Hood Ajar Switch (Single) Explanation

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 STOP/START system for sale in certain export markets where protection of the under hood 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 (Fig 1) #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 engine compartment 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 a screw to the forward end of the left load beam in the left front corner of 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 under hood STOP/START 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.

HOOD AJAR SWITCH 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 striker cap on 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 under hood stop/start and security system applications (export vehicles only - dark brown retainer ring), the switch is connected in series between ground and the hood ajar switch sense input of the Totally Integrated Power Module (TIPM). The TIPM 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 TIPM and the hood ajar switch sense input of the TIPM. The TIPM 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, 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 striker cap on 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 and ratchets 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 TIPM 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 and 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.

HOOD AJAR SWITCH, SINGLE REMOVAL
1. Open the hood.
2. Disconnect and isolate the negative cable from the battery.
3. Disconnect the IBS/negative battery cable assembly from the negative battery post.
4. From the top of the mounting bracket (Fig 4) #3 in the left front corner of the engine compartment, squeeze the two remote start hood ajar switch latch tabs #1 together and pull the switch upward.
5. Pull the remote start hood ajar switch up through the hole in the mounting bracket (Fig 4) #3 far enough to access and disconnect the harness connector #2 from the switch connector receptacle.
6. Remove the remote start hood ajar switch from the engine compartment.

HOOD AJAR SWITCH, SINGLE INSTALLATION
1. Position the remote start hood ajar switch near the hole in the mounting bracket (Fig 2) #3 on the front of the left load beam in the left front corner of the engine compartment.
2. Route the harness connector (Fig 2) #2 through the switch mounting bracket #3 and connect it to the switch connector receptacle.
3. From the top of the mounting bracket, press the switch downward into the mounting hole until the integral switch latch tabs lock it into place.
4. If equipped with IBS, connect the IBS/negative battery cable assembly to the negative battery post.
5. Reconnect the negative cable to the battery.
6. Close and latch the hood.

HOOD AJAR SWITCH BRACKET, SINGLE REMOVAL
1. Disconnect and isolate the negative cable or the Intelligent Battery Sensor (IBS) and negative cable assembly (as equipped) from the negative terminal post of the battery.
2. Remove the remote start hood ajar switch (Fig 2) #1 from the mounting bracket. Refer to SWITCH, HOOD AJAR, REMOVAL.
3. Remove the screw (Fig 3) #1 that secures the remote start hood ajar switch bracket #2 to the front of the left front load beam in the engine compartment.
4. Remove the hood ajar switch bracket (Fig 3) #2 from the load beam.

HOOD AJAR SWITCH BRACKET, SINGLE INSTALLATION
1. Position the remote start hood ajar switch bracket (Fig 3) #2 to the left front load beam in the engine compartment.
2. Install and tighten the screw (Fig 3) #1 that secures the bracket to the load beam. Tighten the screw to 8 N.m (71 in. lbs.).
3. Reinstall the remote start hood ajar switch (Fig 4) #1 into the mounting bracket. Refer to SWITCH, HOOD AJAR, INSTALLATION.
4. Reconnect the negative cable to the battery.