Lab Scope Diagnostics Training Tips | MOTOR

A passion for training is what guides Ira Waldman and Tim Iezzi of Expertech as they lead technicians through lessons on lab scopes and diagnostic strategies. Iezzi told MOTOR, “I love seeing the lightbulbs go on in a student’s head. Teaching students to diagnose elevates them beyond parts changers, potentially improving their lives and those of others.” 

MOTOR: Why does a lab scope matter in modern automotive diagnostics? 

Expertech: A digital volt ohm meter (DVOM) averages voltage. That’s useful, but it hides the failure. A lab scope shows voltage over time, which is where modern problems live. In class, this shows up immediately with crank and cam sensors, injectors and CAN lines. With a scope, you can see momentary dropouts, missing teeth, double pulses, noise on grounds and voltage collapse under load. That’s the difference between guessing and knowing. In several examples, vehicles were diagnosed in minutes because the scope showed what the scan tool and meter could not. 

MOTOR: To help educate technicians, can you walk us through the process of setting up a lab scope to diagnose a misfire? 

Expertech: We start with a plan. Electrical, fuel or mechanical. Then pick tests that prove or eliminate each path. 

• Use the scan tool to identify the cylinder or system involved. 

• Scope ignition and injector current and command signals comparing to known good cylinders. 

• Perform a relative compression test to quickly rule in or out a mechanical problem. 

• Use an ignition sync so patterns can be matched to firing order. 

 

MOTOR: How can techs differentiate between a good and a faulty waveform? What are the key indicators? 

Expertech: Focus on five dimensions.  

• Amplitude: Is the signal reaching its expected voltage level? 

• Frequency: Does it change correctly with speed or load? 

• Shape: Clean edges versus rounded or distorted transitions. 

• Pulse width: Especially on injectors and PWM-controlled devices. 

• Pattern consistency: Repeating events should repeat evenly. 

Compare cylinders, compare before and after, and compare against known good examples. A bad pattern usually stands out once you know what “normal” looks like. 

MOTOR: What types of sensors and actuators can you evaluate with a lab scope? Can you provide tips for technicians? 

Expertech: Sensors, Actuators and Circuits I Scope Regularly 

• Crank and cam sensors
  Looking for correct amplitude, frequency, missing teeth and proper sync between cam and crank. Several cases showed good signals until load or heat exposed the fault. 

• Fuel injectors
  Both voltage and current patterns. I look for pintle movement, peak current, ramp shape and consistency across cylinders. 

• Ignition systems
  Primary current ramping to evaluate coil condition, module control and current limiting behavior.  

• CAN bus networks
  In order to evaluate data communication in a high-speed CAN bus we need to sample the communication at speeds that only a scope can achieve. We look for the waveforms to follow the rules of data communication, like dominant and recessive state voltages.  

• Fuel pumps and motors
  Use current patterns to evaluate motor condition and speed as well as other issues like restricted filters  

MOTOR: Let’s talk about some diagnostic scenarios and problem-solving issues. What about intermittent or no-code failures? 

Expertech: Intermittent and no-code failures are where scopes shine. Every fault code has code set criteria. Take a circuit short to ground fault. As an example, the circuit may have to fail for 50 milliseconds to set a fault code. 48 milliseconds do not set a fault code, but we can catch the failure before the car even knows it is broken and make that intermittent stand out.

MOTOR: How do you capture intermittent electrical faults? 

Expertech: Because a modern PC-based scope can record until your hard drive is full, we can record data until the vehicle breaks. Using advanced techniques like triggers and masks, we can make the scope stop and alert us when a failure has occurred.  

MOTOR: What mistakes should techs avoid? 

Expertech: 

• Using poor ground instead of battery negative. 

• Setting the voltage scale too low and the time base too small. 

• Over-filtering and smoothing out the very glitch you’re trying to find. Always verify ground integrity first.  

MOTOR: What are essential lab scope practices? 

Expertech: Inspect leads regularly, zero and calibrate current probes, and keep software updated so known good references are available. A bad lead can create a bad diagnosis. Test leads and probes get beat up and should be replaced on a regular basis.  

Choosing Time and Voltage Settings 

• High-speed signals like ignition, injectors and CAN require microseconds or milliseconds. 

• Slower signals like fuel pump current, temperature sensors, or voltage drop testing require seconds. 

• Voltage is always set slightly above expected maximum, so the signal isn’t clipped.

The rule is simple: see the overall trend first, then use the power of the scope to zoom in to see detail. 

MOTOR: In what ways can a technician explain vehicle repair problems to customers by referencing lab scope findings? 

In our shops, we rely heavily on visuals. Before-and-after screenshots tell the story faster than words. When customers can see the difference between a clean pattern and a failing one, trust goes up immediately. This approach is emphasized repeatedly in the training examples. 

MOTOR: Can you share some advice for new lab scope users? 

Expertech: Use the scope on good cars. It is almost impossible to learn on a broken car. If you do not know what good is you cannot know what bad is. At Expertech Automotive Training we challenge all our students to use their scopes after the class daily and capture good waveforms on working cars to gain comfort with the scope and build a database for when broken cars are in your bay.  

Ira, Tim and the entire Expertech team are very proficient with the scope, but they didn’t get there overnight, they put in the work testing good cars and still do. Technicians interested in learning more can visit the Expertech Facebook page or reach out to expertechtraining@gmail.com to be added to the email list. 

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