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SESK: Stuff Everyone Should Know · sesk.info/cdl-low-air-warning

The low air pressure warning must come on before tank pressure drops below what?

55 psi.

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  1. 55 psi ✔
  2. 20 psi
  3. 100 psi

Why: A low air warning is required on air brake vehicles. It must come on before pressure falls below 55 psi, giving you time to stop while the brakes still work.

Huh, didn't know that: On large buses the warning commonly comes on at 80 to 85 psi.

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Why did the warning buzzer get a medal? It always spoke up at the right time.
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References

Answer: 55 psi. A low air warning is required on air brake vehicles. It must come on before pressure falls below 55 psi, giving you time to stop while the brakes still work.

  1. Texas Commercial Driver's License Manual (DPS) www.dps.texas.gov/internetforms/Forms/DL-7C.pdf
    The low air pressure warning signal must come on before the pressure drops to less than 55 psi in the air tank
    Checked 2026-10-10.

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