North American car and truck makers have hiked their February and March production plans, but not enough to offset an estimated January shortfall. As a result, first quarter output now stands 9,100 units below where it was a week ago.

What’s more, the overall reduction in the quarter was not equally distributed, as evidenced by a 2.3% increase in Chrysler Group output for the quarter and a 1.5% increase at General Motors Corp.

Current plans call for 4,098,400 car and truck assemblies in North American plants during January-March, still 2.2% above like-2001’s 4,009,200, but 2.8% less than what was previously “booked” for completion.

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However, in an effort to recoup the estimated 39,600-unit underbuild seen for January, production planners last week actually boosted planned output this month by 15,000 vehicles and added 15,500 units to the March output plan.

And while the January underbuild was nearly universal, it was GM and Chrysler that posted the largest increases in February-March output. Indeed, GM followed an estimated January shortfall of 9,100 units with a 13,000-unit boost in February and a 14,000 hike in March. Chrysler more than offset its expected January shortfall of 1,900 units with an 11,600 increase this month and a 5,800-unit gain in March. While some transplant producers also bumped up their February-March plans, for most it was not enough to offset their January “losses.”