Power and Ground Distribution: Description and Operation
POWER DISTRIBUTIONThis group covers the various standard and optional power distribution components used on this model. The power distribution system for this vehicle consists of the following components:
- Integrated Power Module (IPM)
- Front Control Module (FCM)
- Power Distribution Center (PDC)
- Power Outlets
- Cigar Lighter Outlets
- Relays
Refer to Wiring Diagrams for complete circuit schematics.
The power distribution system also incorporates various types of circuit control and protection features, including:
- Automatic resetting circuit breakers
- Blade-type fuses
- Bus bars
- Cartridge fuses
- Circuit splice blocks
- Flashers
- Fusible links
- Relays
Following are general descriptions of the major components in the power distribution system. See the owner's manual in the vehicle glove box for more information on the features and use of all of the power distribution system components.
The power distribution system for this vehicle is designed to provide safe, reliable, and centralized distribution points for the electrical current required to operate all of the many standard and optional factory-installed electrical and electronic powertrain, chassis, safety security comfort and convenience systems. At the same time, the power distribution system was designed to provide ready access to these electrical distribution points for the vehicle technician to use when conducting diagnosis and repair of faulty circuits. The power distribution system can also prove useful for the sourcing of additional electrical circuits that may be required to provide the electrical current needed to operate many accessories that the vehicle owner may choose to have installed in the aftermarket.
CIGAR LIGHTER OUTLET
On models equipped a cigar lighter outlet is installed in the instrument panel center lower bezel, which is located near the bottom of the instrument panel center stack area, below the heater and air conditioner controls. The cigar lighter outlet is secured by a snap fit within the center lower bezel.
The cigar lighter outlet, plastic cap and the knob and heating element unit are available for service replacement. These components cannot be repaired and, if faulty or damaged, they must be replaced.
The cigar lighter consists of two major components: a knob and heating element unit, and the cigar lighter base or outlet shell. The receptacle shell is connected to ground, and an insulated contact in the bottom of the shell is connected to battery current. The cigar lighter receives battery voltage from a fuse in the junction block when the ignition switch is in the Accessory or Run positions.
The cigar lighter knob and heating element are encased within a spring-loaded housing, which also features a sliding protective heat shield. When the knob and heating element are inserted in the outlet shell, the heating element resistor coil is grounded through its housing to the outlet shell. If the cigar lighter knob is pushed inward, the heat shield slides up toward the knob exposing the heating element, and the heating element extends from the housing toward the insulated contact in the bottom of the outlet shell.
Two small spring-clip retainers are located on either side of the insulated contact inside the bottom of the outlet shell. These clips engage and hold the heating element against the insulated contact long enough for the resistor coil to heat up. When the heating element is engaged with the contact, battery current can flow through the resistor coil to ground, causing the resistor coil to heat.
When the resistor coil becomes sufficiently heated, excess heat radiates from the heating element causing the spring-clips to expand. Once the spring-clips expand far enough to release the heating element, the spring-loaded housing forces the knob and heating element to pop back outward to their relaxed position. When the cigar lighter knob and element are pulled out of the outlet shell, the protective heat shield slides downward on the housing so that the heating element is recessed and shielded around its circumference for safety.
Fig. 1 DR Integrated Power Module:
INTEGRATED POWER MODULE
The Integrated Power Module (IPM) is a combination of the Power Distribution Center (PDC) and the Front Control Module (FCM). The IPM is located in the engine compartment, next to the battery on this model. The power distribution center mates directly with the Front Control Module (FCM) to form the Integrated Power Module Fuse and Relay Center. The Power Distribution Center (PDC) is a printed circuit board based module that contains fuses and relays, while the front control module contains the electronics controlling the integrated power module and other functions. This Integrated Power Module connects directly to the battery positive via a stud located on top of the unit. The ground connection is via electrical connectors. The Integrated Power Module provides the primary means of voltage distribution and protection for the entire vehicle.
The molded plastic integrated power module housing includes a base and cover. The Integrated Power Module cover is easily opened or removed for service access by unscrewing the cover retaining nut and has a fuse and relay layout map integral to the inside surface of the cover. This integrated power module housing base and cover are secured in place via bolts to the left front fender support assembly
Replaceable components of the integrated power module assembly are broken down into the following components: the Power Distribution Center (PDC) (without fuses or relays), the integrated power module cover, the Front Control Module (FCM) and the Integrated Power Module Assembly which includes the power distribution center, the cover and FCM.
Refer to the Front Control Module in the Electronic Control Module for information on the front control module.
All of the current from the battery and the generator output enters the integrated power module via a stud on the top of the module. The integrated power module cover is removed to access the fuses or relays. Internal connections of all of the power distribution center circuits is accomplished by a combination of bus bars and a printed circuit board. Refer to the Wiring section for complete integrated power module circuit schematics.
