Check out the latest GM earnings call transcript.

General Motors (NYSE:GM) said that its U.S. sales fell 2.7% in December, as sales of its new pickups weren't strong enough to overcome big year-over-year declines in sales of its sedans.

For the full year, GM's U.S. sales were down 1.6% from 2017.

A 2019 GMC Sierra, an upscale full-size pickup truck

Sales of GM's full-size pickups were flat in 2018, but it appears to be getting strong pricing for the all-new 2019 GMC Sierra and its Chevrolet sibling. Image source: General Motors.

How GM's 2018 U.S. sales compare to rivals'

Most of GM's rivals also lost ground year over year in 2018. The big exception was Fiat Chrysler Automobiles (NYSE:FCAU), which rode its pickup-and-SUV-heavy lineup to a solid sales gain.

Automaker 2018 U.S. Sales Change vs. 2017
GM 2,954,037 (1.6%)
Ford Motor Company (NYSE:F) 2,485,222 (3.5%)
Toyota 2,426,672 (0.3%)
Fiat Chrysler Automobiles 2,246,467 8.4%
Honda 1,604,828 (2.2%)
Nissan 1,493,877 (6.3%)

Data sources: Individual automakers, Automotive News.

What worked for GM in 2018

Crossover SUVs

GM put a lot of money and effort behind revamping its entire line of crossover SUVs in 2016 and 2017. As expected, it reaped the benefits in 2018, with five models setting new sales records:

Vehicle 2018 U.S. Sales Change vs. 2017
Buick Encore 93,073 5.7%
Chevrolet Equinox 332,618 14.5%
Chevrolet Trax 89,916 13.4%
Chevrolet Traverse 146,534 18.6%
GMC Terrain 114,314 33.8%

Data source: General Motors.

As a group, sales of GM's crossovers rose 7% in 2018 to just over 1 million.

A dark red 2018 Chevrolet Traverse, a seven-passenger crossover SUV

Sales of the all-new 2018 Chevrolet Traverse crossover SUV were up almost 19% in 2018. Image source: General Motors.

Midsize pickups

While sales of GM's full-size pickups were roughly flat in 2018 (more on that below), its one-size-down Chevrolet Colorado and GMC Sierra each had a good year; sales were up 19% and 4.3%, respectively.

The Chevrolet Bolt EV

You may have heard that U.S. sales of the little electric Chevy fell almost 23% in 2018, but that's only part of the story. GM only produces the Bolt in one factory, in Orion Township, Michigan, and exports it to several markets around the world.

What happened was that demand in Canada and South Korea exceeded GM's expectations, so it sent more Bolts out of the U.S. -- leaving its U.S. dealers with tight supplies for part of 2018. We won't have final full-year totals for another day or two, but it's already clear that higher Bolt sales in Canada and (especially) South Korea offset most or all of the decline in U.S. sales of the electric Chevy.

GM is already addressing the supply issue: It increased production of the Bolt in the fourth quarter of 2018. The company said today that it expects sales of the Bolt in the vehicle's major markets (the U.S, Canada, and South Korea) to rise in 2019.

What didn't work for GM last year

Full-size pickups

The jury is still out on GM's all-new full-size pickups, the Chevrolet Silverado and GMC Sierra, but we know this: 2018's sales were flat versus 2017's.

To be fair, GM was selling a mix of old and new models for much of 2018, which complicates the task of gauging the new trucks' success. And to its credit, it has been stingy with incentives on the new trucks.

But by the simplest of measures, GM's pickups had a tough year: Sales of FCA's Ram pickups rose 7% in 2018, while Ford's market-leading F-Series gained 1.4%.

A 2019 Cadillac CT6, a large luxury-sports sedan, parked on a city street

Critics love the Cadillac CT6, a big luxury sedan with surprisingly nimble handling. But sales have slumped, and GM says it's on the way out. Image source: General Motors.

Sedans

More and more buyers are choosing crossover SUVs over sedans. That's good news for GM's crossovers -- but it's not so good for the company's sedans. Most of GM's sedan models were overhauled in the last few years, and most of them are very competitive with the best global rivals -- but most saw sales plummet in 2018.

GM has responded by announcing the closure of several North American factories that make sedans: A number of formerly big-selling models, including the Chevrolet Cruze and Impala, and a few critical favorites like the superb Cadillac CT6, will be going away after 2019 -- as GM, like many rivals, focuses on higher-profit SUV and truck models.

The upshot: GM is choosing profit over sales right now

GM is willing to give up on slumping sedan models because it wants to maximize its profit margins -- not only on general principles, but because it's investing heavily in a new generation of battery-electric vehicles that will begin rolling out in a few years.

On balance, GM appeared to have a solidly profitable 2018 in North America, thanks to those crossovers -- but it's clear that the company, like most of its rivals, has further work to do over the next couple of years.