DETROIT – Auto makers pulled in the reins on January production after two consecutive months of overbuilding their schedules, according to estimated output for the month by Ward’s.

North American production for January will finish at an estimated 1.334 million units, nearly 45,000 units (3.2%) below the industry’s cumulative schedule for the month (see related data). . This includes mid-month schedule adjustments at Ford Motor Co. Most of the shortfall will be in cars (30,300 units), with some downturn in trucks (14,500).

The majority of the shortfall appears to have more to do with tweaking the inventory of certain vehicles, rather than a reaction to expectations of an overall inventory problem due to slowing demand.

There’s a lot of downtime this month at General Motors Corp. plants building Buick, Pontiac and Saturn midsize cars, and large cars built at its Orion, MI, facility. At the same time, GM is running steady overtime for plants building Chevrolet Impalas, Monte Carlos, Malibus and Pontiac Grand Ams.

Production of the redesigned Toyota Corolla appears to be ramping up slowly at Toyota Motor Mfg. North America Inc. in Canada and at New United Motor Mfg. Inc., causing some of the car shortfall.

The smaller gap on the truck side is a result of underbuilds at each of the Big Three, despite rampant overtime at GM and Ford plants building large SUVs and pickups. But GM slated considerable downtime at its van plants, and DaimlerChrysler Corp. appears to have cut back overtime at its truck facilities. The non-Big Three manufacturers, on the whole, are set for an overbuild, but not enough to offset the decline at the Big Three.

Meantime, estimated Jan. 31 inventory of domestically built light vehicles has been revised to 2.636 million units, an 8.1% increase from the prior month, but 20.9% below year-ago.

Days’ supply for domestically made light vehicles will jump to 77 on Jan. 31 – a normal level for this time of year – from the prior month’s artificially low 59, and below like-2001’s 83 days’ supply.

Including imports, Ward’s estimates total light-vehicle inventory at 3.125 million, 18.8% below year-ago and equal to a 74 days’ supply, compared with like-2001’s 80 days.