If this is a sudden change, suspect a leak in one of the hydraulic systems. The red warning light should be on. If no leak is seen on the ground and the fluid level isn't going down in the reservoir, that leakage could be internal in the master cylinder. If this happened over a period of time it's more likely the rear drum brakes are worn down and have stopped self-adjusting. Either way, a brake inspection is called for.

Answered by caradiodoc (expert)
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