Some mean people are already referring to this teen tearjerker based on Gayle Forman’s 2009 young adult novel “The Fault in Our Cars,” since the tragedy involves not a cancer diagnosis but an automobile accident that leaves one of the leads in a coma. But “If I Stay” doesn’t come close to achieving even the modest level of genuineness that Josh Boone managed in “The Fault in Our Stars.” To the contrary, it has all the authenticity of a project written for the CW network by Nicholas Sparks.

It also spotlights a disappointingly poor performance by Chloe Grace Moretz, who plays Mia Hall, a Portland high school student who’s also a prodigy on the cello, spinning out classical melodies although her parents Denny (Joshua Leonard) and Kat (Mireille Enos) were in their younger days part of the local rock scene, and they and Mia’s younger brother Teddy (Jakob Davies) still prefer that sort of popular music. Nonetheless her family supports her passion, and her playing also attracts the attention of handsome classmate Adam Wilde (Jamie Blackley), the lead singer in a rock band that’s already achieved local celebrity and is on the verge of getting a record deal.

As adapted by Shauna Cross, the movie—directly prosaically by R.J. Cutler—early on shows Mia and Adam suffering a speed bump in their relationship as she awaits a letter that might invite her to attend Juilliard in New York, a possibility that distresses Wilde, who suffers from a history of abandonment. It’s during this tense period that the Halls go off for a drive through the snowbound Oregon forests and get into a terrible crash on the icy road. Mia awakens as a disembodied spirit observing her comatose body being loaded into an ambulance. (She jumps in and accompanies herself to the hospital.) The fates of her father, mother and brother are left hanging, to be revealed gradually as the narrative progresses for maximum emotional punch.

That narrative consists of the spectral Mia haunting the hospital corridors, observing events in a kind of limbo as Adam, her best friend Kat (Liana Liberato) and her grandpa (Stacy Keach) worriedly await word on her condition and a nurse in the intensive care unit (Aisha Hinds) encourages her bedridden form to fight to return to consciousness. Mia debates whether to move toward the light that occasionally beckons her as the scope of the tragedy sinks in.

Meanwhile an avalanche of flashbacks tell us about the young Mia’s (Gabrielle Cerys Haslett) falling in love with the cello, her father’s decision to give up his musical aspirations and become a teacher to support her dream, and—most importantly—her romance with Adam, which includes trips to cello recitals, rehearsals and gigs of his band, jamborees at the Hall house, Romeo-and-Juliet like trysts as Adam climbs a trestle up to her second-storey room, and Halloween costume parties, as well as the growing strain between them as Mia’s Juilliard prospects become more palpable and Adam’s career takes off. The juxtaposition between present and past continues until Mia abruptly makes her decision about whether to stay among the living or go into the light—though hardly anybody will have the slightest doubt about what that decision will be.

It’s obvious that Cutler (a documentary filmmaker making his first fiction film) and Moretz (who’s straining to move into more mature roles) want to get viewers’ tears flowing in the worst possible way, but despite their strenuous efforts most people’s eyes are likely to remain resolutely dry. That’s because they never manage to make Mia anything more than a bland high school kid. Even the scenes when she’s entranced in her playing come across as more contrived than truthful, and the ones she shares with Blackley, a handsome fellow inhabiting an equally shallow character, are no better. (He was far better in the little-seen British thriller “U Want Me 2 Kill Him?”) It certainly doesn’t help that the songs performed by Adam’s band Willamette Stone sound so banal, barely a step removed from bubblegum pop tunes. It’s hard to believe that the group is soaring into the stratosphere on the basis of such fluff.

But the triteness of the songs is matched by Cross’ dialogue. Barely a line spoken in the course of the picture has an authentic feel; everything sounds like it was written for a teen soap opera. That has an unfortunate effect on the performances of Moretz and Blackley, but it’s even more debilitating to those of Enos and Leonard, who are given pseudo-hip, genial stuff to say that resembles lines lifted from a bad network comedy-drama, and the turn by Liberato, who comes off like the composite of every smart-alecky best friend you’ve ever seen on a Disney Channel sitcom. Grizzled Keach goes for the emotional jugular, especially in his bedside scenes with the comatose Mia, but he’s pro enough to pull the lachrymose material off; Hinds is less fortunate as the supportive nurse. Davies at least avoids making little bro Teddy obnoxious. On the technical side the movie has a nice sleek look, with cinematographer Arri Alexa taking advantage of the attractive Vancouver-for-Portland locations and Brent Thomas offering a lived-in production design. But what’s with the time-uncertain set decoration by Louise Roper, which, for example, has Mia playing a Bach Brandenburg Concerto via a vinyl disc on a little red phonograph that looks like a refugee from the 1950s? When is the movie supposed to be set, anyway?

Not that such questions will bother anyone swept up in the supposedly destined romance of poor Mia and not-so-wild Wilde and the tragedy they’re called on to endure together. It’s extremely doubtful, however, that their plight will elicit the same degree of sobbing that Hazel Grace and Augustus’ did. At one point, Mia’s mother consoles her daughter by remarking that eventually you realize that life is “one big, fat, gigantic, stinking mess.” “If I Stay” reminds you that the description can apply to some movies, too.