DESCRIPTION
This 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 correct article: SYSTEM WIRING DIAGRAMS - R1500 SYSTEM WIRING DIAGRAMS - R2500 or SYSTEM WIRING DIAGRAMS - R3500 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
- Cartridge fuses
- 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.
OPERATION
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.
Scheme 351
On models equipped a cigar lighter outlet is installed to the left of the center stack area in the lower instrument panel. The cigar lighter outlet is secured by a snap fit within the 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.
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 correct article: SYSTEM WIRING DIAGRAMS - R1500 SYSTEM WIRING DIAGRAMS - R2500 or SYSTEM WIRING DIAGRAMS - R3500 . for complete integrated power module circuit schematics.
Scheme 352
Scheme 353
- Disconnect the negative and positive battery cables.
- Unsnap cover and remove the B+ terminal nut from the integrated power module B+ terminal. Remove the B+ cable from the integrated power module.
- Disconnect the gray connector from the integrated power module.
- Remove the integrated power module retaining bolt and screw (Scheme 352)
- Grasp the integrated power module with two hands and slide the assembly in the direction shown (Scheme 353) to free the module from its mounting bracket. Position the assembly upside down to access the electrical connectors located on the bottom of the unit.
- Disconnect the electrical connectors by depressing the locking tab and rotating the connector arm outboard, until the connector is free from the module assembly. Be certain to pull the connectors straight off.
- Position the integrated power module on a bench and remove the four front control module retaining screws.
- Disconnect the front control module by pulling it straight off the integrated power module.
Scheme 354
- Connect the front control module by pushing it straight on the integrated power module electrical receptacle.
- Install the four front control module retaining screws. Torque to 30 in. lbs. +/-5. NOTE: Integrated power module electrical connectors are color coded to ease location reference (Scheme 354)
- Connect the electrical connectors by pushing straight on and rotating the connector arm inboard, until the connector is firmly locked in place on the module assembly.
- Grasp the integrated power module with two hands and install the assembly on the battery tray (Scheme 355)
- Install the integrated power module retaining bolt and screw.
- Connect the gray connector on the integrated power module housing.
- Install the B+ terminal cable and nut on the integrated power module B+ terminal. Snap the cover in place.
- Connect the negative and positive battery cables.
The Front Control Module (FCM) is a micro controller based module located in the left front corner of the engine compartment. On this model the integrated power module must be positioned aside in order to access the front control module. The front control module mates to the power distribution center to form the Integrated Power Module (IPM). The integrated power module connects directly to the battery and provides the primary means of circuit protection and power distribution for all vehicle electrical systems. The front control module controls power to some of these vehicle systems electrical and electromechanical loads based on inputs received from hard wired switch inputs and data received on the PCI bus circuit (J1850).
Scheme 355
For information on the Integrated Power Module Refer to POWER DISTRIBUTION .
As messages are sent over the PCI bus circuit, the front control module reads these messages and controls power to some of the vehicles electrical systems by completing the circuit to ground (low side driver) or completing the circuit to 12 volt power (high side driver). The following functions are Controlled by the Front Control Module
- Headlamp Power with Voltage Regulation
- Windshield Wiper "ON/OFF" Relay Actuation
- Windshield Wiper "HI/LO" Relay Actuation
- Windshield Washer Pump Motor
- Fog Lamp Relay Actuation
- Park Lamp Relay Actuation
- Horn Relay Actuation
The following inputs are Received/Monitored by the Front Control Module
- B+ Connection Detection
- Power Ground
- Ambient Temperature Sensing
- Ignition Switch Run
- Washer Fluid Level Switch
- Windshield Wiper Park Switch
- PCI Bus Circuit
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.
Two power outlets are utilized on this model. One in the instrument panel center lower bezel 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.
A relay (Scheme 356) 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.
Scheme 356
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.
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.