CDL ExamStudy Topic
General Knowledge for the CDL Exam
Study general knowledge for your CDL exam. Covers vehicle inspection, basic vehicle control, CLP rules, medical certification, and disqualifying offenses.
Topic Overview
The general knowledge test draws on the topic areas required by 49 CFR Part 383, Subpart G. Every CDL applicant must pass this test before moving on to any class-specific or endorsement-specific knowledge test. While the exact question count varies by state (most states use 50 questions, Illinois uses 30, and Pennsylvania uses 70 for Class A and 50 for Class B or C), the federal passing score is 80 percent on every knowledge test, general knowledge included.
Vehicle inspection is one of the most heavily tested areas. Drivers must be able to perform a pre-trip inspection covering the engine compartment, cab, lights and reflectors, mirrors, steering, suspension, brakes, tires and wheels, coupling devices (if applicable), and the cargo area. Knowing the purpose of each inspection step, not just the checklist order, is what the exam actually tests.
Basic vehicle control systems covered include the accelerator, clutch (on manual transmissions), steering, mirrors, and retarders. Candidates should understand how to control speed on grades, how to steer to avoid a crash (rather than braking hard, which can cause a skid or jackknife on some vehicle types), and how backing and turning differ for larger commercial vehicles compared to passenger cars.
Driver qualifications tested include the Commercial Learner's Permit (CLP) process, medical certification requirements, and the disqualifying offenses that can end a CDL. A CLP holder must be at least 18 years old, must pass the general knowledge test (and any endorsement knowledge test for the only endorsements permitted on a CLP, which are P, S, and N), and must wait at least 14 days from CLP issuance before taking the CDL skills test. CLP holders cannot transport hazardous materials under any circumstances. Medical certification requires examination by a provider listed on FMCSA's National Registry of Certified Medical Examiners; letting a medical certificate lapse triggers a downgrade of CDL privileges, but does not by itself void the CDL card's own expiration date.
Disqualifying offenses are also tested. The blood alcohol concentration (BAC) threshold for a CDL holder operating a commercial motor vehicle is 0.04, half the 0.08 threshold used for non-commercial driving. A first-offense major violation (such as DUI, refusal to test, or leaving the scene of an accident) results in a 1-year disqualification, or 3 years if the driver was hauling placarded hazardous materials at the time. A second offense of any combination of these major violations results in a lifetime disqualification. Federal rules also ban texting and hand-held phone use while operating a commercial motor vehicle.
Since June 25, 2025, enforcement of the existing English Language Proficiency requirement has changed: a driver who cannot demonstrate sufficient English proficiency during a roadside inspection can now be placed out of service. The underlying rule requiring drivers to read and speak English sufficiently is not new, but the enforcement consequence is.
- Assuming the general knowledge test has the same number of questions in every state; the 80 percent passing score is a federal minimum, but the question count varies (most states use 50, Illinois uses 30, Pennsylvania uses 70 for Class A and 50 for Class B/C).
- Believing the BAC limit for a CDL holder is 0.08, the same as a regular license; it is 0.04 while operating a commercial motor vehicle.
- Assuming a DUI only counts against your CDL if it happened while driving a commercial vehicle; a DUI conviction in a personal vehicle can still trigger a federal CDL disqualification.
- Confusing the 14-day CLP holding period (the minimum wait before you can take the skills test) with CLP validity (up to one year from issuance, though some states issue it for a shorter term such as 180 days within that ceiling).
- Assuming a lapsed medical certificate immediately voids the CDL; it triggers a downgrade of driving privileges after a grace period, but the CDL card's own multi-year expiration date is a separate matter.
- Thinking ELDT applies to every CDL applicant with no exceptions; drivers who already held a valid CDL, or the S/P/H endorsement, before February 7, 2022 are grandfathered and exempt.
Checkpoint Quiz
Test your understanding of General Knowledge
These questions are for study practice only and are not official exam questions.
1. What is the minimum age to obtain a Commercial Learner's Permit under federal rules?
2. A driver is convicted of a DUI while operating their personal vehicle, not a commercial motor vehicle. Does this affect their CDL?
3. A driver holding only a CLP is asked to haul a load containing hazardous materials. What is the correct response?
4. What blood alcohol concentration (BAC) is the disqualifying threshold for a driver operating a commercial motor vehicle under federal rules?
5. What is the purpose of using turn signals well before a turn or lane change?
6. What should a driver do with headlights when driving at night to reduce risk?
7. What is a common effect of driver fatigue?
8. What does the 'X' endorsement on a CDL represent?
9. What does restriction code 'K' mean on a CDL?
10. What does the 'P' endorsement on a CDL allow?
Frequently asked questions
Who has to take the CDL general knowledge test?
Every CDL applicant must pass the general knowledge test, regardless of which class (A, B, or C) or endorsement they are pursuing. It is the foundational knowledge test required before any class-specific or endorsement-specific test.
How many questions are on the general knowledge test?
The question count is not set by federal regulation and varies by state. Most states use 50 questions, but Illinois uses 30 and Pennsylvania uses 70 for Class A (50 for Class B or C). The federal passing score of 80 percent applies in every state. Confirm the exact format with your state's current CDL manual.
What topics does the pre-trip vehicle inspection portion cover?
It covers the engine compartment, cab, lights and reflectors, mirrors, steering, suspension, brakes, tires and wheels, coupling devices where applicable, and the cargo area. The exam tests whether you understand the purpose of each check, not just memorized checklist order.
What is a Commercial Learner's Permit (CLP) and how long must I hold it?
A CLP allows behind-the-wheel training when accompanied at all times by a properly licensed CDL holder. You must be at least 18, pass the general knowledge test (and any endorsement test for P, S, or N, the only endorsements allowed on a CLP), and wait a minimum of 14 days after CLP issuance before taking the CDL skills test. A CLP is valid for no more than one year from initial issuance.
