Next to a good scan tool, I think having a good scope is vital to diagnosing today’s cars. A scan tool will tell you what the control module is “seeing”, but a scope will tell you if the module is being told the truth by allowing you to see the actual input from the sensors.
The scope you choose should be in line with your needs and your budget. There are a variety to choose from, but they generally fall into 2 categories: handheld, or PC-based.
Let’s take a look at the two.
What Is A Scope?
When measuring voltage, there are three tools that immediately come to mind. The first is the Digital Volt-Ohm Meter, or DVOM. This tool simply measures voltage and displays it on the screen. Most have a variety of features that allow you to record minimum and maximum readings as well, and certainly they have their place in diagnosing electrical problems.
The next tool is a Graphing DVOM. This tool now allows the measurement to be plotted on a graph over time, allowing the user to see the variances in the signal as they occur.
Last is the DSO, or Digital Storage Oscilloscope. The DSO, too, graphs the voltage signal over time. The BIG difference between all three is the rate that each samples and records these signals. Let me back up a bit. Each tool “samples” the signal and then plots the average to the display screen…whether in a numerical value or as a graph. The accuracy of the reading is impacted, therefore, by how many samples per second the tool records and averages. The more samples taken, the more accurate the reading. Of course, there are variances inherent in each tool as well that need be taken into consideration. The typical DVOM may sample at the rate of 200-400 samples per second, as compared to a good DSO with a sample rate of 20 MILLION samples per second.
Now consider the speed at which some input signals occur. As a reference, the typical spark plug takes 1.5 milliseconds to “fire”, and we’ve all seen a spark jump it’s gap. The graphing meter or DVOM just can’t sample fast enough to catch imperfections in signals operating at this kind of speed. And that is just one area where a scope shines!
In addition to measuring voltage, a scope can be used to measure pressure, vacuum, and current with the right accessories. These abilities allow a good scope user to perform engine diagnostics faster and easier. Imagine, for example, testing the mechanical health of a modern transverse V6 in a matter of minutes, rather than hours!
Handheld scopes are more convenient than most PC-based scopes and often more user friendly, with built in databases and testing methods. The Vantage PRO, by Snap-On, is probably the most popular and most capable of the handheld offerings out there. Cost, however, may be a factor for most, with the PRO 2-channel costing more than many PC-based 4-channel units. The key is in how much help you really need…Do you want all the “bells and whistles”?
If cost is the primary factor, then the UEI scope/scan tool may be the choice for you. Having experience with the original UEI ADL7100 scope (I still have it!), I think most beginning scope users will find this scope more than sufficient for most testing needs.
If it’s real diagnostic power you want, though, then PC is the way to go
There are PC and PDA scope options available today, and all offer more power for diagnostics than the conventional handhelds. The ability to utilize higher sample rates, view on a larger screen, and store/record more information allows the user to find those elusive “glitches” that a handheld may miss.
PICO scopes are at the forefront of automotive PC-based scopes, and are competitively priced to handhelds. Unlike the databases in most handhelds, updates for the PICO are free. Because of their early relationship with Tom Roberts, PICO has become the top choice of techs looking for PC scope applications.
There are also other choices in PC scope software/hardware, and I encourage you to do your homework when comparing. Remember, tools are an investment in your productivity and their cost should be compared versus their benefits. Keep in mind, too, that any scope is only as good as the user. Make sure the tool you choose…and the company you choose to purchase it from…will be there to help you learn how to get the most out of your new scope!