This has been an awful year for automaker stocks. Since the calendar flipped to January, the S&P 500 Automobiles Index, which includes major publicly traded car makers, has shed about 15% of its market value.

Compare that against what's now a 3.8% total return for the S&P 500 this year, and car stocks have handed investors some pretty awful underperformance during a year when relative performance has mattered a lot.

But at least one car stock looks ready to try and pull off an about-face in the final stretch of 2018: I'm talking about General Motors (GM) - Get Report .

GM made headlines earlier this month when the firm called for the Federal government to mandate a higher sales mix of electric vehicles in the years ahead. And it caught even more attention Wednesday, when the firm reported better-than-expected third quarter earnings numbers.

Analysts were expecting $1.25 in profit for the quarter, on average, but GM posted a $1.87 profit on a comparable basis, sending shares up 9% on the session.

Now, that earnings-fueled breakout is driving a potential long-term reversal on the chart:

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You don't need to be a trading expert to figure out what GM's trajectory has been in recent months. Since peaking in early June, shares have been selling off in a well-defined downtrend, unwinding on every successive test of trendline resistance.

Earnings changed that, sending shares above their trend channel for the first time in five months.

Now, with the downtrending channel in the rearview mirror and positive sentiment baked into shares right now, GM looks primed for more upside. Short term, expect some sideways consolidation as shareholders absorb the scale of Wednesday's gap higher. Longer term, with no nearby resistance to the upside, shares have room to trend higher.

Relative strength provided a bit of an early warning that GM was moving toward a leadership position. GM's relative strength line actually broke above its own downtrend more than a week ago, signaling that GM's run of systematically underperforming the S&P 500 was ending.

For investors looking for a buying opportunity in the beaten-down automaker industry, now looks like as good a time as any to buy GM.

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This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.