Which of the following defects of the transmission shall cause a vehicle to be taken out of service according to NFPA?

• A. Transmission lines or hoses that have persistent leakage or a fluid leak onto any exhaust system component
• B. A defective neutral safety switch
• C. Any transmission that does not operate in any of the selected gear settings
• D. Any automatic transmission which has a "do not shift" light illuminated

Answer: (D)

In NFPA’s out-of-service guidelines for fire apparatus, a safety-critical signaling issue from the transmission is a clear trigger to remove the vehicle from service. The "do not shift" light on an automatic transmission is a direct warning from the transmission control system that shifting is not safe. If that light is illuminated, the vehicle could shift unreliably or fail to shift when needed, creating a real risk during driving or emergency response. That direct, explicit warning makes it the single best indicator that the transmission defect is serious enough to take the vehicle out of service until repaired.

The other problems are serious and must be addressed, but they don’t carry that same explicit out-of-service signal in this context. A persistent leak onto an exhaust component is a fire hazard and needs repair; a defective neutral safety switch affects starting safety but isn’t an automatic out-of-service flag in this scenario; and a transmission that won’t operate in any gear setting is a severe mechanical failure but NFPA’s listed out-of-service criterion here centers on the illuminated warning indicating a fault that compromises safe operation.