To remove the air brake restriction from your CDL in Michigan, you have to pass the air brake knowledge test at a Secretary of State office and the air brake skills test with an approved third-party Driver Testing Business, using a vehicle equipped with air brakes. Once both are done, the Secretary of State treats the change as a new CDL issuance and reprints your license without the “L” code.
Why the “L” Restriction Matters
Federal rules require every state to mark a CDL with a code showing it isn’t valid for vehicles with air brakes whenever the driver hasn’t passed the air brake knowledge test or took the skills test in a vehicle without air brakes.1eCFR. 49 CFR 383.95 – Restriction on CMVs With Air Brakes Michigan mirrors that rule, and the restriction stays until you pass both the knowledge and skills tests.2Michigan Legislature. Michigan Code 257.312e – Operation of Commercial Motor Vehicle
Most commercial trucks and buses run on air brakes, so a CDL carrying the “L” closes off most of the work. Michigan law puts it plainly: a holder with the restriction “shall not operate a commercial motor vehicle equipped with air brakes.”2Michigan Legislature. Michigan Code 257.312e – Operation of Commercial Motor Vehicle Driving one anyway can mean fines, an out-of-service order, and CDL suspension.
What You Need Before You Test
You already hold a CDL, so most of the baseline work is behind you. A few items still need to be in order:
- A current Medical Examiner’s Certificate from an examiner on the FMCSA National Registry, which you must carry while driving.3eCFR. 49 CFR Part 391 – Qualifications of Drivers
- Your valid Michigan CDL, Social Security card, and two documents proving Michigan residency.
- A CDL application listing your driving history across all states for the past ten years.4Michigan Department of State. Applying for a Commercial Driver’s License (CDL)
One point worth flagging because it trips people up: entry-level driver training is not required when you’re removing the air brake restriction from an existing CDL. The FMCSA has specifically exempted restriction removals from the ELDT requirement.5Training Provider Registry. Frequently Asked Questions ELDT only applies if you’re getting a brand-new CDL and want it issued without the restriction in the first place.4Michigan Department of State. Applying for a Commercial Driver’s License (CDL)
The Knowledge Test
You take the written exam at a Michigan Secretary of State branch office on a computer testing station. It runs 25 questions and follows the federal content standards in 49 CFR Part 383.4Michigan Department of State. Applying for a Commercial Driver’s License (CDL)2Michigan Legislature. Michigan Code 257.312e – Operation of Commercial Motor Vehicle
Section 5 of the Michigan CDL Manual is the study source. Expect questions on the air compressor and governor, air storage tanks, dual air brake systems (separate circuits for front and rear so one failure doesn’t take out all stopping power), and why draining tanks matters for keeping moisture and corrosion out of the lines. Know the governor’s working range: cut-out around 125 psi, cut-in around 100 psi.6Michigan Department of State. Michigan Commercial Driver’s License Manual – Section 5 Air Brakes
The Skills Test
The skills test is not administered by the Secretary of State. You schedule it with an approved Driver Testing Business through the Michigan Department of State’s online locator tool, at least two days before your intended test date. The vehicle you bring must be equipped with air brakes. If it isn’t, the “L” stays on your license no matter how you perform.4Michigan Department of State. Applying for a Commercial Driver’s License (CDL)
If you don’t own a qualifying vehicle, some testing businesses rent one. Rental fees can run $250 or more on top of the test fee.
The Pressure Checks You Have to Demonstrate
Know the target numbers cold. The examiner walks you through a sequence of checks on the air system:
- Governor check. With the engine running, build pressure until the governor cuts the compressor out, which should happen around 125 psi. Fan the brake pedal to drop pressure and confirm the governor cuts the compressor back in around 100 psi. Federal regulations set the outer limits at 80 psi for cut-in and 135 psi for cut-out, though most vehicles sit inside the tighter manual range.7eCFR. 49 CFR 570.57 – Air Brake System
- Low-pressure warning. As you keep bleeding pressure, the warning light or buzzer must activate before pressure drops below 60 psi.6Michigan Department of State. Michigan Commercial Driver’s License Manual – Section 5 Air Brakes
- Spring brake check. Keep lowering pressure and the parking brake valves should pop out, engaging the spring brakes automatically. This typically happens between 20 and 45 psi.
- Static air leak check. Engine off, brakes released, watch the gauge for one minute. Federal standards allow no more than a 2 psi drop per minute on a single vehicle, or 3 psi per minute on a combination.7eCFR. 49 CFR 570.57 – Air Brake System
Fees and Getting the New License
Michigan charges $18 for a new photo license ($33 for an enhanced license) plus a $9 correction fee to remove the restriction. The state processes it as a new CDL issuance for fee purposes.4Michigan Department of State. Applying for a Commercial Driver’s License (CDL) Skills test fees paid to the third-party testing business are separate and vary, but figure around $150 per attempt.
Once the Secretary of State office processes the change, you walk out with a temporary paper document confirming the restriction is gone. The permanent card arrives by mail, typically in two to three weeks. Keep the temporary paperwork on you until the plastic shows up. That paper is your proof you can legally operate air-brake-equipped vehicles.