Skip to Content
Main Content

Your Guide to Snap-on® Functional Tests

An Introduction to Functional Tests

When it comes to diagnosing issues on modern vehicles, diagnostic tools play a pivotal role in unveiling the mysteries hidden beneath the hood. In this article, we'll delve into the Functional Tests feature within your tool.  

What are Functional Tests?

Functional Tests give you access to a list of  specific tests, procedures and/or resets, allowing you to quickly verify component operation.
Functional tests can be different, depending on the year, make and model of the vehicle (ex. power balance tests and output tests such as AC compressor clutch relay (on/off)). They can be relearns and resets, as well as EVAP service bay tests and much more. Depending on the OEM, functional tests can be available for engine, transmission, body control, anti-lock brakes, airbag and more modules.

These tests, also known as bi-directional controls, special functions, resets, relearns, coding, or even programming, serve to interact with the vehicle's systems to diagnose issues and perform specific tasks. Although terminology may vary between manufacturers, the purpose remains similar.

Snap-on® functional tests are best known for being very user-friendly. There is nothing worse than performing a functional test incorrectly because of a complicated procedure. These are all factory-level capabilities but are developed at Snap-on® with ease of use in mind.

Access Secure Functions

With newer vehicles, you are going to come across secured functions through secure vehicle gateways. Security Link™ provides technicians with access to OEM secure gateway functions directly from the scan tool further expanding the capabilities of your tool.

Security Link allows access to OEM secure gateway functions for the following vehicle manufacturers: 

  • FCA/Stellantis: for 2018+ vehicles need Gateway Access: Fiat®, Chrysler®,  Dodge®,  Jeep®, and RAM® 
  • Ford®: 2018+ need Gateway Functions for Some Secured Functions 
  • Nissan®: 2021+ need Gateway access for Some Secured Functions 
  • VAG: 2021+ need Gateway access for Some Secured Functions for Volkswagen®, Audi®, and Porsche® 



To find out more about Snap-on® Security Link™ and the functionality it brings to your tool with the latest Snap-on Software by clicking here.


Timesaving Example:

The Scenario: Customer complains the AC does not work. Upon initial inspection we see that the compressor is not engaged. There are potential issues. Performing the functional test below will help eliminate many of the causes. Selecting the ‘On’ button commands the AC compressor clutch to engage, when it does; and blows cold, we quickly learn what is not the problem and have a good direction to continue.



Next, we look at a functional test that will reset the Powertrain Control Module (PCM). In this scenario, we MUST perform the reset after the repair. We have replaced the oxygen sensor which has had amperage applied to heat it up quicker. Amperage climbs higher as sensors age. If we do not reset the PCM, it will continue applying a high rate of amperage to the new one. That will soon burn it out resulting in a comeback. Preventing that is priceless.



Other Functional Tests

Bi-Directional Controls

Bi-Directional Controls override control module outputs, this is useful when testing solenoids and relays. This is often used in diagnosis, typically when the vehicle’s computer shows a particular component is not working; however, we can use a functional test to command the computer to turn a relay on, this enables you to identify where the issue resides. Additionally functional tests can be used for verification after the replacement part has been installed, you can verify that the circuit is working correctly by turning the component on and off.

Some examples of this include:

•    Vent Valve on/off
•    A/C Clutch on/off

Special Tests

These may be a specific OEM test or scripted test, for example, a Compression Test or Power Balance Test where there are multiple steps required to verify a component or components are functioning correctly.


These procedures RESET a parameter back to factory specifications after the installation of a new component. Examples include resetting the Oxygen (O2) sensor, replacing engine oil, or changing the fuel filter. 


These are procedures to teach the Engine Control Module (ECM) to adapt to a new part. Whether it's a throttle body or valve body relearn or a Tire Pressure Monitoring System (TPMS) calibration, your Snap-on® diagnostic tool provides on-screen guidance. Before initiating the procedure, the system outlines the conditions that must be met before the procedure can begin to ensure an accurate and successful relearn procedure. 

To find out more about Snap-on® Service Resets and Relearn functionality and the added capability it brings to your tool, click here


Coding is used to TEACH the ECM parameters by using a code number, examples of this include: Fuel Injector Coding and Proxi Alignment, which is common on FCA Vehicles.


There is often a lot of confusion around this term in the Automotive Industry, but simply programming is used to CHANGE the ECM parameters based on a set list of parameters. An example of this using your Snap-on tool would be to select the vehicle's body control module and set it to unlock all doors with a single press or unlock just the driver's door, additionally, you can set the auto-lock time in seconds and program it into the module.

One thing in common

All functional tests have one thing in common: They save technicians a lot of time; both during the initial diagnostics and after the repair which prevents comebacks. Unlike PID data, Functional tests are typically bi-directional – they send a command from the scanner to a module/component then receives data back with the result.


Snap-on Functional Tests transform your vehicle diagnostics process. When paired with Snap-on Security Link, they grant you access to secured OEM functions right from your tool. These functional tests, include resets, relearns, and bi-directional controls, all of which save time on every job and ensure certainty in both diagnosing issues before replacing parts as well and post-repair verification, both reducing comebacks and enhancing customer satisfaction.

Functional Tests is a feature available on the latest Fast-Track® Intelligent Diagnostics products including the ZEUS®, TRITON® , APOLLO®, SOLUS® product families as well as MODIS® Edge and VERUS® Edge, ETHOS Edge and Vantage Ultra.


It pays to always have the latest software

If your car diagnostic tool is out of date because the software is old, working on cars will take longer and cost you money. You purchased the best diagnostic tool available, so you need to maintain it, so it is as good as the day you bought it and give you the confidence, you'll always be equipped to handle whatever vehicle comes into your workshop.

With each Snap-on Software release, we expand and incorporate new vehicle coverage. Additionally, you constantly have access to the latest testing resources, such as functional and actuator tests, bi-directional controls, resets and relearns, special tests, and more. The latest software ensures you always have the most comprehensive and up to date tool at your fingertips.


Learn more about the added capabilities the latest diagnostic software brings to your tool




Upgrade your Diagnostic Software


Diagnostic Software for Cars