Power Distribution Module: Description and Operation
POWER DISTRIBUTIONThis information 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:
- Power Distribution Center (PDC)
- Fuseblock module
- Relay and fuse block.
The power distribution system also incorporates various types of circuit control and protection features, including:
- Automatic resetting circuit breakers
- Blade-type fuses
- Cartridge fuses
- Circuit splice blocks
- Flashers
- 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. Refer to the index for the location of complete circuit diagrams for the various 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
A cigar lighter is available equipment on this model. The cigar lighter is installed in the instrument panel accessory switch plate, which is located near the center of the instrument panel, inboard of the radio. The cigar lighter base is secured by a snap fit within the instrument panel accessory switch plate.
The cigar lighter knob and heating element unit, and the cigar lighter receptacle unit are available for service. 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 receptacle 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 fuseblock module only when the ignition switch is in the Accessory or ON positions.
The 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 receptacle shell, the heating element resistor coil is grounded through its housing to the receptacle 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 receptacle shell.
Two small spring-clip retainers are located on either side of the insulated contact inside the bottom of the receptacle 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 receptacle shell, the protective heat shield slides downward on the housing so that the heating element is recessed and shielded around its circumference for safety.
CIRCUIT BREAKER
Automatic resetting circuit breakers are used to protect the power seat and power window system circuits. These circuit breakers are located in the fuse-block module, which is under the instrument panel. These circuit breakers can protect the systems from a short circuit, or from an overload condition caused by an obstructed or stuck seat adjuster or power window regulator.
The circuit breaker cannot be repaired and, if faulty or damaged, it must be replaced.
The circuit breaker contains a bi-metal strip between two contacts forming the link in the circuit. The automatic reset feature is used when the system circuit encounters an overload condition or a short to ground. An overload condition causes the bi-metal strip to heat and bend to the open position, disconnecting current flow to the circuit. Then as the system overload or short circuit is removed, the bi-metal strip cools, re-establishing contact to allow current flow to the circuit.
GENERATOR CARTRIDGE FUSE
A 140 ampere generator cartridge fuse is used on this model. The generator cartridge fuse is similar to other cartridge fuses found in the Power Distribution Center (PDC). This fuse has a color-coded plastic housing and a clear plastic fuse conductor inspection cover like other cartridge fuses, but has a higher current rating and is connected and secured with screws instead of being pushed onto male spade-type terminals. The generator cartridge fuse cannot be repaired and, if faulty or damaged, it must be replaced.
The generator cartridge fuse is secured between the two B(+) terminal stud connection bus bars within the Power Distribution Center (PDC). This fuse protects the vehicle electrical system from damage that could be caused by excessive charging system output and/or excessive electrical system current levels resulting from a faulty generator or faulty charging system control circuits. If the current rating of the fuse is exceeded, the fuse conductor melts to open the generator output circuit connection to the PDC. If a generator cartridge fuse fails, be certain to completely inspect and test the vehicle charging system before replacing the fuse and returning the vehicle to service. Refer to Charging System for the charging system diagnostic procedures. Refer to Wiring Diagrams for the location of complete PDC circuit diagrams.
Fig. 2 Fuseblock Module Location:
FUSE BLOCK
An electrical fuseblock module is concealed behind the driver side instrument panel end cap (Fig. 2), just rearward of the relay and fuse block. The fuse-block module serves to distribute electrical current to many of the accessory systems in the vehicle. The fuseblock module houses up to twenty blade-type mini fuses, up to two blade-type automatic resetting circuit breakers and an International Standards Organization (ISO) relay. Additional provisions are available in the fuseblock module for a second ISO relay and an ignition lamp time delay relay; however, these provisions are not used in this vehicle application.
The molded plastic fuseblock module housing has an integral mounting bracket that is secured with two screws to the left instrument panel end bracket. The driver side instrument panel end cap also serves as a snap-fit fuse access panel that can be removed for service of the fuseblock module and the relay and fuse block. A finger recess is molded into the end cap for easy removal. A fuse layout map is molded onto the back side of the end cap to ensure proper fuse identification.
The fuseblock module is integral to the instrument panel wire harness. If any internal circuit or the fuseblock module housing is faulty or damaged, the entire fuseblock module and instrument panel wire harness unit must be replaced.
All of the circuits entering and leaving the fuseblock module do so through the instrument panel wire harness. Internal connection of all of the fuseblock module circuits is accomplished by an intricate combination of hard wiring and bus bars.
IOD FUSE
All vehicles are equipped with an Ignition-Off Draw (IOD) fuse that is removed from its cavity within the relay and fuse block when the vehicle is shipped from the factory. Dealer personnel are to remove the IOD fuse from the storage location and install it into relay and fuse block cavity # 1 as part of the preparation procedures performed just prior to new vehicle delivery.
