Which CDL Knowledge Tests Do You Need? Tests by Class and Endorsement

General Knowledge: the CDL test every class shares

Whatever class you want, the list starts with General Knowledge. Federal rules require you to pass a general knowledge test for your vehicle group before a state can issue you a commercial learner's permit (49 CFR 383.71(a)(2)). The content is the same 20 federal areas for Class A, B and C applicants (383.111(a)).

From there, three things decide the rest of your list:

• Your vehicle group. Class A is for combinations rated 26,001 lb or more whose towed unit is rated over 10,000 lb, Class B for single vehicles rated 26,001 lb or more, Class C for smaller vehicles designed for 16 or more people, including the driver, or used to haul placarded hazardous materials. The Class A, B and C guide works through the weight ratings.
• Your vehicle's brakes. Air brakes, including air over hydraulic systems, bring in the Air Brakes test.
• The work you plan to do. Passengers, tanks, hazardous materials, double or triple trailers and school buses each have an endorsement with its own test.

A decision table for the CDL knowledge tests you need

Find the row closest to the vehicle and job you are training for. The tests listed are the federal ones for that combination, and your state may add others.

Two notes on the table. A Class A license also covers Class B and C vehicles, and a Class B covers Class C, as long as you hold the endorsements the vehicle needs (383.91(c)). And if you are not sure whether your vehicle has air brakes, Washington's CDL guide notes that the Air Brakes test applies to air over hydraulic systems too, so ask your employer or school before you skip it.

Air Brakes: skipping or failing it restricts your CDL

Federal rules put an air brake restriction on a permit or license in two cases: you fail the air brake knowledge test, or you take the skills test in a vehicle without air brakes (383.95(a)). For this rule, "air brakes" means any system that works fully or partly on air (383.95(a)(2)). The restriction appears as code L, "No Air brake equipped CMV" (383.153). If you never pass the Air Brakes test, expect the restriction as well: removing an L later requires passing the air brake knowledge test (383.135(b)(7)).

A related code covers air over hydraulic brakes. If you take the skills test in a vehicle with air over hydraulic brakes, the license is restricted from vehicles with full air brakes, code Z (383.95(b)). The air brake restrictions guide explains how each code is removed. Passing Air Brakes the first time is the simpler route, and 207 Air Brakes questions with 70 flashcards are planned for full CDL prep.

Combination Vehicles: no pass, no Class A permit

The Combination Vehicles test gates Class A. If you score below 80% on it, the state must not issue you a Group A permit or license (383.135(a)(3)). The test covers three federal areas: coupling and uncoupling, inspecting combination vehicles, and operating practices including trailer air brakes (383.111(c)).

Because trailer air brakes appear in that list, Class A applicants whose rig has air brakes usually study the two tests together. The Combination test still has to be passed on its own, with its own 80%, which is why the CDL prep planned for launch tracks Combination Vehicles accuracy apart from Air Brakes.

Endorsement tests: which are knowledge-only

Each endorsement has its own knowledge test, and two of them also need a skills test (383.93(c)). Only three can go on a learner's permit (383.25(a)(5)).

On a learner's permit, "no passengers" means no one aboard except auditors, inspectors, test examiners, other trainees and the accompanying CDL holder (383.25(a)(5)). A tank counts for the N endorsement when it has an individual rated capacity over 119 gallons and an aggregate of 1,000 gallons or more (383.5). The endorsements guide covers each endorsement in more depth, including the training rules, and all five endorsement tests have their own question sets in the CDL prep planned for launch.

How states add to the federal CDL test list

The federal list is a floor, and states run the tests their own way. Three examples show the range:

• Texas adds a test. As of October 2026, per Texas DPS, applicants take the knowledge tests in this order: Texas Commercial Rules, General Knowledge, Combination (Class A only), Air Brake (if applicable), then endorsements.
• Florida spells out the Class A list. As of October 2026, per FLHSMV, Class A applicants take General Knowledge, Combination Vehicles and, if applicable, Air Brakes, noting that most Class A vehicles have air brakes but not all.
• Washington publishes its counts. As checked on October 28, 2026, General Knowledge has 50 questions (40 to pass), Combination 20 (16), and Air Brakes 25 (20).

Question counts, fees and retest rules belong to your state, and the format and passing score guide compares a few. Check your state's CDL manual for its list before you book.

Once your list is settled, try the 20 free CDL practice questions and see how your answers split across the three core tests. The free set covers General Knowledge, Air Brakes and Combination Vehicles, with no endorsement questions.