Blue Bird is recalling more than 4,000 Type D All American school buses to fix a potential electrical short problem affecting the engine cooling fan.

The manufacturer notified NHTSA last week of two separate but similar recall campaigns for buses equipped with Cummins ISB-02, ISB-07 and ISB-10 engines. One of the recalls affects 3,992 vehicles manufactured from May 29, 2006 through Aug. 7 of this year, while the other affects 466 buses manufactured from July 16, 2006 through Aug. 3 of this year.

Blue Bird said an incorrect combination of a flat washer and serrated nut was installed on the bolt that secures the starter cable retaining clamp to its attaching bracket that is located at the front of the engine above the engine cooling fan. The company added that the flat washer prevents the serrated nut from locking against the attaching bracket.

Over time, the serrated nut may "back off" and allow the starter cable to fall and contact the fan hub. If this occurs during vehicle operation, the cable covering may "abrade" and result in a short and fire.

Blue Bird added that it would begin notifying owners and dealers of the free repair by late September.