2000 Nissan Frontier Engine hesitation on warm-up

Engine hesitates on warm-up (temp gauge moves into normal reading) and runs normal when cools down until it warms up again. Replaced spark plugs, rotor/cap, and fuel filter. Spark plugs were certainly needing replacement. Problem was not fixed so borrowed an Innova 3030 from friend and getting two P0325 readings back which come back after clearing out and starting engine again. See from forums that this indicates knock sensor and see the knock sensor is buried pretty well. Wondering why getting two P0325 readings every time after clearing out and engine is started when it appears there is one sensor.