The Nissan Frontier uses a serpentine belt to provide power to the engine accessories. In order for a single belt to power all components, it must run in a "serpentine" fashion. Idler pulleys are used to direct the belt when a redirection is required. You might need to replace an idler pulley if it becomes warped or if a crack develops. Four-cylinder engines use two idler pulleys to route the belt while the six-cylinder only uses one pulley.
Remove the cover from the top of the engine by removing the two bolts located near the front of the cover. Use a socket wrench to turn the bolts counterclockwise to remove them. Locate the belt routing diagram, either on the underside of the hood or on the top of the grille near the hood latch. If the diagram is missing, sketch out your own diagram before removing the belt.
Detach the harness connector from the upper air cleaner assembly. The air cleaner has attachment points where the wiring harness runs along it.
Remove the three clips from the upper part of the air cleaner. Follow the air duct to the resonator. This is the flat object about halfway down the air duct. Remove the single bolt that attaches it to the vehicle. Loosen the hose clamp on the far end of the air duct. Remove the air duct, resonator and upper part of the air duct assembly as one unit. It isn't necessary to separate these components.
Unscrew the two bolts that connect the lower part of the air cleaner to the vehicle then remove the air cleaner.
Insert an idler pulley tool into the auto tensioner and rotate it counterclockwise to relieve tension on the belt. Slip the serpentine belt off the auto tensioner pulley while maintaining pressure on the pulley with the tool. The auto tensioner pulley is located directly to the right of the power steering oil pump pulley. Continue to remove the belt from all the pulleys then set it aside. If you don't have the special tool, you can use any similarly-shaped tool that will fit into the auto tensioner.
Locate the idler pulley. On the four-cylinder engine, there are two idler pulleys. One is located between the power steering and water pump pulleys. The second is located directly beneath the first. On six-cylinder engines, there is a single idler pulley, which is the uppermost pulley. Remove the bolt from the center of the pulley and detach the pulley. Attach the new idler pulley, tightening the bolt to 26 ft.-lbs. with a torque wrench.
Replace the serpentine belt, making sure to follow the correct path through the pulleys. Rotate the auto tensioner as you did in Step 5 and slip the belt over the auto tensioner pulley. Release pressure on the tool and remove it.
Reattach the lower portion of the air cleaner assembly and replace the two attaching bolts. Replace the air duct, resonator and upper part of the air cleaner assembly. Tighten the clamp on the air duct, replace the single bolt in the resonator and reattach the upper portion of the air cleaner to the lower portion with the three plastic clips.
Insert the wiring harness back into the clips along the upper part of the air cleaner. Replace the engine cover and reinsert the two bolts.
