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Electronic Workbench - Part I

Introduction

It is the '90's, and no one can deny that we now live in a computer-enriched environment. Automobile transmissions are among the many areas "touched" by electronics. I do believe "computer-enriched" is a good phrase to describe the situation, contrary to what many people think, simply because it is impossible to get the kind of control, over a component, that is possible with "computer-enhancing". For example, automatic transmissions, traditionally, have many hydraulic valves to help shift a transmission, and take into account, certain "inputs" like throttle setting, and vehicle speed, in an attempt at controlling upshifting, downshifting, and shift feel. Now, with newer electronically controlled transmissions, we can, not only monitor speed, and throttle setting, but, now we can monitor barametric pressure (to compensate for differences in engine horsepower output that varies directly with altitude and other barametric pressure variables), outside temperature, transmission temperature, True engine load (rather than merely throttle setting), Airconditioning status, 4wd status, transmission condition (comparing the amount of time it takes for a transmission to complete a particular shift, the computer can compensate for a worn out transmission, by boosting control pressure, or shift apply volume), as well as many other things, to make an engine/transmission combination perform more efficiently. I believe that there are some definate improvements with this electronically controlled environment, but, as with anything else, as you complicate things, there is a potential for problems, and, of course, solutions to those problems.

To solve these problems successfully, we must first identify the cause of the problem, and then, come up with the correction to the problem. Many of the troubleshooting problems I have seen through my e-mail questions tend to be caused by general lack of understanding of how the problem circuit actually operates. Without knowing how a particular component operates, it can only be "by accident" that the cause of the problem is found. This concept extends way beyond electronic problems; You MUST understand exactly how something is supposed to work before you can accurately find the cause, and the solution, to a particular problem. One of the largest problems, I have encountered while answering e-mail, happens to be assuming certain "basic" concepts, that I take for granted, and assume that "everyone" knows already; This is my fault, and it happens to be one thing that annoys me about learning how to computer program; programming books are written by programmers that tend to forget that a beginner is reading the book, and tend to assume too many things that they, themselves, take for granted, and have always assumed were "common knowledge". I am guilty of the very same thing. So, with this in mind, we are going to "crawl before we walk, and, eventually, run", and learn some basics on electricity, before we learn how pulse width modulation works in a 4L80E transmission, or how various sensors are used as inputs in a complete "drive train module" in a vehicle.

Electricity: The Basics

In order to troubleshoot an electrical circuit, you must first understand some basics regarding electricity. There are several terms that are important, but, often misunderstood; among them, are: Conductor, Insulator, Voltage, Amperage, Resistance, Battery, and Complete Circuit. It may help to use an plumbing analogy, because fluid routed through pipes, may be easier to visualize for most people.

Conductor: A conductor is anything that will allow voltage to pass through it. Wires are examples of electrical conductors, as well as pieces of metal, such as engine blocks, transmission cases, automobile frames, etc. It is the number of "free electrons" that defines whether a substance is a conductor, or an insulator. A "conductor", in our plumbing analogy might be the inner volume of a pipe where fluid flows, for example, while an insulator might be the walls of the pipe, that do not allow fluid to leak to the outside of the pipe, just as an insulated wire might use Copper strands as the conductor, providing a path for electricity flow, and a plastic coating as an insulator, around the outside to contain the electricity.
Insulator: An insulator is anything that will not allow voltage to freely pass through it. Wire insulation, plastic, and other similar substances are examples of insulators. Again, the walls of a pipe, would serve as an insulator in our plumbing analogy.
Voltage: Voltage, is the "pressure" in the circuit. Similar to water pressure in a water pipe, Voltage makes the electricity "flow" through a conductor, just like water "flows" through a water pipe, as a result of pressure being higher on one end, than the other. Without a difference in pressure, fluid does not flow through the hose, and, without a difference in voltage potential, from one end of the wire, to the other, electricity does not flow.
Amperage: Amperage is the "flow" of electricity through a circuit. The amount of water passing through a pipe, could be referred to as the "flow" or volume of water, and, so amperage is the "flow" or volume of electricity passing through a circuit. One interesting thing to note: As you increase the pressure differential in a hose carrying fluid, fluid volume increases; similarly, amperage increases as the voltage potential rises, within a circuit.
Resistance: Resistance refers to the ability of the circuit, or portion of a circuit, to attempt to stop the flow of electricity. Pinching a water hose could cause a resistance to the flow of water through the hose, just as adding resistance to an electrical circuit will cause the flow of electricity, or amperage, to slow down. So, all else being equal, if you reduce the amount of resistance in a circuit, the flow will increase. Resistance, in our plumbing analogy, can be defined by the overall size of the hose, or the length, or the size of any restrictions, so doubling the length of a given hose, while keeping the pressure the same, will slow the flow of fluid in hose, and reducing the diameter of the hose, will slow the fluid flow, as well.
Battery: A Battery is simply a storage device for electricity. By storage, I mean that a battery does not necessarily create electricity (It does chemically, but, for the purposes of discussion, I would prefer that you assume that it does not Create electricity), but only stores electricity. What I mean then, is that just because a battery is "dead" does not necessarily mean that it is the battery's fault, any more than an empty bank account (like my bank account...) is the bank account's fault. If you do not put electricity in, you do not get electricity out. The "battery" in a water system could be a storage tank; if you continue to use water from the storage tank, without ever filling the storage tank, the tank will eventually be empty.
Complete Circuit: A Complete Circuit simply refers to the "path" that the electricity takes through the circuit. Electricity must flow in a complete circle, from the battery, through the circuit, and back to the battery. If the flow is interupted, anywhere within the circuit so that the electricity cannot make it back to the battery, electricity stops flowing completely and would be similar to shutting off the water faucet. There are two different theories concerning the direction of flow, through this circuit. One says negative to positive, and the other says positive to negative, but, no matter which one you accept, it is sufficient (for our purposes in electrical diagnostics) to know, only, that it does flow, within a complete circuit.

Concepts based on the previous definitions

Increased Voltage causes increased Amperage, as stated above.: All else being equal, increasing Voltage within a circuit increases Amperage within that circuit, just like increasing water pressure would increase water flow through your water hose.
Increasing Resistance decreases Amperage.: If you increase Resistance, you decrease Amperage, just as you increase resistance in a water hose (by pinching it), which causes a decrease in "flow" of the water through the hose.
Resistance causes reduced voltage "downstream" in the circuit.: Here is where it gets a little tricky for some people to visualize. If you cause a resistance in a circuit, the voltage on the other side of the resistance is lower than the first side, just as pinching the hose, causes high pressure on the faucet side of the hose, and lower pressure on the pinched side of the hose. The "tricky part" is understanding that there is pressure at the faucet, lower pressure just beyond the pinch in the hose, and still lower pressure at the end of the hose, far beyond the pinched part. So, for example, there may be 20 pounds, per square inch, at the faucet, 11 pounds, per square inch, at the other side of the "pinch" and only 5 pounds, per square inch, at the end of the hose. In this example, if you checked the pressure difference at both sides of the "pinch" you would read 9 pounds, per square inch (20 minus 11). Similarly, if you have a 12volt source, at the battery, and, within a circuit, you have a resistance, causing the 12volts to drop to 10 volts, on the "other side of the resistance", you can hook up a voltmeter (a tool to measure voltage), to both sides of the resistance, and you will read 2volts (the difference between the 12volt source, and the 10volt result).