What is the function of a timing belt tensioner, and what operational symptoms indicate it may be failing?

What is the function of a timing belt tensioner, and what operational symptoms indicate it may be failing?

• A. Controls ignition timing with no relation to belt tension.
• B. Maintains proper belt tension; symptoms: squealing, belt slipping, intermittent timing, unusual engine noise, mis-timing.
• C. Tensions the belt when the engine is cold to prevent warping.
• D. Adjusts valve lash automatically.

Answer: (B)