A serpentine belt tensioner can fail in two ways. These failures are common on all types of vehicles with serpentine belt tensioners, which is pretty much all modern cars and trucks. If your car has v-belts, then you most likely do not have a belt tensioner and if you have any chattering or squealing coming from your engine compartment, you will need to look at belt condition, pulley bearings on parts like the alternator, idler pulleys, water pumps, etc.
THE TWO TYPES OF TENSIONER FAILURES
TENSIONER BEARING FAILURE
When the belt tensioner bearing fails, the tensioner will squeal and shriek! If you ignore this squealing, the belt tensioner could eventually fly off! This takes a while, so if you’ve got some new squealing coming from the tensioner, then you’ve got some time to get it repaired. This type of tensioner failure is the hardest to diagnose, you will need a stethoscope like this one: Mechanics Stethoscope to listen to the bearings and identify the source of the squealing. You can also use the ear to long screwdriver method to identify the squeal, but that is not a preferred method.
TENSIONER SPRING FAILURE
When the belt tensioner spring fails the tensioner will chatter and jump This is a better failure to have since you can easily see the broken tensioner jumping around, the video below shows that type of spring failure. Eventually with a spring failure, you will probably have the belt jump off it’s pulleys if the car’s engine design allows, or the serpentine belt will jump around and rub and tear and fail. This type of belt tensioner failure should be addressed immediately.
REPLACING A BAD ENSIONER
A broken tensioner is not something to ignore. Use this opportunity to inspect the serpentine belt and replace if needed or replace as a preventive maintenance.
Usually replacing a bad belt tensioner is not too difficult and typically on most vehicles only requires common hand tools. Usually the only special tools that are sometimes a belt tensioner pry bar of some sort, some vehicles need a vehicle specific tool or prybar to remove the tension on the serpentine belt. Like this Honda Serpentine Belt Tool.
You can search for a replacement serpentine tensioner at Amazon.