Honda's Civic posted a big gain in September, as dealers anticipated the arrival of an all-new 2016 model. Image source: Honda.

Honda (NYSE:HMC) and Toyota (NYSE:TM) both reported strong U.S. sales gains for September that matched analysts' estimates, as both continued to benefit from an ongoing boom in SUV sales in the United States.

Trucks (and clearance sales) powered Honda's solid gain
Honda's U.S. sales rose 13% in September, a big improvement over last month's decline. Sales of what Honda calls "trucks," its crossover SUVs and minivan, drove the gain. Honda and Acura-brand trucks together posted a 26.9% year-over-year sales gain.

Some of that was due to quirks of the calendar. September had one more "selling day" (or put another way, one fewer Sunday) than September 2014, and the Labor Day holiday fell one week later this year than it did last year. Labor Day weekend is a big one for auto sales across the industry.

But there's no question that while Honda has traditionally relied on sedans for much of its bread and butter in the U.S., it's also able to take some advantage of booming demand for SUVs, particularly car-based "crossover" SUVs. 

Sales of Honda's compact CR-V crossover continued to be extremely strong, with a 26% year-over-year gain. The bigger Pilot SUV posted a 31% increase, and sales of Acura's RDX crossover jumped 19%.

The super-popular Honda CR-V outsold the Civic sedan again in September. Image source: Honda.

After a string of difficult months, Honda's Civic sedan was also able to join in the gains. Civic sales were up 27% in September. It's possible that efforts by dealers to clear out inventories had a lot to do with those gains: The all-new 2016 Civic is expected to start arriving at dealers soon.

A similar effect may have been behind a small (2.1%) gain for the bigger Accord, which has struggled with year-over-year declines for much of 2015. The 2016 Accord isn't all new, but it has been given a significant overhaul, with a new grill and many changes to its structure and suspension. The revised 2016 Accords have begun arriving at dealers; it's likely that generous deals were being made to move the last of the 2015s in September.

Toyota did well with crossovers -- and with key sedan models, too
Toyota's U.S. sales were up 16.2% in September. Like Honda, Toyota probably got a boost from the calendar -- but unlike Honda, all three of its key sedan models posted double-digit gains.

Toyota's overall passenger-car sales were up 19%, led by a big jump for the compact Corolla (29.7%) -- as well as surprisingly good gains for the midsize Camry (up 21%) and the hybrid Prius family (up 12.4%). 

An all-new Prius is incoming, and again it's likely that dealers were dealing. But the Camry is more or less unchanged for 2016. Its 21% gain is an impressive one in this hard-fought market segment. Year-over-year sales gains for midsize sedans in general have been hard to come by recently as more traditional sedan buyers have migrated to crossover SUVs.

Sales of Toyota's Highlander jumped in September. Image source: Toyota.

Toyota was able to capture a fair number of those buyers, too. The midsize Highlander crossover posted a gain of almost 18%, for its best monthly result ever, while the smaller RAV4 gained almost 19% -- and the big Toyota Sequoia saw its sales jump over 26%.

Similar results helped give Toyota's luxury Lexus brand a boost. Sales of Lexus SUVs as a group were up over 36% -- good news for Toyota's bottom line, as those vehicles likely carry fat profit margins. Overall, Lexus sales were up 15.8%.

The upshot: SUVs are helping Toyota and Honda hold their ground in the U.S.
The market shift toward SUVs hasn't been as good for Toyota and Honda as it has been for some rivals. Both have historically been dependent on sedan sales in the U.S. But both have adapted since the first SUV boom, last decade, by adding appealing car-based crossovers to their lineups. 

Models like the Highlander and CR-V have helped the two capture some of the buyers who are choosing to leave their Camrys and Civics behind. That should have helped boost North American profits for both as the quarter closed out.