3 Tools Pros Use to Make an Accurate Diagnosis

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Professional Auto Tech

When it comes to diagnosing your car, honest professional automotive technicians can’t afford to be wrong. On Board Diagnostic Systems are extremely helpful in determining where to begin an accurate diagnosis, but relying on code descriptions alone can lead to an incorrect diagnosis, accompanied by unnecessary component replacement.

That is why skilled and knowledgeable techs and shop owners are equipped with specific component testing tools and equipment, which leave nothing to chance. By purchasing, and using these three tools, you too can perform an accurate diagnosis.


Digital Volt/Ohm Meter (DVOM)

Even if you own or have access to a scanner, live data is necessary for making an accurate diagnosis. Data displayed on a scanner is delayed by as much as three-seconds; if you are to locate a momentary glitch in a throttle-position-sensor or pin-point an intermittently shorting solenoid, then you need live data.

A DVOM, placed in the precise location, will provide you with live data, as it is occurring. This can enable you to detect a faulty electrical connection inside of a sealed engine management sensor or observe a solenoid as it creates excessive resistance in a particular circuit.

By following wiring diagrams and diagnostic trouble code flow charts you can accurately diagnose your vehicle’s service engine light quickly and effectively.


vacuum pump
Hand Vacuum Pump

This is an inexpensive and easy to use tool that any technician must have. It allows you to test vacuum operated components and circuits by applying the specified amount of vacuum, manually. Exhaust Gas Recirculation (EGR) trouble codes are very common in light and medium-duty vehicles.

With the vacuum operated EGR system component list numbering six to ten, an accurate diagnosis can be challenging, despite the fact that you have a trouble code in hand. Typical EGR activation protocols can include various vehicle speed parameters, which cannot be met while parked in the driveway. By using the hand-actuated vacuum pump, you are able to apply precise vacuum to various points of the EGR system. This allows you to isolate individual components, such as the EGR valve (rarely the cause of an EGR related code), EGR control solenoids, sensors, filters, and intake ports. Used in conjunction with the DVOM, this time tested tool can pay for itself in just one usage.


smoke machine
Smoke Machine

It doesn’t cook burgers and dogs, but this machine will save you hours and hours if you perform regular diagnostic procedures. With evaporative emission (EVAP) codes being some the most common causes of customer complaint, the pros know that a smoke machine is indispensible. Late model EVAP systems require yards of multiple plastic and rubber vacuum lines, which must extend from the underhood area to above the fuel tank. These lines and hoses are frequently burned, cut, or damaged resulting in an EVAP code and an ensuing service engine soon (SES) light.

Using the smoke machine, the technician has the ability to fill these lines with smoke which will then become visible wherever a leak is present. Tiny cracks, which are difficult to spot visually, become obvious when harmless white smoke is spewing from them. The smoke machine can be a bit expensive but quickly pays for itself in time-saved.


S.M. Darby

S.M. Darby

I am a freelance author with over 25 years of experience as a professional, ASE certified automotive technician and shop owner, muscle car enthusiast, avid street racer, and classic car restoration specialist.