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)
- 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
- Maxi fuse-type 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. Refer to the index for the location of complete circuit diagrams for the various power distribution system components.
NOTE: This information covers both Left-Hand Drive (LHD) and Right-Hand Drive (RHD) versions of this model. Whenever required and feasible, the RHO versions of affected vehicle components have been constructed as mirror-image of the LHD versions. While most of the illustrations represent only the LHD version, the diagnostic and service procedures outlined can generally be applied to either version. Exceptions to this rule have been clearly identified as LHD or RHD, if a special illustration or procedure is required.
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.
NOTE: DO NOT ATTEMPT TO SWAP POWER DISTRIBUTION CENTERS (PDC) FROM ONE VEHICLE TO ANOTHER. MOST OF THESE ASSEMBLIES ARE VEHICLE FEATURE SPECIFIC AND THEREFORE NOT INTERCHANGEABLE. ALWAYS USE THE CORRECT PART NUMBERED ASSEMBLY WHEN DIAGNOSING OR REPLACING A PDC.
CIGAR LIGHTER ELEMENT
A cigar lighter is standard equipment on this model. The cigar lighter is installed in the instrument panel accessory switch bezel, which is located near the bottom of the instrument panel center bezel area, below the heater and air conditioner controls. The cigar lighter base is secured by a snap fit within the accessory switch bezel.
The cigar lighter receptacle is serviced only as a part of the accessory switch bezel unit. If the cigar lighter base is faulty or damaged, the accessory switch bezel unit must be replaced. The cigar lighter knob and heating element unit is available for service. This component cannot be repaired and, if faulty or damaged, it 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 through the cigar lighter relay only when the ignition switch is in the Accessory or ON positions. Refer to Cigar Lighter Relay in the Description and Operation for more information on this component.
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 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.
CIGAR LIGHTER RELAY
The cigar lighter relay is an electromechanical device that switches fused battery current to the cigar lighter when the ignition switch is turned to the Accessory or ON positions. The cigar lighter relay is located in the junction block, on the right cowl side panel below the instrument panel in the passenger compartment.
The cigar lighter 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.
The cigar lighter 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 or diode, 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 or diode 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.
CIRCUIT BREAKER
A circuit breaker is used to protect a powered component (i.e..power windows, seats,....) system circuit. The automatic resetting circuit breaker can protect the system from a short circuit, or from an overload condition caused by an obstructed or stuck powered component.
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.
Fig.3 Ignition-Off Draw Fuse:
IOD FUSE
All vehicles are equipped with an Ignition-Off Draw (IOD) fuse (Fig. 3) that is removed from its cavity in the Power Distribution Center (PDC) when the vehicle is shipped from the factory. Dealer personnel are to remove the IOD fuse from the storage location and install it into .PDC fuse cavity 16 as part of the preparation procedures performed just prior to new vehicle delivery.
The PDC has a molded plastic cover that can be removed to provide service access to all of the fuses and relays in the PDC. An integral latch and hinge tabs are molded into the PDC cover for easy removal. A fuse layout map is integral to the underside of the PDC cover to ensure proper fuse and relay identification. The IOD fuse is a 15 ampere mini blade-type fuse and, when removed, it is stored in a plastic fuse holder formation that is molded into the underside of the PDC cover.
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 many 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 removed 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 PDC fuse cavity 16 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 removing 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.4 Junction Block Location:
JUNCTION BLOCK
An electrical Junction Block (JB) is concealed behind the right cowl side inner trim panel in the passenger compartment of the vehicle (Fig. 4). The JB combines the functions previously provided by a separate fuseblock module and relay center. The JB serves to simplify and centralize numerous electrical components, as well as 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 twenty-seven blade-type fuses (three standard- type and twenty-four mini-type), up to three blade-type automatic resetting circuit breakers, and four International Standards Organization (ISO) relays (three standard4ype and one micro-type).
The molded plastic JB housing has integral mounting brackets that are secured with three nuts to studs on the right cowl side inner panel below the instrument panel. The right cowl side inner trim panel is secured to a stud on the JB with a push nut. A snap-fit fuse access panel can be removed for service of the JB fuses and also conceals the push nut A finger recess is molded into the front of the fuse access panel for easy removal, and a fuse puller and spare fuse holders are located on the back of the fuse access panel.
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 ten 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. Refer to Junction Block for the location of complete JB circuit diagrams.
Fig.7 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. 7). The molded plastic PDC housing is located on the right side of the engine compartment, just behind the battery. The PDC houses up to fourteen blade-type maxi fuses, which replace all in-line fusible links. The PDC also houses up to twelve blade-type mini fuses, and up to eight International Standards Organization (ISO) relays (four standard-type and four micro-type).
The PDC housing is secured to a stamped sheet metal bracket in the engine compartment by mounting slots and tabs that are integral to the PDC housing. The PDC mounting bracket is secured with two screws to the right front inner fender shield above the right front wheel house. 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 fuse and relay layout map integral to the inside surface of the cover to ensure proper component identification. A separate molded plastic B(+) terminal stud cover is secured by two integral tabs and a latch to one end of the PDC housing.
The PDC cover, the PDC housing lower cover, the PDC B(+) terminal stud cover, the PDC relay wedges and the PDC relay cassettes are available for service replacement. The PDC main housing unit, the fuse wedges, the fuse cassette and the bus bars cannot be repaired and are only serviced as a unit with the headlamp and dash wire harness. If the PDC main housing unit, fuse wedges, fuse cassette or the bus bars 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 and eyelets that are secured with a nut to the PDC B(+) terminal stud located on one end of the PDC housing. The PDC B(+) terminal stud cover is unlatched and removed to access the battery and generator output connection B(+) terminal stud. The PDC cover is unlatched and opened or removed to access the fuses or 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 standard equipment on this model. The power outlet is installed in the instrument panel accessory switch bezel, which is located near the bottom of the instrument panel center bezel area, below the heater and air conditioner controls. The power outlet base is secured by a snap fit within the accessory switch 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 serviced only as a part of the accessory switch bezel unit. If the power outlet base is faulty or damaged, the entire accessory switch bezel unit 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 junction block 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.