Power and Ground Distribution: Description and Operation
POWER DISTRIBUTIONThe 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:
- Power Distribution Center (PDC)
- Junction Block (JB)
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.
Fig.1 Cigar Lighter And Power Outlet:
CIGAR LIGHTER OUTLET
A cigar lighter is standard equipment on this model (Fig. 1). The cigar lighter is installed in the instrument panel lower bezel, which is located near the center of the instrument panel, below the radio. The cigar lighter base is secured by a snap fit within the instrument panel lower bezel.
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 junction block 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 in the junction block are used to protect the power seat and power window system circuits. These circuit breakers can protect the systems from a short circuit, or overload condition caused by an obstructed or stuck seat adjuster, window glass or regulator.
The circuit breaker cannot be repaired and, if faulty or damaged, it must be replaced.
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 charging system diagnostic procedures.
Fig.3 Ignition-Off Draw Fuse - Typical:
IOD FUSE
All vehicles are equipped with an Ignition-Off Draw (IOD) fuse (Fig. 3) 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 for the location of additional service information covering the battery.
Fig.5 Junction Block Location:
JUNCTION BLOCK
An electrical Junction Block (JB) is concealed behind the left outboard end of the instrument panel cover (Fig. 5). 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 bladetype 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.
Fig.8 Power Distribution Center Location - Typical:
POWER DISTRIBUTION CENTER
All of the electrical current distributed throughout this vehicle is directed through the standard equipment Power Distribution Center (PDC) (Fig. 8). 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 one cable with eyelets that are secured with a nut to the one B(+) terminal stud 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 inline connector. Internal connection of all of the PDC circuits is accomplished by an intricate combination of hard wiring and bus bars.
POWER OUTLET
An accessory power outlet is optional equipment on this model The power outlet is installed in the instrument panel lower bezel, which is located near the center of the instrument panel, below the radio. The power outlet base is secured by a snap fit within the instrument panel lower bezel. 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 Power Distribution Center (PDC) 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.11 ISO Relay:
RELAY
A relay 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 junction block or power distribution center (Fig. 11).
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.12 ISO Micro Relay:
MICRO-RELAY
A micro-relay is a conventional International Standards Organization (ISO) micro relay (Fig. 12). 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.