The timing belt tensioner is what applies pressure to the timing belt, keeping it tight and running smoothly. When something goes wrong, it is often the tensioner that’s the cause and not the timing belt itself. To prevent the timing belt from failing, the timing belt, tensioner and idler pulleys should be replaced every 50 to 70,000 miles.
Be sure to ask your service advisor about your recommended service interval. If the tensioner breaks, the timing belt can slip or break. The split-second synchronization of engine parts would then be lost and the damage could be catastrophic. A broken timing belt can cause the pistons to collide with the valves, potentially bending or breaking them.
From a safety standpoint there is a slight risk. If your car breaks down, you could end up stranded. There is no environmental impact from timing belt tensioner replacement.