To say that Fiat Chrysler Automobiles' (NYSE: FCAU) Jeep brand has been crushing sales figures each month over the last couple of years would be an understatement. The Jeep brand, along with the Ram Truck brand, are practically keeping the lights on at FCA with their surging sales. According to industry analysts' estimates, FCA's SUVs and pickup trucks account for more than half of FCA's pre-tax profits.

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Chart by author. Information source: Fiat Chrysler Automobiles monthly sales releases.

In May 2015 the Jeep brand posted its best monthly sales figure ever and its 20th consecutive month of year-over-year gains -- and impressive gains as you can see in the graph above. Further, Jeep's Cherokee and Wrangler each recorded their best sales months ever.

Jeep is killing it. Period.

As long as sales of Jeep and Ram Truck brands stay strong, investors are hopeful that FCA can perform a companywide turnaround, rewarding investors with a quickly rising stock price. However, the recent announcement that the Jeep Grand Cherokee's 2017 redesign will be delayed by a year, or even two, could hinder sales of a key FCA product.

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Jeep's 2014 Grand Cherokee. Image source: Fiat Chrysler Automobiles

How important is the Grand Cherokee?
While the full-size Ram Truck is likely FCA's most important product, the Grand Cherokee isn't far behind. Looking at sales from January through May last year, the Grand Cherokee outsold any other Jeep model in the U.S. and was only outsold by the Ram Truck in all of FCA's vehicles in the U.S. market.

However, the Grand Cherokee's year-over-year sales have slowed: From January through May 2015, sales have only increased 4% compared to last year. Meanwhile, the Cherokee, Wrangler, and Patriot, posted respective year-over-year gains over the same time period of 30%, 20%, and 35% and now the Cherokee and Wrangler outsell the Grand Cherokee.

So, as sales slow for the Grand Cherokee, why in the world is FCA delaying the redesign of a product that hasn't been new since the 2011 model year?

What's the deal?
FCA CEO Sergio Marchionne noted that the model is being delayed so that engineers could take a complete relook at the vehicle's underpinnings, which will share architecture with the larger and more expensive Grand Wagoneer. The Grand Wagoneer's launch is targeted for the fall of 2018 and is aimed to compete with luxury SUVs such as the Range Rover, and would be a very profitable move for the automaker. Unfortunately, the Grand Wagoneer's launch could also slide even further down the road, as well.

The reason this matters for investors is because a one or two year delay on the Grand Cherokee's redesign -- in addition to a delayed launch of the highly anticipated Grand Wagoneer -- could make FCA's goal of reaching 1.9 million worldwide Jeep sales by 2018 difficult. Furthermore, it could hinder FCA's plan to raise its profit margin in its North American region beyond its 4% level. Missing those targets would disappoint investors and Wall Street analysts alike.

What's FCA thinking?
Consider that Marchionne continues to say the auto industry needs consolidation as too many automakers are investing massive capital in similar engines, platforms, and vehicles. For that reason Marchionne has been a proponent of industry consolidation and has been rumored to be looking for a merger partner. One possible reason for these delays is that it would enable the automaker to delay some research and development costs for these vehicles while trying to attract a merger partner.

Ultimately, through 1990 Jeep was the No. 1 SUV brand across planet earth; as of last year, though, Jeep was only the No. 6 brand in the world and had dropped to only No.3 in NAFTA. If FCA plans to achieve its goal of returning Jeep to its No. 1 global spot, it needs the Grand Cherokee's redesign and the Grand Wagoneer's launch, sooner rather than later.

If the Grand Cherokee's redesign is delayed until 2019, investors should ask themselves why a company isn't focusing on one of its most important and profitable models at a time when SUV sales are booming in the U.S. market.

Daniel Miller has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.