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Combination Vehicles · Inspecting a Combination Vehicle

How does the manual say a driver should confirm that air has reached the rearmost trailer of a multiple-trailer combination?

1.Charge the system, open the shut-off valve on the emergency line at the rearmost trailer, and listen for escaping airCorrect answer
2.Check the tractor's own gauge only, since it reflects pressure throughout the entire length of the combination
3.Disconnect the last trailer in the line and then simply check whether it rolls freely enough on its own
4.Check that the ABS malfunction lamp on the very last trailer in line is lit up bright and steady

Explanation

Once normal air pressure is built and the trailer air supply knob is pushed in to charge the emergency lines, the manual sends the driver to the back of the rig to open the shut-off valve on the emergency line at the rearmost trailer; air escaping there proves the charge carried through every connection, and the service line gets the same treatment. This is manual-only procedure, topic-scoped to 49 CFR 383.111(c)(2). The tractor's own gauge reflects the tractor's reservoirs, not whether air has actually reached the last trailer through every connection. Disconnecting the last trailer to check free rolling tests something unrelated to whether air is actually flowing. An ABS malfunction lamp is an electronic fault indicator, not evidence about air pressure flow.

Source: 49 CFR 383.111(c)(2)

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