What does the tension pulley do?
A travel belt tensioner is a pulley mounted on a spring system or adjustable pivot point that is employed 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 modify a tensioner pulley?
Transform the adjustment bolt on the side, top or bottom of the pulley counterclockwise with the ratchet and socket until the equipment 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 courses the belt around the tensioner and allows the belt to spin while the tensioner maintains pressure against it. A failing tensioner pulley can cause power reduction and damage to your belt-driven devices. You may have a failing tensioner pulley if you hear any squeaking or squealing under the hood. Bearings on the pulley can wear out, causing noise and high temperature. Pulleys are usually manufactured from either plastic or steel, so examine the pulley itself for just about any damage aswell. At O’Reilly Auto Parts, we have tensioner pulleys available for many vehicle models.

The computerized pulley tensioner has an internal spring-loaded mechanism that keeps the serpentine belt under frequent tension. Its design enables it to keep the serpentine belt taut, in order that the other equipment pulleys rotate at the same rpm (revolutions per minute) while beneath the same safe pressure. Tensioner pulleys can also absorb mild shock loads that happen when the air conditioner cuts on and off. As a regularly rotating part, 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 system can rust. Corrosion can freeze the automated tensioner device or rot the shaft bearings, which will cause a frozen position in the adjustment pressure. Without the proper tension, the belt can slip.
Debris Contamination
Rocks, gravel and other road debris can be thrown up into the tensioner pulley grooves and jam the system. This can permit the serpentine belt to slide on the tensioner pulley and burn off. Overheated pulley heat results, and eventually the serpentine belt will melt and snap off.
Pulley Tensioner Spring
The pulley tensioner spring in the housing can become weak from age and repeated contact with heat. This triggers the belt to flutter and skip rather than maintaining a constant pressure on the pulley. Symptoms of a weak spring demonstrate as glazing on the lower of the serpentine belt, with an intermittent flickering of the dashboard’s charging light indicator. Squealing or squeaking will be heard at the belt location.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, it means the inside shaft bearings have worn. This will cause a pulley misalignment. Poor bearings trigger an audible growling noise. The outer ends of the serpentine belt will fray and stretch the belt. Eventually the rubber belt grooves flatten out and cause significant slippage. An excessively wobbling pulley can throw the belt off, creating all the equipment to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys have markings on the housing that indicate the maximum range 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 one 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 item pulley, can measure the angle. Any off-angle measurement indicates donned shaft bearings in the pulley housing.
Serpentine Belt Noise
A moderately donned serpentine belt gives off a constant squeaking sound during engine idle. Belts that have worn severely project a loud chirping or squealing sound. The cause details to a glazed, put on or cracked belt. Dried out or partially frozen tensioner pulley bearings can cause such sounds by deteriorating the belt prematurely.
Lever Arm Oscillation
A lever arm that repeatedly oscillates backwards and forwards during idle or more speeds means the the inside damper mechanism in the tensioner pulley has weakened or broken. This causes sporadic tension strain on the belt and can manifest itself with intermittent chirping sounds.