Home › Practice › General Knowledge › Question 64
The most common reason for being placed out of service at a roadside inspection is:
Correct answer: B. Brake adjustment and brake systems
Why: Year after year, brake-related defects (out-of-adjustment slack adjusters and brake system violations) lead the FMCSA's out-of-service violation lists.
FMCSA requires General Knowledge competency under 49 CFR 383.111 because every CDL holder operates a heavy vehicle in mixed traffic where situational judgment, pre-trip discipline, and emergency response routinely separate a safe trip from a fatal one.
Read the FMCSA Model CDL Manual Section 2 cover to cover, then re-read it focused on numbers — speeds, distances, weights, and pressures. Use the practice questions in this category to drill those numeric thresholds until you can answer without hesitation.
The General Knowledge portion of the CDL knowledge exam covers more than this single question. Use this site's full General Knowledge bank to drill every topic, then test yourself with one of our state-specific practice sets to confirm you are ready for the actual DMV exam in your state. Always check your state's CDL handbook for any local addenda before the test day.
If you are still building your overall CDL foundation, start with the General Knowledge bank — every CDL applicant must pass it — and then work outward to the endorsements you plan to add.
