One problem related to engine belts and pulleys has been reported for the 2004 Nissan Frontier. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2004 Nissan Frontier based on all problems reported for the 2004 Frontier.
2009 started hearing knocking noice from engine. Seem to come and go. Took it to Nissan and discovered the crank pulley was coming apart. Year and half later belts were squealing. Took truck in for tires and asked them to check the belts. Discovered the idler pulley was coming apart. Was informed by service people at tire dealer( tires plus) they have seen this before on Nissan vehicles with the same engine. This was in 2011. Two bad pulleys with less than 42,000 miles on truck. No telling what would have happened if either of this pulleys had come apart at highway speeds. Have never heard of pulleys coming apart on a vehilce before.