Offroad X is right . I just had that happen to me yesterday . One thing though . If you have a stereo system with a capacitor , you have to dissconnected that too or the main power wire will act as a battery from the cap. This will have enough power to run the Xterra's computer for a few days. Dissconnecting the battery works great just make sure the computer was unpowered. Check your short trip odometer to make sure it reset itself. I also had the faults read at Auto zone and the knock sensor went away and the check engine soon light is out too .