each case, the hood ajar switch is a normally closed switch that is held open as the spring-loaded switch plunger is depressed by the inner hood panel reinforcement when the hood panel is closed and latched. When the hood is opened, the spring-loaded switch plunger extends from the switch body and the switch contacts are closed.
In the underhood security application (export vehicles only - dark brown retainer ring), the switch is connected in series between ground and the hood ajar switch sense input of the Front Control Module (FCM). The FCM uses an internal resistor pull up to monitor the state of the hood ajar switch contacts.
In the remote starter system application (domestic vehicles only - white retainer ring) the switch has a 1 kilohm diagnostic resistor connected in parallel to the switch contacts between the two switch terminals. The switch is connected in series between an output of the FCM and the hood ajar switch sense input of the FCM. The FCM continually monitors this circuit and will store a Diagnostic Trouble Code (DTC) for any fault that it detects.
The components of the switch self-adjustment feature include an integral stop on the shaft of the plunger and a ribbed, ratcheting sleeve-like retainer ring at the top of the switch body from which the plunger extends. With the switch mounting collar secured in its mounting bracket, the plunger is depressed by the hood inner reinforcement as the hood is closed. As the plunger is depressed, the plunger stop contacts the top of the retainer ring and it is driven downward, ratcheting through the switch mounting collar until the hood is fully closed and latched. The ribs on the retainer ring are engaged within the mounting collar to maintain this adjusted position.
The hood ajar switch as well as the hard wired circuits between the switch and the FCM may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the electronic controls or communication between modules and other devices related to hood ajar switch operation that provide some features of the export vehicle theft or domestic remote starter systems. The most reliable, efficient, and accurate means to diagnose the electronic controls and communication related to hood ajar switch operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.