While replacing a blown head gasket and re-torquing the head bolts, you reach into your tool box and grab your 1/2-inch impact and rattle the bolts down. Just kidding! You would reach for your torque wrench and accurately follow the manufacturer recommendations for torque patterns and values. To guarantee a quality repair, an accurate torque wrench is mandatory – one that has been calibrated.
It is no different when choosing your electronic test equipment. The accuracy of your repair depends on the accuracy of your readings. An accuracy spec with a difference as low as 0.1% can throw off your results in sensitive circuits, causing you to incorrectly assume a component is defective. Buy the best you can afford, and make sure that you also check the small print, i.e., the specifications. The tighter the specs, the more accurate your results.
So why use an oscilloscope when other equipment can fix most problems? The answer is speed. And not necessarily the speed of diagnosis, but rather the speed of the signals you’re looking at.
Many things affect the readings taken from a piece of test equipment. Bandwidth (the maximum frequency a scope can display), the number of samples taken per second (the more the better) and the glitch capture capabilities (the lower the better) make up a quality scope. The better the specifications, the better the results, and the more likely you are to find the problems you are looking for.
You don’t want to make this expensive purchase again, so buy a quality product that will grow with you as your abilities improve.
Baselining a Vehicle
Body temperature, blood pressure and a thorough debrief are required prior to obtaining care from a physician. Why should service on a vehicle be any different? Over time, connections can loosen from vibration, oil and water leaks, causing deterioration of wire insulation, and previous repairs improperly conducted may create poor grounds and incorrect voltage values for the vehicle’s processor.
Most scopes provide a means to record sensor and actuator values in memory. These “baseline” signals can be stored in a computer for easy comparison if the need arises. What better reference than known good waveforms stored from the precise vehicle exhibiting a problem. Sensors, actuators, connections and components will degrade over time. Their values may fall to limits set by the manufacturer to illuminate a MIL (Malfunction Indicator Lamp), or they may not. Perhaps their operation has degraded to the point of a driveability problem that will not store a code.
Preventive Maintenance For Customers
Look for additional capabilities as well. It is much easier to sell your customer on a costly repair after presenting them with before and after pictures. A scope with printing capabilities is important, as well as is the ability to communicate with a computer.
The second-most costly investment for most of us is our transportation. With the costs of new vehicles on the rise, more people are maintaining their “old paint.” As each of us get older, it becomes more and more important to get yearly checkups. This provides us with timely information imperative to maintaining our health. Vehicles are no different. Preventive maintenance provides a clear identifier for pending failures.
Preventive maintenance is also a necessary part of customer care. Offer a portfolio containing this information to your customers. They will find it useful when trading-up to a new vehicle and can provide a professional package to the new owner.
Cause and Effect Clearly Displayed
The underlying quality ingrained in all of us is curiosity. Curiosity drives our abilities to new peaks and the level of our work to perfection. Spending too much unnecessary time diagnosing a problem, replacing unwarranted components and confusion over system operation have plagued all of us from time to time.
With your eyes closed, envision the operation and illustrated parts breakdown of a carburetor. How do the parts interact and combine to make the whole? Now envision a simple circuit and follow the electrons through the wires as they make their way from the battery through the switch, past the light filament to the ground and back to the battery. We can only imagine what this sensation is like.
A lab scope offers a window into the world of electronics. View the patterns that make up this magical world and act on fact, not on guesswork. Read the patterns as you would a story. Start on the far left and imagine what happens as the voltage increases and decreases over a small slice of time. Watch as the driver transistor, an electronic switch, pulls the signal to ground allowing current to flow through the injector coil. Measure the height of the inductive kick from the coil and watch as the open circuit voltage again returns to battery voltage awaiting the next actuation.
The lab scope has become the tool for the 21st century diagnostician. Faults hidden deep within wiring connecting sensors and actuators to their controllers can be located with pinpoint accuracy. As the use of electronics becomes more invasive in the automobile, tools and techniques used by engineers for decades must be accessed. The true cause can be found without costly trial and error mistakes.
It’s important to watch the flow of the waveform, and in time, you will develop a feel for what’s right or wrong after working with the scope. That’s why it’s important to practice with your scope; get to know what certain patterns look like. Compare the results from one vehicle to another. And, when times are slow, rather than cleaning the tools in the toolbox, get out the scope and take some measurements. Then store your results on a laptop computer and develop a database. Similar to taking notes in school, building your own database of known good and bad signals is a must. There are a number of similarities between signals taken from sensors and actuators on different vehicles. These patterns can easily be recalled and examined, and in some cases, used by the equipment making the test.
Armed with this information, a detailed analysis can be made of a circuit’s operation and a determination can be made on where to focus your time. There are several software database programs available that act as “electronic file cabinets” designed to increase your comprehension and provide a means to store related patterns.
Some scopes already contain an electronic file cabinet for storage and retrieval of your waveforms. These programs can come with more than 200 known good and bad waveforms sorted by vehicle, engine and signal type and allow bi-directional communication between your computer and the scope.
When time permits and the work slows around the shop, bring in a vehicle and baseline it. Store a number of common signals into your database. Oxygen (O2) sensor, manifold absolute pressure (MAP) sensor, engine coolant temperature (ECT) sensors, throttle position (TP) sensors, fuel injector (FI), mass air flow (MAF), are all good candidates, as well as ignition, charging system and voltage drops – just to mention a few.
Any tool is a great tool, as long as you understand its limitations and find a good use for it. Don’t let a tool, such as a scope, sit in your tool box and gather dust. Take the time to learn how to use it.
When selecting a lab scope, look for one that is easy to use. Look for features and functions that make your diagnosis easier and more accurate. Be aware that electrical noise can alter your results, so look for either shielded cables or use a “twisted pair.” A twisted pair simply means that you should braid your test leads so that noise is canceled out.
Now that you have some tips on how to use the scope more effectively, get out there and sell the scope work to your customers and let it pay for itself in no time.