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A word about your vehicles electrical system

     Today's vehicles consist of about 6,000 feet or 90 pounds of electrical wire. Earlier vehicles in 1948 had about 150 feet of wiring. In addition to the wiring on today's vehicle there can be up to 90 ECU's (Electronic Control Units) or also known as computers in a modern vehicle. These ECU's receive and transmit electrical signals to a wide array of electronics in our vehicles and sends an output signal to them or receives an input signal from them. These electronics control most of the operation of the vehicle from bumper to bumper. Most of the ECU's are also connected to a Controller Area Network (CAN bus) which is a vehicle bus standard designed to allow the ECU's to communicate with each other in applications without a host computer. These communication signals are in the form of voltages and grounds.

     Electrical signals can be intermittently interrupted or blocked in many ways like water intrusion, heat, vehicle accidents causing wiring or component damage, vibration, Galvanic corrosion, loose connections on connectors or grounds, poor design or just failure due to the age of the component. The signal can be transmitted in a device as simple a $0.50 on/off switch or a $1,000 computer.

     Switches on your vehicle are either what is called a pull-up or pull-down switch. A pull-up switch gets its power straight from the battery and could have fuses and relays feeding it. A pull-down switch gets it power from the computer and is grounded on the output side of the switch when activated. Both of these can be tested thru proper testing techniques by fooling the computer that the switch is activated. Extreme caution should be used in this testing for you could fry a computer driver.

     Relays are a control device. They control high current items like fans, lights, horns, AC compressor, etc. and use a low current coil side to activate the high current switch side. There are several ways to test these but some are better than others. If you think that you can test them by hearing or feeling them click, that is not a good test. If you think you can pull them out and supply power and ground to the coil side and get continuity on the load side, then you again have tested this incorrectly, for the contacts inside the relay could be burnt and causing high resistance. Relays should always be tested under a load.

     Continuity testing could also give you a false result of a what you may think is a good wire. The wire should also be placed under a load when testing. This is due to the resistance in the wire and the possibility of it being shorted, or broken. If your voltage stays the same but the resistance increases, then the current will decrease. If the resistance decreases, then the current will increase and the device will work correctly. Take for instance you kink a water hose (causing high resistance) with a sprinkler attached to the end of it. This will increase resistance at the kink and the sprinkler will not function proper. Voltage drop testing will show this difference in potential.

     When problems arise on our vehicles the ECU's will store a fault code known as a Diagnostic Trouble Code (DTC). This fault DTC can be a hard fault which means the problem is happening now or a fault which has occurred. These codes can be retrieved with an On Board Diagnostic (OBD II) scanning computer thru the Data Link Connector (DLC) which is generally located below the driver's side instrument panel. Sometimes you may not be able to communicate with the vehicles computers due to various problems. An example of this is bad wiring or blown fuses. Another way is if a computer is malfunctioning and not operating correctly and may either not transmit data signals or just totally scrambled the data signal and can cause a total lack of the OBD II scanner to communicate with the Powertrain Control Module (PCM) or other ECU's. For example, suppose you and I were on a three way call with a friend. Now you and I are talking with each other and the third person suddenly starts screaming to the top of their lungs. Now you and I can no longer hear each other. That's what I call a screaming ECU / computer. It would now have to be determined which ECU is malfunctioning. This has happened to me just recently in which one bad ECU caused no communication with the entire vehicle computer system with my scanner. I isolated the bad ECU and system returned to normal with full communication. When ECU's are replaced they may or may not be plug and play units. Most have to be flashed for the vehicle type that it's in. Some ECU's can be repaired without flashing.

     The most important electronic component in a vehicle is the Battery. It must also be the correct size and output CCA for the vehicle as well. The connections must always be tight, clean and free of corrosion. The Alternator / Generator is also a highly important electronic unit. The alternator actually generates an AC voltage like what is used in your home. This AC voltage is converted to DC voltage by the internals of the alternator. There is a maximum amount of AC voltage that is allowed to pass into a vehicles system which is .3 volts or 300 mv's. Too much AC voltage allowed into the system will cause major drivability problems which causes AC ripples into the DC system. If a diode in the alternator becomes faulty, the DC output is also faulty. The amperage output will be regulated by the PCM due to the various systems that may be operating on the vehicle like the head lights, cooling fans, AC, radio, etc. So not only should voltage be checked when checking an alternator, but also the amperage.

Most problems with electronics on a vehicle are ground related. Meaning a faulty or missing ground or a system circuit grounded out. Electrical testing fault issues on a vehicle can be challenging and time consuming. A wiring harness can contain up to 100 or more individual wires. Let along the tight spots that electronics and connectors are placed in. But with more convenience, when there is a problem, there is inconvenience.

     I can't promise that we can find or fix every electrical issue that might come in and most all other mechanics would agree with me. However, I learn from the best, including my Father who is a wiz on electrical. Years ago he was helping me on my Jaguar that had an electrical issue. I stated to him that this design was a piece of CR_P. His reply was "No it's not, it's a well-designed and engineered piece of equipment" and explained why. None of us know everything about every vehicle, even though most electrical test that we do are performed about the same on most all vehicles. Also, vehicle manufactures do not give out all their information on every vehicle and some test equipment can get very expensive. Just remember that an ignored repair of an electrical system problem can lead to additional items failing depending on the system it operates or a total loss of the vehicle. Something I taught a friend of mine after I noticed him taking out the seats in a truck. I ask him if he had checked the battery and fuse first. Well don't go to the electronic component and start you're testing there, as he learned the hard way. It was the fuse and not the component.

     My name is Scott, and my brother Russell can both be reached @ 225-44-FIXED, 225-443-4933, and our business name is "Xtreme Auto Repair". Interest free financing is available for those in need.

     Our business hours are M-F 7:30am-5pm, Saturday 9am-3pm. All calls after hours goes to our voicemail, please leave a message and I will return your call the following business morning. Please check out all of our pictures, videos and reviews listed on GOOGLE. They reflect our work.

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