After connecting the air lines but before backing under the trailer you should:
Answer: B
Supply air to the trailer system, then pull out the air supply knob.
At this point, it is necessary to supply air to the trailer brake system by pulling out the air supply knob or moving the tractor protection valve control from the emergency to the normal position.
Source: Alabama CDL Manual
All choices
- AMake sure that the trailer brakes are off.
- BSupply air to the trailer system, then pull out the air supply knob.
- CWalk around the rig to be sure that is it clear.
Why the other answers are wrong
A. Make sure that the trailer brakes are off.
Trailer brakes are applied by supplying air, not turned off before backing under the trailer.
C. Walk around the rig to be sure that is it clear.
Walking around the rig is important but comes after supplying air to the trailer brake system.
Alabama CDL Combination Vehicles Test Info
Questions on Exam
20
Passing Score
80%
Time Limit
Typically 30 minutes; varies by testing location
Age Requirements
Intrastate: 18+ · Interstate: 21+
Alabama Law Enforcement Agency (ALEA)
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More CDL Combination Vehicles Practice Questions
- Glad hands are usually connecting which of these?
- Why should you lock the tractor glad hands to each other (or dummy couplers) when you are not towing a trailer?
- The crack-the-whip effect is related to:
- Sudden turns or aggressive braking will have the greatest effect on which trailer?
- Which task is NOT performed during the tractor protection valve test?