A weak tensioner can cause a variety of symptoms that may be difficult to diagnose. The most common symptom is an engine misfire, which results from the timing belt slipping off due to insufficient tension. Additionally, you may hear a loud squealing noise when starting your vehicle or accelerating, as the belt slips out of place due to lack of tension. You might also experience rattling noises coming from under the hood, which could indicate that the tensioner pulley has worn down and needs replacing. In extreme cases, the entire engine could shut down because it’s unable to maintain proper timing without adequate tensioning force being applied by the weak tensioner. It is important for all drivers to keep an eye on any signs of weakened performance in their car's engine so they can seek professional help should any issues arise as soon as possible before further damage can occur.