Unraveling Electrical Problems with Multimeters and Lab Scopes

Unraveling Electrical Problems with Multimeters and Lab Scopes

Today, lab scopes and multimeters are standard equipment in most automotive repair shops. If you’re looking for a new tool or to upgrade yours, here’s a look into their many features and benefits.

Vehicle owners have it easy … well, in a manner of speaking. When their vehicle has a problem, they simply turn it over to their repair shop and let the service technician find the source of the problem and fix it. At that point it’s up to the technician to dig into his toolbox, find the right tool to diagnose the problem first and then solve it.

scopes-electricalWith systems on cars becoming more complex and computerized, it is highly likely that the problem is electrical. When an electrical problem is simple enough, a regular multimeter is sufficient for the job, but when it is an intermittent electrical failure – the kind that most technicians know is extremely tough to diagnose – the sophisticated capabilities of a digital storage oscilloscope, or a “lab scope,” are required.

A lab scope is essentially a voltmeter that displays voltage signals along a timeline. Lab scopes became popular in the mid-1990s when on-board diagnostics appeared on the scene. Today, lab scopes are standard equipment in most automotive repair shops. In fact, they are indispensable for professional technicians working on advanced diagnostic problems.

At Paoli Auto Repair, Dominic Minuni, ASE Master Tech and Ford Master Tech, said that while he may use his multimeter practically every day, he is likely to use the lab scope only once a week. According to Minuni, the multimeter displays the existence of the signal, but the lab scope not only displays the signal, but also shows if there is any breakdown or glitch in the signal, proving that the particular part being tested has a problem and might need to be replaced.

Lab scopes are available in both analog and digital versions. They range from basic hand-held versions to advanced, digital PC-based, multi-channel ones. However, a digital lab scope is a better choice for shops that work on a variety of late-model vehicles with many high-end cars and SUVs that have very complex engine management systems.

The price of a 4-channel, PC-based lab scope usually runs pretty high – into thousands of dollars – but its usefulness in performing diagnostic work, especially with faulty injectors and sensors, wiring and connectors, cannot be underestimated. Some of them do not require their own separate power source and can run off a laptop or come as a stand-alone unit. There are lab scopes that are tied into diagnostic databases with good refresh rates. This is a feature that can save a technician many hours of diagnostic labor time.

According to shop owner Chuck Wichrowski of Baum Boulevard Automotive in Pittsburgh, PA, “At our shop we service all types of cars and therefore, want a unit that provides the most coverage – European, domestic and Asian. We would want a unit that connects directly with databases for repairs, has sample graphs that show what is normal for that car, and can help in reprogramming the modules and the ECM.”

All scopes operate pretty much in a similar fashion. The only difference is in how you get to the menu selections on a particular scope. The key to using a lab scope is to know how to set it up properly in order to view the signals correctly. Since the laws of electricity never change, the waveform on the screen cannot change either – ever. They will always be displayed as voltage over time. It is always a better idea to view a “good” waveform and compare it to what you see on the screen rather than look at a “bad” one. Some manufacturers have a menu of patterns built in. Finding a good wave pattern to compare with is essential to diagnosing and solving intermittent electrical problems.

Along with your lab scope you will need accessories such as adapters, current probes, back probes and piercing probes, gators, pressure transducers, test leads, test clips, and software and cables – all depending on the instrument that you buy and the nature of the work you perform.

A multimeter, on the other hand, is an electronic measurement tool that combines several measurement functions in one unit. It is designed to safely and accurately measure electric current, voltage and resistance. It is available in analog or digital versions with a variety of features and at various price points. The analog version has a moving pointer to display readings, while the digital version offers a numeric display and may show a graphical bar representing the measured value. The digital multimeter is not too expensive, is more common and very useful.

John Ranney, owner, European Auto Tech in Tucson, AZ, frequently uses a multimeter. According to Ranney, “There are a lot of fancy rigs out there, for sure. But I need something that is easy to hook up and drive with. I like using a small toolbox to quickly sort out a problem. I don’t need to bring the shop with me. Keep it simple.”

However, when traditional methods of diagnosing a problem do not work using a multimeter, a lab scope can be very helpful. Whichever lab scope you ultimately decide to purchase, learning when to use it and how to utilize its various features and capabilities is critical to performing a successful diagnostic job.

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