Continuity mistake: While McClane is taking control of the Freight liner during the final chase, he jumps onto the driver's steps, and we see the driver's side window is closed, he shoots the driver and whips the door open, and the window is now open. He climbs into the truck and slams the door, and the window is once again closed. There was obviously no time for the window to be opened and closed during the fight.
Continuity mistake: At the very end when McClane is talking to Farrell, he has three steri-strips over his left eye, but when he goes back to his daughter he only has two.
Factual error: The cyber attack takes place on the 4th of July which is a national holiday, the stock market is closed and so are government offices, no politicians are meeting at the Capitol.
Factual error: There are several mistakes after McClane steals the 18 wheeler that give away the highway scenes were shot in California instead of Maryland. There are palm trees visible at one point outside the window. There are highway signs that indicate Route 118 and Highway 110, both in California. The scene with the fighter jet is supposed to be on I-695, the Baltimore Beltway, but that road is single-level, not multi-level as the movie shows. A green bridge is visible after part of the highway collapses but there is no bridge that looks anything like that on I-695.
Factual error: Near the end of the film there is a shot of the FBI helicopters turning. Mountains are visible in the background. This film is supposed to take place on the east coast. There are no mountains that tall on the east coast.
Continuity mistake: At the end when McClane shoots through himself to kill the bad guy, it's though his right shoulder into the bad guy's right shoulder. The next shot of the dead bad guy has the wound in his left shoulder.
Plot hole: After McClane, agent Johnson, and Ferrell leave in the police car, Agent Johnson radios another agent to have DC police clear a path for them. Then on Gabriel's screen it says they have a voice match to Farrell. The problem is Farrell never said a word, so how would they have a voice match to him? Without the voice match they never should have found them.
Suggested correction: The agent says "Ferrell" over the radio which in turn gets picked up as a name match on Gabriel's screen as they were scanning for anyone using that key word. Not Ferrell's actual voice but anyone mentioning his name over the radio.
If it was just looking for anyone saying the word Farrell it would have been a "voice" match. A voice match implies but they got a match to Farrell's voice.
In this context it is a match on the name "Farrell" that was spoken, hence it is a "voice match." It's clunky but still works grammatically.
Factual error: When McClane and Ferrell are stuck in the intersection with the helicopter shooting them, the bad guys pull up the scene from a camera on the building. Clearly the camera is stationary, so why is the shot on the computer moving?
Factual error: When the hackers start hacking the traffic cameras there are several shots of vehicles crashing on the computer screen. These shots are supposedly coming from traffic cameras but some contain complex movements such as a crane shot that was obviously done by a real camera.
Continuity mistake: John M is driving to the Eastern electricity station and chatting. The view out of his window shows him driving past the same distant hill at least three times. Also the speed is faster out of the passenger's side than the driver's.
Factual error: After the eastern hub explodes from the gas, and after Mathew's rant, McClane looks out over the city as the power goes out and all the lights begin to shut off. But all the headlights of the cars on the streets also begin to turn off, despite not being connected to the grid.
Audio problem: Why does the whole city make a 'whooom' noise when the power turns off? And each block makes exactly the same sound.
Factual error: They crash their BMW, and Doloris comes on in the On-Star system. On-Star has never been available in BMW vehicles, as it is a wholly-owned subsidiary of General Motors. BMW does offer a similar service called BMW Assist, but this was not available in any BMW model at the time of this movie.
Suggested correction: Where did you get OnStar from? It was "RoadAssist", OnStar is not mentioned at any point. Nor do they crash the BMW, Matt whacks it with a bin.
Factual error: When John McClane is driving the semi, an F-35B Lightning II is called in to destroy the semi - the only problem is no variants of the F-35 were in operational service in 2007, and are not expected to be until December of 2015.
Factual error: 0.7% of the electricity generated in West Virginia (as of 2011) is from natural gas. The plant in the movie would have been a peaking unit, only operated during the day. Shutting down a power plant that is not operating would not cause a black out. Further evidence that the unit is not operating is that only three security guards seem to be on the premises. You can not operate a power plant with three security guards.
Factual error: In the scene where McClane jumps off the fighter jet he slides down at 100+ feet of highway concrete but when he reached the bottom his jeans are not torn in any new places. Any fabric rubbed against concrete for any significant distance would be shredded or (if conditions were perfect) at least frayed.
Factual error: Throughout the movie, they depict the evil computer genius being able to manipulate (virtually any) distant objects, like video webcams and doorknobs, from his keyboard - just through sheer computer-genius awesomeness. When, to actually do these things, everything would have to be pre-rigged with servo motors and controllers, and be somehow connected on the web.
Continuity mistake: McClane's shoulder holster disappears while fighting in the hanging truck in the elevator shaft. We can see he has the holster again (albeit a different kind) before the fight with the parkour guy.
Factual error: The Woodlawn shot of the hackers killing the security guards show mountains. There are no mountains in Woodlawn.
Continuity mistake: In the beginning once McClane and Matthew have escaped the apartment, and are going through the alleyway, when John gets in the car and throws it in reverse look to the left of the screen. The back driver's side window is rolled down about 2-3 inches. The remaining camera shots during the escape show the window being rolled all the way up.
