Power and Ground Distribution: Description and Operation
POWER DISTRIBUTION SYSTEMThis covers the various standard arid optional power distribution components used on this model. The power distribution system for this vehicle consists of the following components:
- Power Distribution Center (PDC)
- Junction Block (JB)
- 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.
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.
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). The molded plastic PDC housing is located in the left front corner of the engine compartment, just behind the battery The PDC houses the generator cartridge fuse and up to ten maxi-type cartridge fuses, which replace all in-line fusible links. The PDC also houses up to seven blade-type mini fuses, up to thirteen International Standards Organization (ISO) relays (one standard-type and twelve micro-type), two joint connectors (one sixteen-way and one twenty-six-way) and a sixteen-way engine wire harness in-line connector.
The PDC housing is secured in the engine compartment at three points. Integral mounts on the front and inboard sides of the PDC housing engage and latch to stanchions that are integral to the molded plastic battery tray. An integral bracket on the rear of the PDC housing is secured with a screw to the top of the left front inner wheel house. The PDC housing has a molded plastic cover that includes two integral latches, one on each side. The PDC cover is easily opened and removed for service access and has a convenient fuse and relay layout map integral 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 inboard side of the PDC housing. The PDC cover is unlatched and removed to access the battery and generator output connection B(+) terminal studs, the fuses, the relays, the joint connectors and the engine wire harness online connector. Internal connection of all of the PDC circuits is accomplished by an intricate combination of hard wiring and bus bars.
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 falls, 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 diagnostic procedures.
Junction Block Location:
JUNCTION BLOCK
An electrical Junction Block (JB) is concealed behind the left outboard end of the instrument panel cover. The JB serves to simplify and centralize numerous electrical components, and to distribute electrical current to many of the accessory systems in the vehicle. It also eliminates the need for numerous splice connections and serves in place of a bulkhead connector between many of the engine compartment, instrument panel, and body wire harnesses. The JB houses up to nineteen blade-type fuses (two standard-type and seventeen mini-type), up to two blade- type automatic resetting circuit breakers, and two International Standards Organization (ISO) relays (one standard-type and one micro-type).
The molded plastic JB housing has integral mounting brackets that are secured with two screws to the left instrument panel end bracket. The left end of the instrument panel cover has a snap-fit fuse access panel that can be removed for service of the JB. A fuse puller and spare fuse holders are located on the back of the fuse access cover, as well as an adhesive- backed fuse layout map to ensure proper fuse identification.
The JB unit cannot be repaired and is only serviced as an assembly. If any internal circuit or the JB housing is faulty or damaged, the entire JB unit must be replaced.
All of the circuits entering and leaving the JB do so through up to nine wire harness connectors, which are connected to the JB through integral connector receptacles molded into the JB housing. Internal connection of all of the JB circuits is accomplished by an intricate combination of hard wiring and bus bars.
Ignition-Off Draw Fuse - Typical:
IGNITION-OFF DRAW FUSE
All vehicles are equipped with an Ignition-Off Draw (IOD) fuse that is disconnected within the Junction Block (JB) when the vehicle is shipped from the factory. Dealer personnel are to reconnect the IOD fuse in the JB as part of the preparation procedures performed just prior to new vehicle delivery.
The left end of the instrument panel cover has a snap-fit fuse access panel that can be removed to provide service access to the fuses in the JB. A finger recess is molded into the access panel for easy removal. An adhesive-backed fuse layout map is secured to the instrument panel side of the access panel to ensure proper fuse identification. The IOD fuse is a 15 ampere mini blade-type fuse. 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 JB cavity, and as a fuse holder that conveniently stores the fuse in the same JB cavity after it has been disconnected.
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 disconnected from JB fuse cavity 12 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 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.
Relay and Fuse Block Location:
RELAY AND FUSE BLOCK
The relay and fuse block is snap fit onto mounting tabs located on the end of the Junction Block (JB) nearest to the dash panel, under the left outboard end of the instrument panel. The relay and fuse block provides additional capacity for distribution and control of electrical current for some of the accessory systems that are unique to this vehicle, and which could not be accommodated by the JB 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 components are accessed for service by removing the steering column opening cover from the instrument panel. The relay and fuse block is then disengaged from the JB mounting tabs and pulled out from under the instrument panel. Service replacement of the relay and fuse block unit requires instrument panel assembly removal.
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 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.