Description And Operation: Plunger
The hood ajar switch is a normally closed, single pole, spring-loaded plunger actuated switch. This switch has two unique applications. One application is on vehicles equipped with the Vehicle Theft Alarm (VTA) for sale in certain export markets where protection of the under hood area is required. The second application is for domestic vehicles equipped with an optional remote start 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 right end of the upper cross member of the Front End Module (FEM) carrier near the right 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 export VTA switch application also has a molded plastic switch striker cap secured by a blind rivet to the hood panel inner reinforcement to provide additional resistance to unauthorized switch tampering.
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.
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.
The plunger of the optional stand alone hood ajar switch is actuated by a molded plastic striker secured to the underside of the hood panel inner reinforcement as the hood panel is closed. When the hood is closed and properly latched, the hood ajar switch is an open circuit. When the hood is open or only partially latched, the hood ajar switch is a closed circuit. The switch has a 1 kilohm diagnostic resistor connected in parallel to the switch contacts located between the two switch terminals. The stand alone hood ajar switch is hard wired in series between a return circuit and a signal circuit of the Powertrain Control Module (PCM) (also known as the Engine Control Module/ECM).
The PCM reads the hard wired hood ajar switch input through an internal pull-up resistor, then uses this input to control certain features of the start-stop system. The PCM may also send electronic hood ajar switch status messages to other electronic modules in the vehicle over the CAN data bus.
The stand alone hood ajar switch as well as the hard wired inputs and outputs of the switch may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information.