That has triggered a modest, though noticeable, trend upward in givebacks over the last few weeks, according to trackers. It's a sharp turnaround for an industry that had been trying to wean itself off the givebacks that cost manufacturers billions of dollars in lost profits.
Last year's surge in demand—U.S. new vehicle sales rose more than 1 million units to 15.6 million for 2013—had permitted makers to trim incentives and demand more for their products, with average transaction prices reaching record levels during the latter half of the year.
(Read more: GM, Ford dealers boost discounts on big trucks)
But the average price paid after working in both incentives and options dipped sharply in January to $29,882, down 3 percent from December. And while incentives were actually down in January, some analysts said makers might have gotten too stingy, contributing to lower sales already hurt by cold weather.
While it's still too early to tell what February will bring, ALG is forecasting a "short-term spike," with incentives likely to climb as much as 15 percent to 20 percent longer term. And that's assuming that makers don't decide to ramp up givebacks even more in a bid to boost market share as well as sales.
(Read more: What the market is missing with General Motors)
There is, warns editor Karl Brauer of Kelley Blue Book, "the very real possibility of an incentives war if sales don't pick up in the coming weeks."
Which is why investors reacted in panic when it was initially reported that GM was going to offer that $7,000 discount across its vast truck lineup. The maker took a 3.4 percent hit to its stock price before it made it clear that the givebacks were limited to only about 10 percent of its Chevrolet Silverado and GMC Sierra full-size pickups.
The real test will come in February and March as automakers wait to see if sales recover.
—By CNBC Contributor Paul A. Eisenstein. Follow him on Twitter
@DetroitBureau or at thedetroitbureau.com.