Air Brakes and Acronyms at the DMV
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Article by Christoff Barfield, Gardena CDTC Manager
Acronyms are a particular specialty of the CA DMV – or California Department of Motor Vehicles, to be exact.
When it comes to prospective commercial drivers, the most important acronym might be C-O-L-A-S, which corresponds to the five segments of the air brakes check portion of the vehicle inspection. This is one of the most challenging aspects of the entire Commercial Driver License Skills Test, as it requires applicants to both verbalize knowledge of acceptable testing parameters while physically performing and verbalizing the results of an inspection of the air brake system on their vehicle.
Because of its critical nature to the skills test, the DMV wants to highlight the different segments of the air brakes check, as well as some common errors.
C is for Cut In: This test identifies the point at which the governor allows the compressor to build up air pressure after repeated use of the brakes, avoiding dangerously low pressure. This is checked by slowly depleting air through application of the brake, and watching when the governor "cuts in" and the air gauge needle begins to rise. A common mistake is rapidly fanning the brake without waiting between pumps, making it impossible to determine when the Cut In actually occurred.
O is for Cut Out: This test measures the maximum air pressure before the governor stops supplying air, avoiding uncontrolled pressure buildup. The goal is to identify when the needle stops rising, indicating that Cut Out has occurred. Common errors include attempting to perform the test while the needle is already stationary, or indicating that Cut Out has occurred because the sound from the air dryer (spitter valve) is heard.
L is for Low Air Warning: All vehicles with air brakes must be equipped with a low air warning device – an audible alarm, a light, or both – to alert the driver of low air pressure. This test causes the low air warning to activate through repeated application of the brake, and identifies the pounds per square inch (PSI) at which this occurs. Common mistakes include not having the ignition key in the "on" position, or continuing to fan the brake after the warning has activated.
A is for Applied Leakage Test: This checks for air loss during a one-minute period of continuous brake application, which would alert the driver of a dangerous leak. Common errors include not waiting to let the air pressure gauge "settle" before beginning the timed session, failing to release all parking brakes or not having sufficient air pressure before starting the test, and leaving the motor running.
S is for Spring Brakes: These act as emergency brakes on air brakes-equipped vehicles, and activate automatically when air pressure reaches dangerously low levels. Also referred to as a "pop out" test, this determines what PSI the spring brakes will activate after depleting the air pressure by fanning the brakes continuously. A common mistake includes not releasing the parking brakes prior to starting the test.
It is important to note that for all of the C-O-L-A-S segments, it is the applicant’s responsibility to not only physically perform the test and note the results to the DMV examiner, but also to verbalize the acceptable parameters for each test as indicated in Chapter 5 of the California Commercial Driver Handbook. Failure to verbalize the correct parameters is one of the most common reasons drivers fail the air brakes check.
Remember, this all takes place in the same vehicle the applicant brings to the test. All vehicles are different, and the one being tested might have different settings than the one on which the applicant practiced.
It is also important to note the order of the tests is entirely up to the applicant. This article addressed the tests in the same order of the acronym, but they do not have to be performed in that sequence. C-O-L-A-S could just as easily be L-O-C-A-S. However you want to do it, good luck and safe driving!
Article provided by the California Department of Motor Vehicles. The views expressed in this article reflect the views of the author and do not necessarily reflect the views of the California Trucking Association.
