ASE: Advanced Engine Performance Specialist Test (L1) turns 25


LEESBURG, Virginia, April 8, 2019 – ASE’s Advanced Engine Performance Specialist (L1) Test is celebrating its 25th birthday in 2019. By the end of this year, 100,000 service professionals will have earned the L1 credential since its inception. Combining complicated generic questions with others requiring use of a Composite Vehicle reference booklet, the L1 test is the highest ASE credential a driveability and emissions technician can achieve.

In the early 1990s, the industry asked ASE for a certification test to address the enhanced I/M emissions initiatives of that time. The Advanced Engine Performance Specialist (L1) Test answered that call by measuring the knowledge needed to diagnose emission failures and driveability problems on computer-controlled engine systems. From the outset, L1 set the standard for evaluation of technicians’ abilities to research system operation, correlate it with exhibited symptoms, and come to a conclusion on the source of the problem.

“Those who have achieved the Advanced Engine Performance Specialist (L1) credential are among the most accomplished people in our industry, past and present, and we are proud to have them as part of the ASE family,”  “Our thanks are also due to the many industry professionals who have helped create and update this complex test over the years.”

— Tim Zilke, ASE President & CEO

The Advanced Engine Performance Specialist Test was ASE’s first Advanced Level test, challenging technicians to be at the top of their game. It was also the first to require the development of a “model” Composite Vehicle detailed in a supplemental reference booklet for in-test use. The Composite Vehicle has a generic powertrain control system representing a cross section of computerized engine control technology, developed to ensure test accuracy without bias towards any single manufacturer or application.


The test has been regularly updated to reflect advances in technology and currently uses Composite Vehicle Type 4, released in 2016. The reference booklet is now 36 pages with a four-page wiring schematic and can be seen at

The National Institute for Automotive Service Excellence (ASE) was established in 1972 as a non-profit organization to help improve the quality of automotive service and repair through the voluntary testing and certification of automotive technicians and parts specialists. Today, there are approximately a quarter of a million ASE Certified professionals at work in dealerships, independent shops, collision repair shops, auto parts stores, fleets, schools and colleges throughout the country. For more information about ASE, visit