Audio problem: Just as McClane and Farrell are about to leave the Eastern Power Hub, Farrell goes on a long rant and his mouth does not match the words he is saying. [In the unrated version of the film, the rant concurs with Will's mouth movements, but the mistake is valid for the regular version.]Joel Amos Gordon
Continuity mistake: When John and Mai are fighting at the power plant, John tosses Mai up against a glass board. Her pony tail has come undone and her hair is a big mess. You see Mai from the back as she gets up to come after John. Her hair is now neatly combed and back in a pony tail. But as she begins to fight, her hair is once again undone and messy.
Factual error: During the chase with the semi, McClane is shown struggling to keep the truck under control with the freeway collapsing/blowing up all around him. He is shown making a left turn on a ramp, and the truck going up on 9 wheels, almost rolling. The shot cuts back to McClane steering left to to try to control the truck. If he were to steer left, as depicted, he would be guaranteed to roll the truck. If he was trying to get the wheels back down, he'd have to steer into the roll, or right, to bring it back on the wheels. At the end of the shot, you can actually see the stuntman brings the wheels down with a short right turn of the steering wheel. The similar entry in corrections is right, the person making the correction is wrong. During 15 years of driving a semi, I had a very similar situation with the truck almost rolling. I had to steer into the roll to bring the truck back on the wheels, not away from it, as the film showed McClane doing.