it likely does, but significantly less so than the synoptic gospels, based on my understanding that the gospels of Matthew and Luke are thought to have used the same sources; The Gospel of Mark, and the "Q" source. [See below for Q source] . The Gospel of John is the least consistent gospel to the others, because John apparently did not have access to the Q source. This is the reason that for the most part Mark's, Matthew's, and Luke's gospels tell most of the same stories with most of the same details, while John's gospel contains some contradictions and omissions to the others. One example of inconsistence, John's Jesus asserts himself as the messiah, claiming "I am the bread of life." (John 6:35) He talks about himself much more often in the first person, drawing more attention to his role in the events. In Mark, Jesus hardly ever talks about himself, instead talking about the future and the coming kingdom. He speaks with knowledge of the divine, but does not "claim responsibility" for it per se. In a way, the Jesus of the synoptic Gospels tends to be the more "humble" Jesus, compared to the almost "look at me! I'm the Messiah!" tone that John presents (just joking. That is not a direct quote from any gospel).

So at any rate, historians tend to take the synoptic gospels more seriously in part because of their relative proximity in time to the life of Jesus, and in part because of their apparent access to a lost source from even closer to the life of Jesus. Since John seemed not to have access to this source, and since his presentation seems more motivated by evangelism than history (evident in his "look at me" depiction of Jesus. He is almost a cult-of-personality in John's Gospel, where he was more modest and humble in the synoptics), historians are slower to accept the validity of John as a source on the actual history of Jesus. I don't think its safe to say it is entirely fiction, because John presumably had the synoptic gospels themselves for his sources. He does make marked departures from the synoptic gospels, so those departures are more likely evangelist fiction. This is not to say that the synoptics are totally historically accurate. They are probably just as evangelically motivated as John, but again, they are more valuable historical texts because of their consistency.

edit: I'd have to do a lot more research to come up with more examples of contradictions, which is what I think you are looking for. This was off the top of my head from past research, which included Jesus, A Revolutionary Biography, and The Historical Jesus, by John Dominic Crossan, as well as The Jesus Dynasty by James Tabor. All are engaging and fairly easy college-level reads. I'm certain you could google something like "contradictions between gospels" and find lots of material pointing towards examples from both academic and religious standpoint.

edit 2: Sorry, let me correct myself. I said before editing that Mark Matthew and Luke relied on a single lost source, but in fact the Q source influenced only Matthew and Luke. Matthew and Luke contain material taken from Mark and from the Q source. I clarify further below. Sorry for the runaround with all the edits. I should have reviewed better before posting!