IF YOU CAN DRIVE IT, WE CAN FIX IT  !​ Affordable Car Repair Knoxville, TN.

Excerpt From :

AAA Guide To Auto Repair PDF

"TODAY’S CAR
A MOBILE COMPUTER NETWORK
In the 1980s, automakers began using
computers to help control engine exhaust
emissions. Since then, computers have
become smaller and more powerful, and
their automotive uses have grown far beyond
engine control. Cars today can contain
dozens of microprocessors that constantly “talk” to one another over a local area
network. These processors control not just
the engine, but most everything else as
well – from interior lighting to GPS satellite
navigation.
The good news when it comes to understanding computer-controlled systems is that they all work in basically the same way. Here’s a
INTRODUCTION
Few of us enjoy taking our car into the shop. It’s
inconvenient and costs money we would rather spend on something else. Media reports of repair industry dishonesty don’t help. They make even the savviest among us feel a twinge of paranoia when we enter a garage. Then, when it’s time to pay, we often pull out our checkbook or credit card with a nagging fear that we are being overcharged.
Although our concerns about auto repair may be
partially justified, they are often aggravated by one
or more of the following factors:
• We don’t understand how modern automobiles
work. This was true back when cars were completely mechanical devices, and it’s even more true today when computers and technology impact nearly
every part of the vehicle.
• We lack confidence in our ability to recognize
and explain our automotive service needs. The
maintenance and repair of modern cars differs
from that of older vehicles, and a lack of clear
communication is the single biggest cause of auto repair dissatisfaction.
• We don’t always grasp the estimating process, or what it means when we are quoted a price to
diagnose or repair a problem. Ironically, a good
estimate is a powerful tool for reducing repair-
related stress.
• We are concerned that the person working on our car may not be able to fix it right the first time, or may cause additional problems.
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simplified explanation of how a modern
automotive engine control system operates:
• Sensors on the engine and throughout
the car gather information on the current
operating conditions. Common sensors monitor throttle position, coolant temperature, intake
manifold pressure, crankshaft position,
engine rpm and vehicle speed.
• The sensor signals go to a computer called the
Powertrain Control Module (PCM) that evaluates
the inputs and generates various outputs to
optimize engine performance, exhaust emissions and fuel economy.
• The PCM output signals control actuators that
regulate engine rpm, fuel delivery, spark timing
and other powertrain components and systems.
Actuators come in many forms, but the most
common are electric relays, motors and solenoids.
Modern electronics have helped make cars more
reliable. The vehicles of today require far less
maintenance than older cars, and many routine
services such as the “tune up” are required less often
or have been eliminated altogether.
However, electronics have also made cars more complex. This can make identifying the source of a problem more challenging. Even though today’s technicians and tools are better than ever, diagnosing problems on modern automobiles is generally more time consuming – and therefore more expensive – than in the past.
Tracking Down A Problem
To help understand how a “simple” repair may take a while to diagnose, let’s consider a common problem and its possible causes. Imagine your car has begun to hesitate when you press down on the accelerator. In a 1970s vehicle without computer controls there were around half a dozen common causes for such a problem. But, on a modern car here are just some of the possibilities a technician may need to check:
• Low fuel pressure – faulty fuel pump
• Low fuel pressure – clogged fuel filter
• Low fuel pressure – faulty fuel pressure regulator
• Dirty injectors that deliver too much or too little fuel
• Faulty spark plugs or spark plug wires
• Faulty ignition module or coil pack
• Defective mass airflow sensor
• Defective air charge temperature sensor
• Defective coolant temperature sensor
• Defective throttle position sensor
• Defective manifold absolute pressure sensor
• Defective camshaft position sensor
• Defective crankshaft position sensor • Defective exhaust gas recirculation (EGR) valve or its position sensor
• Faulty power or ground connections in the
engine control system
• Defective PCM, or one that needs to be
reprogrammed
• Excessive exhaust back pressure
• Excessive carbon build-up in the engine causing
a knock and retarded ignition timing
• Incorrect fuel use (octane too low) causing
a knock and retarded ignition timing
• Improper torque converter clutch engagement
Because the number of potential problem sources has grown, automotive diagnosis today requires well-trained and properly-equipped technicians who employ systematic diagnostic processes based on both formal training and real-world experience. We’ll have more to say about technicians later, but right now let’s consider a common diagnostic procedure that is often misunderstood by repair customers.
Computer Diagnosis
What Does it Mean?
What comes to mind when you hear the words, “your vehicle needs a computer diagnosis to find the problem?” Do you envision a technician
connecting the car to a big machine with
flashing lights that “beeps” a few times then prints out a description of the problem and its solution? Unfortunately, it’s not that simple.
Modern electronic engine control systems “know” and monitor the operating parameters of every
component. When the
input from a sensor falls outside normal limits for
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too long, or the output signal to an actuator
repeatedly fails to generate the expected result,
the PCM stores a Diagnostic Trouble Code (DTC).
If a stored code indicates a problem that may
increase exhaust emissions, the PCM also illuminates the “Check Engine” light on the dash. However,
many types of codes can be set with no indication
to the driver.
To access DTCs, technicians connect a “scan” tool
to a Diagnostic Link Connector that is commonly
located under the driver’s side of the instrument panel. The scan tool displays any stored codes, and many motorists think that’s where diagnosis ends. They question why they should have to pay,
sometimes dearly, for such a simple procedure.
In reality, pulling trouble codes is just the first step in a computer diagnostic procedure. DTCs don’t tell you if a part is bad, they only indicate that the computer has seen something it didn’t expect in a particular
circuit. The problem may be the part associated with the trouble code, but it could just as easily be a shorted or open circuit in the part’s electrical wiring.
Sometimes, trouble codes are set when there is nothing wrong with the engine control system. This happens when a mechanical problem, like a vacuum leak, creates engine operating conditions that cause a sensor to generate an out-of-spec signal. The PCM will then attempt to compensate, which may cause an actuator to operate outside its normal range, setting yet another trouble code!
To help pinpoint the problem, a technician must
perform additional tests. These can range from
mechanical checks, like engine compression, to more in-depth electronic diagnosis. One common operation involves using test equipment to access the engine control system network data stream. This allows
the technician to view real-time sensor data and manually operate the system actuators.
The ability to determine which additional
tests are needed, and to accurately interpret both test results and computer network data,
comes from training and experience. Today’s technicians use vehicle computer diagnosis in much the same way surgeons employ medical testing. In both cases, combining test results with expert knowledge and skilled hands can lead to a diagnosis and a cure.
BETTER COMMUNICATION
=BETTER SERVICE
Not every automotive problem requires
computer diagnosis. In many cases you may
hold the key to unlocking your vehicle’s
problem. After all, you know your car better than anyone else, and will be first to notice when its performance changes. The more
information you can share with the technician about what you are experiencing, the better prepared he/she will be to identify the problem in a timely and cost effective manner.
When discussing car trouble with a shop, some drivers will offer a diagnosis or request a specific service operation. They think this makes them appear knowledgeable, or hope that by asking for “just a tune-up” they can limit the repair costs. Unfortunately, this approach often results in spending money on work that has no effect on the problem. A much better approach is to simply describe the symptoms your car exhibits.
Putting your observations down in writing
before you head to the shop can help prevent you from forgetting anything. Also, be honest and practice full disclosure. If your vehicle was...." 
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