The driver side instrument panel end cap also serves as a snap-fit fuse access panel that can be removed to provide service access to the fuses in the relay and fuse block. A finger recess is molded into the end cap for easy removal. A fuse layout map is molded onto the instrument panel side of the end cap to ensure proper fuse identification. The IOD fuse is a 15 ampere mini blade-type fuse and, when removed, it is stored in an empty fuse holder molded into the instrument panel side of the end cap
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, including the clock. 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 removed from relay and fuse block fuse cavity # 1 when the vehicle is shipped from the assembly plant. Dealer personnel must install 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 serves no useful purpose to the dealer technician in the service or diagnosis of any vehicle system or condition, other than the same purpose as that of any other standard circuit protection device.
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. Refer to Battery for the location of additional service information covering the battery.
Fig. 5 Power Distribution Center Location:
POWER DISTRIBUTION CENTER
All of the electrical current distributed throughout this vehicle is directed through the standard equipment Power Distribution Center (PDC) (Fig. 5). The molded plastic PDC housing is located in the left front corner of the engine compartment, just inboard of the battery. The PDC houses the generator cartridge fuse and up to fourteen other maxi-type cartridge fuses, which replace all in-line fusible links. The PDC also houses up to two blade-type mini fuses, and up to seven International Standards Organization (ISO) relays (two standard-type and five micro-type).
The PDC housing is mounted on a stamped and welded metal bracket which is secured to the engine side of the radiator and headlamp support structure within the engine compartment. A tab on the lower end of the integral support brace of the PDC bracket fits into a slot in the left side of the headlamp support panel, and two screws secure a tab on the forward end of the PDC bracket to the upper radiator grille support panel. Three receptacles with snap tabs (one on the inboard side, and two on the outboard side) that are integral to the molded plastic PDC housing fit over stanchions that are integral to the PDC bracket and snap into place. The PDC housing has a molded plastic cover that includes two integral hinge tabs on the inboard side, and an integral latch on the outboard side. The PDC cover is easily opened or removed for service access and has a convenient adhesive-backed fuse and relay layout map affixed to the inside surface of the cover to ensure proper component identification.
The PDC unit cannot be repaired and is only serviced as a unit with the headlamp and dash wire harness. If the internal circuits or the PDC housing are faulty or damaged, the headlamp and dash wire harness unit must be replaced.
All of the current from the battery and the generator output enters the PDC through two cables with eyelets that are secured with nuts to the two B(+) terminal studs located just inside the rearward facing end of the PDC housing. The PDC cover is unlatched and removed to access the battery and generator output connection B( +) terminal studs, the fuses and the relays. Internal connection of all of the PDC circuits is accomplished by an intricate combination of hard wiring and bus bars. Refer to Power Distribution for the location of complete PDC circuit diagrams.
POWER OUTLET
An accessory power outlet is optional equipment on this model. The power outlet is installed in the instrument panel accessory switch plate, which is located near the center of the instrument panel, inboard of the radio. The power outlet base is secured by a snap fit within the instrument panel accessory switch plate. 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 fuseblock 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. 10 Relay And Fuse Block Location:
RELAY CENTER
An electrical relay and fuse block is concealed behind the driver side instrument panel end cap (Fig. 10), just forward of the fuseblock module. The relay and fuse block provides additional capacity for distribution and control of electrical current for the accessory systems of this vehicle, which could not be accommodated by the fuseblock module or the Power Distribution Center (PDC). The relay and fuse block has cavities for up to four additional blade-type mini fuses, the electronic combination flasher, and three additional International Standards Organization relays (one standard-type and two micro-type).
The relay and fuse block is snap fit onto mounting tabs located on the back of the left instrument panel end bracket, behind the left outboard end of the instrument panel. The driver side instrument panel end cap also serves as a snap-fit fuse access panel that can be removed for service of the relay and fuse block and the fuseblock module. A finger recess is molded into the end cap for easy removal. A fuse layout map is molded onto the back side of the end cap to ensure proper fuse identification.
The relay and fuse block unit cannot be repaired and is only serviced as a unit with the instrument panel wire harness assembly. If the relay and fuse block housing or its internal circuits are faulty or damaged, the entire relay and fuse block and instrument panel wire harness unit must be replaced.
The relay and fuse block is integral to the instrument panel wire harness, and all circuits entering or leaving this module do so through the instrument panel wire harness. Internal connection of all of the relay and fuse block circuits is accomplished by hard wiring. Refer to Fuse/Fuse Block for the location of complete circuit diagrams and cavity assignments for the relay and fuse block.