Advanced Engine Performance Specialist Test Turns 25

ASE’s Advanced Engine Performance Specialist (L1) Test is celebrating its 25th birthday this year. 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, according to officials.

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 onset, 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, according to the group.

“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,” said Tim Zilke, ASE President and CEO. “Our thanks are also due to the many industry professionals who have helped create and update this complex test over the years.”

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

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