CDL General Knowledge TestCombination Vehicles (if applicable)Medium
What is the primary reason for performing a 'tug test' after coupling a tractor to a semi-trailer?
- ATo check the air brake system's pressure retention.
- BTo verify the electrical connection between the tractor and trailer.
- CTo ensure the fifth wheel jaws have securely locked onto the kingpin.
- DTo adjust the landing gear for proper trailer level.
Show answer & explanationAnswer & explanation
Correct answer: C. To ensure the fifth wheel jaws have securely locked onto the kingpin.
The tug test is a crucial safety check to confirm that the fifth wheel jaws have properly closed around the kingpin. This prevents accidental uncoupling during operation.
Why the other options are wrong
- A. Air brake pressure retention is checked separately, not by the tug test.
- B. Electrical connection is checked by testing lights and signals, not by the tug test.
- D. Landing gear adjustment is done before coupling and after uncoupling, not during the tug test.
Tug Test Purpose
The tug test confirms the secure mechanical connection between the tractor's fifth wheel and the trailer's kingpin.
- Performed after coupling.
- Verifies fifth wheel jaws are locked.
- Prevents accidental uncoupling.
- Involves gently pulling forward.
Memory trick: Lock and Tug for a secure hug.