Every three years, or so it seems, I go through a major updating of my diagnostic equipment because that's how fast automotive technology is changing. Looking back to 1981, when on-board diagnostics were introduced, I bought my first scan tool. By the late 1980s, I discovered the on-board diagnostic systems were simply too crude to give me all the diagnostic information I needed. So, I bought my first digital storage oscilloscope (lab scope) to display voltage and time base signals from sensors and actuators in the engine management system. At the time, lab scopes were a huge leap forward in diagnostic technology.
By 1996, I began buying On Board Diagnostic (OBD) II equipment designed to record a complex array of diagnostic monitors, freeze frame data streams, and literally thousands of diagnostic trouble codes (DTCs). As the decade of the 1990s closed, auto manufacturers began networking engine management, automatic transmission, anti-lock braking (ABS) and body-control computers via multiplexed wiring systems. Since multiplexed systems are difficult to diagnose with voltmeters and lab scopes, I began buying scan tools that would display power train, ABS and body control data, as well as perform the necessary technician-initiated or bi-directional control functions needed to diagnose these systems.
In 2004, the Controller Area Network (CAN) systems were introduced, which allowed networked, multiple on-board computer systems to communicate with each other in a faster, much more efficient manner. In response, most scan tool manufacturers added CAN adaptors to existing scan tools or began designing new scan tools from scratch.
In addition, since many OBD II systems are now at least eight years old and starting to need advanced diagnostics and maintenance, many shops are now investing in scan tools that use bidirectional controls that help locate very small pinhole leaks in the fuel tank and evaporative containment systems. Furthermore, aftermarket equipment manufacturers are also designing equipment that will allow independent shops to 're-flash' or reprogram replacement engine management computers and body control modules.
Editor's Note; For more information on "Flash Programming," see the July issue.
IT'S NOT SO COMPLICATED
Does this technological jargon sound too complicated for the average jobber? At first glance, it does. Nevertheless, let me return to my original point. During the past two years, I've spent at least $10,000 at my local jobber's business on new diagnostic test equipment, with a large portion of that amount bought from my jobber's ignition equipment supplier.
Why should this buying pattern sound so surprising? First, I buy from three sources: our local tool truck supplier, a West-coast electronics test equipment vendor and, of course, my local jobber. In any case, my jobber is as competitive on price and service as the other two suppliers. Second, my jobber is equally competitive on lease-purchasing programs and other types of purchasing options. With that said, let's look at the various selling points of three basic types of diagnostic equipment: volt-ohm meters, lab scopes and scan tools.
DIGITAL VOLT-OHM METERS
The digital volt-ohm meter (DVOM) is the most useful tool for diagnosing electrical and electronic problems. Since most professional meters usually sell in the $300-400 price range, the price might sound very expensive when compared to the $9.95 voltmeter lying in the discount tool tray at the end of your parts counter. Although both measure volts and amps, there are profound differences between voltmeters.
More to the point, professional DVOMs are manufactured with ten-megohms of impedance, which means the voltmeter itself isn't draining current from the electrical circuit being tested. To illustrate, many airflow sensors are designed to produce 0.7 volts at idle. Instead of correctly indicating 0.7 volts, a cheap voltmeter might indicate 0.5 volts at idle, which would lead a technician to mistakenly install a new airflow sensor in an attempt to cure a fuel delivery problem.
As for features, a good professional meter should have a minimum and maximum or min/max recording feature, which records the lowest and highest readings in a circuit. The best meters have a "fast" min/max feature that records voltage fluctuations down to 250 millionths of a second, which is handy for diagnosing loose electrical connectors and other glitches in electrical systems. In addition, a professional DVOM should measure on/off duty cycle relationships, electrical frequencies, millivolts and milliamps, alternating voltage and current, electrical pulse widths in milliseconds and have a lighted screen for use under the dashboard.
The utility of a DVOM can be greatly enhanced with the addition of a pressure/vacuum transducer, a low-current amp probe, a high current amp probe, and perhaps a temperature transducer. The low-current amp probe with a range from about ten milliamps to 60 amps is the most useful in electronics diagnostics, since it can be used to measure very low current flows in fuel injector, primary ignition, and other electronic circuits.
The technical term for lab scope is "digital storage oscilloscope or DSO." Unlike a "real-time" or "live" lab scope, the DSO stores and processes an electronic signal for a short time before it is displayed on its screen. Although many advanced auto technicians do indeed use real-time lab scopes, most use a downsized, digitalized variation called a DSO designed specifically for automotive use.
Unlike a DVOM, the lab scope displays a voltage signal as it is related to a time base. A crankshaft sensor voltage signal, for example, might vary from zero to plus or minus 2.5 volts. The DSO displays the crankshaft sensor signal on as a waveform crossing a lighted screen. In addition, the DSO might indicate that the signal is occurring at an interval of 250 thousandths of a second and rises or falls at a specific rate.
DSOs range in price from less than $1,000 to over $6,000. Quite obviously, the price has much to do with a DSO's overall capabilities, which are too numerous to describe in this space. Overall, an entry-level DSO will do at least 90 percent of all the electronics testing required in an average repair shop. The more expensive DSOs have extensive high-voltage, secondary ignition display and storage capabilities that may not be required by the average technician. In any case, a DSO can effectively utilize the same transducers and amp probes used on the DVOM to display pressure, temperature and amperage as a waveform value.
Scan tools range from simple trouble code readers priced at slightly over $100 to OE-supplied units selling for as much as $6,000, with the average being slightly under $3,000. As for overall capabilities, only an OE-supplied scan tool offers a complete array of diagnostic capabilities. The downside, however, is the tool is manufacturer-specific. Aftermarket tools, on the other hand, sacrifice many less essential diagnostic capabilities in order to cover many different vehicle lines. In the most common diagnostic scenarios, an aftermarket tool will have at least 95 percent of the capabilities needed to diagnose and repair the vehicle.
Most professional aftermarket tools will display generic or federally mandated diagnostic data along with enhanced OE-based diagnostic data. Professional tools also graph most diagnostic data and should be able to record, store "movies" of vehicle malfunctions, and download them to a laptop or desktop computer. Most important, a professional scan tool should have the necessary bi-directional control capabilities needed to command various engine, power train and body control to operate in accordance with the technician's commands.
Last, the most recent generation of scan tools are incorporating flashing capabilities needed to reprogram the various computers and modules found throughout the modern vehicle. A PCM, for example, must often be reprogrammed to cure various performance maladies. Various replacement chassis modules must be flashed to make the module compatible with the vehicle's on-board electronics system.
Although flash technology is in its infancy and not currently cost-effective for most independent shops, it will become a future requirement to repair module-operated power windows, door locks and windshield wiper motors. In response to this demand, aftermarket tool manufacturers are currently manufacturing nameplate-specific reprogramming kits for current scan tools or are manufacturing stand-alone tools designed for reprogramming a wide variety nameplates and modules.