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Body Electrical: Wiring and Power Distribution
Written by PFM Staff
Ed Note: Charger Technician Training, in a wide variety of 2-day training blocks, is available at dozens of Chrysler training locations across the United States. There is no prerequisite for the training, and it is open to all fleet personnel, from the fleet manager to the maintenance and repair technician. This is the same factory training given to dealership technicians. This same police-specific training will also be available in-house at the police and sheriffs departments running larger fleets of Chargers.
For more information on Charger Technician Training, contact George Bomanski, Fleet Service Manager, Chrysler Group, at 407-257-1532 or via e-mail at firstname.lastname@example.org. This training is scheduled about six months in advance. Because the training is definitely hands on, the class size is limited to 12 techs.
The main purpose of the Charger Body Electrical tech training is to understand the basic electrical architecture in the police Charger, and to understand the many differences between the 2006-2007 models and the 2008-2010 models for diagnostics.
Less than 10% of the DTC fault codes are properly diagnosed, so the Body Electrical course focuses on understanding how the systems work. This includes finding the wiring schematics on the Internet and finding the modules on the car. Half the problem solving is finding the right module and knowing what info that module has.
The Body Electrical course begins with a flashback to trade school: a review of Ohm’s Law. This law of electrical circuits says that the current (in amps) between two points is directly proportional to the voltage drop (the push from positive to negative) and inversely proportional to the resistance between them.
Ohm’s Law is a reminder to use the proper wire size for upfitting, or to select the proper device for the wire size if the wire cannot be changed. It is also a reminder that the amp load on 3 feet of 18 gauge wire is very different from the amp load on 20 feet of 18 gauge wire.
Ohm’s Law also states that resistance may increase at the location where wires are spliced together, or where corrosion has essentially reduced the effective gauge of the wire.
Both the tech for the police Charger and the upfitter for the police Charger must really understand the relationship between volts, amps, resistance and watts. If not, instead of smoke coming from the tires, smoke will come out of the trunk, hood or center console.
Even the slightest increase in resistance at a spliced connection affects the extremely low voltage components. That is why straight solder connections are no longer recommended, due specifically to the reality of poor solder jobs. Instead, crimp and solder, and then protect this connection with marine-grade heat shrink.
CAN Electrical Architecture
The police Charger has three critical and very different Controller Area Network (CAN) data bus systems and a Local Interface Network (LIN) bus system. CAN C is the ultra-fast bus, communicating at 500KB per second. As a “Very High Speed” bus, CAN C is not fault tolerant. It handles the most critical, real-time sensitive devices and systems like the Next Generation Controller (powertrain control module), ABS and the Electronic Stability Program (stability control). That means the slightest problem, like corrosion or broken strands, in the wires into or out of these devices will interrupt their function.
Interior “High Speed” CAN B communicates at 125KB per second. This is still a high speed bus and not very tolerant of faults. Features inside the car like interior and exterior lighting, the audio system amplifier, door locks and gauges are on the CAN B bus.
Finally, Interior “Low Speed” CAN B works at 83 KB per second and as such is more fault tolerant. The automatic HVAC controls, like the hands-free mic in the rearview mirror, are on CAN B. In comparison, the Local Interface Network (LIN) is a very slow bus. The manual HVAC controls like the steering wheel remote radio switches and the tire pressure monitoring system use a LIN bus.
The ignition switch operates on the CAN B bus. In the RUN and START positions, the switch provides wake up sense to a dozen different modules and switches. The ignition inputs to the CCN are switch sense in one of five different voltages with a 5.0-volt reference. For example, KEY IN is 4.04 volts, ACCESSORY is 2.18 volts, RUN is 1.12 volts and START is 0.41 volts.
CAN C, high speed interior CAN B and CAN B are all very different in terms of data rates and fault tolerance. The data rate is how close to real-time the CAN is. CAN C operates with 1.5 to 3.5 volts, while CAN B operates with 0.2 to 5.0 volts. CAN C is not fault tolerant. If connectors are faulted to ground or to voltage, communication is not possible.
CAN B is somewhat fault tolerant. CAN B modules are able to maintain communication with a 3-volt ground offset between modules, or if operating in single wire mode, the tolerance is 1.2 volts. The optimum CAN C termination resistance is 60 ohm maximum, while the termination resistance of a CAN B bus may be 100 ohm.
Pop quiz: What one system on the police Charger communicates over both CAN C and High Speed CAN B? The steering column module. Most of the switches and remote controls operate on CAN B. Since it is a part of the Electronic Stability Program, the steering angle position sensor communicates on CAN C.
The police Charger tech training puts an emphasis on how to use wiring diagrams. All wiring diagrams are shown with the car door closed, the key removed and all circuits timed out. The tech can zoom in/out on all wiring diagrams and scroll left/right and up/down. The electrical architecture for the 2006-2007 Chargers and the 2008-2010 Chargers are very different.
All circuits in the diagram use an alpha-numeric code to identify both the wire and its function. For example, A circuits are battery (B+) feed, F circuits are fused, K circuits are powertrain, T circuits are transmission and Z circuits are grounds. In-line connectors are designated with a C, and then a number that identifies the location. For example, a C100-series connector is in the engine compartment, a C200 means instrument panel, C300 is for the body and C400 is a jumper harness connector. Splices use the same number code, preceded by an S. Grounds are identified with a G and use the same number series.
A connector that plugs into a component (component connector versus in-line connector) is identified by the name of that component W instead of a number. The jumper harness is significant on the police Charger. This 400-series includes accessories, many of which involve the police package.
Power Distribution and IOD
The police Charger has two Power Distribution Centers (PDC). Both receive direct battery power (B+). The front PDC controls most of the power distribution using high side (solid state), push/pull and relay drivers. Two 40 amp fuses in the rear PDC provide power to the front PDC. In the Body Electrical class, every cavity, every driver, every switched and sensed input, every battery feed and every ground in both the front and the rear PDC is reviewed.
In the rear PDC, the Ignition Off Draw (IOD) push/pull fuse is in position 1. IOD is current that flows out of the battery when the ignition is off. This current is necessary for electrical devices like the electronic modules and nodes. These components can be in active, stand-by or periodically-monitoring modes.
After ignition shut off, the admin functions of the NGC (powertrain control module) pull about 300 milliamps for up to 22 minutes. After that the Automatic Temperature Control takes about 90 minutes to settle down. About two hours after ignition off, the Charger with no upfit gear whatsoever is still pulling about 35 milliamps and will continue to do so.
A 35 milliamp draw will run the battery dead in about 21 days. A Charger left unused for any period should have the captive IOD fuse pulled. This prevents the battery from discharging. Pulling this fuse removes power from non-essential, low-current memory functions that are normally on. A detent on the IOD fuse holder allows the pulled fuse to be stored in its cavity but not in contact with the circuit. This is a simple push/pull fuse.
A battery slowly going dead has a very different effect on electronic modules and nodes than a battery that is disconnected. Some modules may throw a DTC when energized after slowly being starved of power.
Pop quiz: How many grounds are on the police Charger? The answer is 18. One of the most important is the engine/trans ground on the right shock tower. That is where the negative jumper cable goes! Of course, not all grounds are equal. The chassis grounds are “dirty” grounds, i.e., they backfeed electrical noise, they carry electrical spikes and they are subject to corrosion. If you need a “clean” ground, connect to the LX body proprietary grounds.
Published in Police Fleet Manager, Nov/Dec 2009
Rating : 10.0
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