On a combination vehicle, does the low air pressure warning respond to pressure in the trailer's air tanks as well as the tractor's?

Pick an answer

1. The trailer has a completely separate warning system the tractor driver never sees or hears, wired independently from the cab
2. Trailers never have any effect on the tractor's air pressure readings under any condition
3. The warning only tracks trailer pressure and ignores the tractor's own tanks entirely
4. The warning is built around the tractor's own air system, which is what actually supplies and monitors the trailer's brakes through the shared lines

Correct!

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