What does the tension pulley do?
A travel belt tensioner is a pulley mounted on a spring mechanism or adjustable pivot point that can be used to keep tension on the engine belts. … Both are used to keeptension on the engine serpentine belts so that they can drive the various engine accessories.

How do you adjust a tensioner pulley?
Convert the adjustment bolt on the side, top or bottom of the pulley counterclockwise with the ratchet and socket before item belt is loose enough to eliminate. Tighten the tensioner pulley by turning the adjustment bolt clockwise with the ratchet and socket until the belt is tight.
How do I know

A tensioner pulley manuals the belt around the tensioner and allows the belt to spin as the tensioner maintains pressure against it. A failing tensioner pulley could cause power loss and damage to your belt-driven devices. You might have a failing tensioner pulley if you hear any squeaking or squealing under the hood. Bearings on the pulley can degrade, causing noise and heating. Pulleys are usually manufactured from either plastic or metallic, so check the pulley itself for any damage as well. At O’Reilly Car Parts, we have tensioner pulleys available for many vehicle models.

The automated pulley tensioner comes with an internal spring-loaded mechanism that keeps the serpentine belt under constant tension. Its design allows it to keep the serpentine belt taut, so that the other accessory pulleys rotate at the same rpm (revolutions per minute) while beneath the same safe pressure. Tensioner pulleys may also absorb slight shock loads that happen when the air conditioning unit cuts on and off. As a regularly rotating element, the pulley tensioner can give off some warning signs before failure.

Rust and Corrosion
The pulley tensioner sits subjected to the elements at the front of the engine. Subjected to puddled water “splash-up,” with time the tensioner arm and pulley mechanism can rust. Corrosion can freeze the computerized tensioner device or rot the shaft bearings, that may cause a frozen job in the adjustment pressure. Without the correct stress, the belt can slip.
Debris Contamination
Rocks, gravel and other street debris can be thrown up into the tensioner pulley grooves and jam the mechanism. This can permit the serpentine belt to slip on the tensioner pulley and shed. Overheated pulley temp results, and finally the serpentine belt will melt and snap off.
Pulley Tensioner Spring
The pulley tensioner spring inside housing may become weak from age and repeated exposure to heat. This causes the belt to flutter and skip instead of maintaining a constant strain on the pulley. Symptoms of a fragile spring show as glazing on the underside of the serpentine belt, with an occasional flickering of the dashboard’s charging lumination indicator. Squealing or squeaking will always be read at the belt position.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, it means the interior shaft bearings have worn. This will cause a pulley misalignment. Awful bearings trigger an audible growling sound. The external ends of the serpentine belt will fray and extend the belt. At some point the rubber belt grooves flatten out and cause important slippage. An excessively wobbling pulley can throw the belt off, causing all the components to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys possess markings on the casing that indicate the maximum selection that the pulley can travel. If the lever arm of the tensioner rides under or over the designated mark, it indicates a stretched belt or a lever arm which has jammed in a single position.
Pulley Misaligment
The tensioner pulley face must match up to the other accessory pulleys with a parallel alignment. Placing an extended, straightedge ruler against the facial skin of the tensioner pulley, and then flushing it against another equipment pulley, can measure the angle. Any off-position measurement indicates put on shaft bearings in the pulley housing.
Serpentine Belt Noise
A moderately worn serpentine belt produces a constant squeaking noise during engine idle. Belts which have worn severely task a loud chirping or squealing sound. The cause items to a glazed, worn or cracked belt. Dry or partially frozen tensioner pulley bearings could cause such sounds by deteriorating the belt prematurely.
Lever Arm Oscillation
A lever arm that repeatedly oscillates back and forth during idle or more speeds means the the within damper mechanism in the tensioner pulley has weakened or broken. This causes sporadic tension strain on the belt and will manifest itself with intermittent chirping noises.