IOD FUSE
All vehicles are equipped with an Ignition-Off Draw (IOD) fuse that is disconnected within the Integrated Power Module when the vehicle is shipped from the factory. Dealer personnel are to reconnect the IOD fuse in the Integrated Power Module as part of the preparation procedures performed just prior to new vehicle delivery.
Fig. 6 IOD Fuse Location:
A laser printed fuse layout map is integral to the Integrated Power Module cover to ensure proper fuse identification. The IOD fuse is a 20 ampere mini blade-type fuse, located in fuse cavity # 51 (Fig. 6).
The fuse is secured within a black molded plastic fuse holder and puller unit that serves both as a tool for disconnecting and reconnecting the fuse in its Integrated Power Module cavity, and as a fuse holder that conveniently stores the fuse in the same Integrated Power Module cavity after it has been disconnected.
Circuits Included With IOD Fuse
- Cluster (CCN)
- Diagnostic Connector
- Map Lamps
- Glove Box Lamp
- Courtesy Lamps
- Radio
- Underhood Lamp
The term ignition-off draw identifies a normal condition where power is being drained from the battery with the ignition switch in the OFF position. The IOD fuse feeds the memory and sleep mode functions for some of the electronic modules in the vehicle as well as various other accessories that require battery current when the ignition switch is in the OFF position. The only reason the IOD fuse is disconnected is to reduce the normal IOD of the vehicle electrical system during new vehicle transportation and pre-delivery storage to reduce battery depletion, while still allowing vehicle operation so that the vehicle can be loaded, unloaded and moved as needed by both vehicle transportation company and dealer personnel.
The IOD fuse is disconnected from Integrated Power Module fuse cavity # 51 when the vehicle is shipped from the assembly plant. Dealer personnel must reconnect the IOD fuse when the vehicle is being prepared for delivery in order to restore full electrical system operation. Once the vehicle is prepared for delivery, the IOD function of this fuse becomes transparent and the fuse that has been assigned the IOD designation becomes only another Fused B(+) circuit fuse.
The IOD fuse can be used by the vehicle owner as a convenient means of reducing battery depletion when a vehicle is to be stored for periods not to exceed about thirty days. However, it must be remembered that disconnecting the IOD fuse will not eliminate IOD, but only reduce this normal condition. If a vehicle will be stored for more than about thirty days, the battery negative cable should be disconnected to eliminate normal IOD; and, the battery should be tested and recharged at regular intervals during the vehicle storage period to prevent the battery from becoming discharged or damaged.
POWER OUTLET
Two power outlets are utilized on this model. One in the instrument panel next to the cigar lighter and the other in the center console. The power outlet bases are secured by a snap fit within the instrument panel or trim panel. A plastic protective cap snaps into the power outlet base when the power outlet is not being used, and hangs from the power outlet base mount by an integral bail strap while the power outlet is in use.
The power outlet receptacle unit and the accessory power outlet protective cap are available for service. The power outlet receptacle cannot be repaired and, if faulty or damaged, it must be replaced.
The power outlet base or receptacle shell is connected to ground, and an insulated contact in the bottom of the shell is connected to battery current. The power outlet receives battery voltage from a fuse in the integrated power module at all times.
While the power outlet is very similar to a cigar lighter base unit, it does not include the two small spring-clip retainers inside the bottom of the receptacle shell that are used to secure the cigar lighter heating element to the insulated contact.
Fig. 8 ISO Relay:
RELAY
A relay (Fig. 8) is an electromechanical device that switches fused battery current to a electrical component when the ignition switch is turned to the Accessory or Run positions, or when controlled by a electronic module. The relays are located in the integrated power module.
The relay is a International Standards Organization (ISO) relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions.
A relay cannot be repaired or adjusted and, if faulty or damaged, it must be replaced.
The ISO relay consists of an electromagnetic coil, a resistor and three (two fixed and one movable) electrical contacts. The movable (common feed) relay contact is held against one of the fixed contacts (normally closed) by spring pressure. When the electromagnetic coil is energized, it draws the movable contact away from the normally closed fixed contact, and holds it against the other (normally open) fixed contact.
When the electromagnetic coil is de-energized, spring pressure returns the movable contact to the normally closed position. The resistor is connected in parallel with the electromagnetic coil in the relay, and helps to dissipate voltage spikes that are produced when the coil is de-energized.
Fig. 9 DR ISO Micro Relay:
MICRO RELAY
A micro-relay is a conventional International Standards Organization (ISO) micro relay (Fig. 9). Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The relay is contained within a small, rectangular, molded plastic housing and is connected to all of the required inputs and outputs by five integral male spade-type terminals that extend from the bottom of the relay base.
Relays cannot be adjusted or repaired and, if faulty or damaged, the unit must be replaced.
A micro-relay is an electromechanical switch that uses a low current input from one source to control a high current output to another device. The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. A resistor is connected in parallel with the relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.