Factual error: When Gabriel turns off the lights in the tunnel, we see a shot of cars heading towards the police car as the lights turn off, and not one of them turns its headlights on. In reality, with that many cars in the tunnel, there'd be at least one that was fitted with auto-lights.
Factual error: In the beginning of the movie after the scene where John watches his daughter go inside, he is called on his police radio. The gentleman on the other end is in fact talking to him on a land-line telephone and not a radio, but from Johns end you hear the mic being keyed on and off. Police radios cannot make or place telephone calls and vice-versa. (00:06:45 - 00:07:50)
Suggested correction: Although very unpopular and very unlikely to have been installed in a Police car, some radios can indeed ring landline telephones. They were known as "Mobile Radio Telephones" but they tended to be extremely unreliable.
Other mistake: When Gabriel looks at McClane's police record it mentions McClane receiving a commendation for the Chicago airport incident in 1990. That incident happened at Dulles Airport in Washington D.C., not Chicago.
Plot hole: When Lucy is stuck in the elevator, and they re-activate the elevator and turn all the lights on, Lucy should have been able to push the buttons and get to the floor. She did not have to wait for someone to rescue her.
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: This is supposed to be an F-35B, the STOVL version with the additional lift jet. The B model has no internal guns, let alone two firing from the bottom of the air intakes. The only gun it can carry is fitted in a multi-mission pack attached to the belly. (01:54:25)
Deliberate mistake: While McClane drives in the tunnel, Gabriel orders, "Open the gates on the north side entrance." A few shots later the signal light changes from red to green and the north gate opens. The "warning" sign is backwards in this flipped shot. Then, when Gabriel opens the gates at the south entrance, there's a proper shot of the "south" gate opening. The two shots of the "north" and "south" gates opening are the same, but one is reversed. All the dirty smudges on the signs, booths, etc, are identical. (00:41:20 - 00:42:05)
Continuity mistake: While McClane and Farrell are in FBI Police car 279, the windshield's rearview mirror repeatedly vanishes and reappears. (00:38:25)
Continuity mistake: During the traffic jam early in the movie, John and Matt get out of their car and walk away on foot. In the next aerial shot looking down, you see someone stepping out of the very same car they were in. (00:25:27)
Continuity mistake: When driving the semi, McClane collides with the rear of a black BMW, but when the camera shifts to a different angle the collision continues with a cut of the truck hitting a Mercedes from earlier in the scene. (01:48:50 - 01:51:45)
Continuity mistake: When inside the stationary semi-truck the actors are swaying and moving as though the truck is travelling, but it has not yet left the warehouse. (00:50:00)
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.
