Jadczak, of Milton, Del., acknowledged falsifying records at his Philadelphia shop and issuing the stickers.
Investigators say they found the truck had "worn and dangerously thin" brakes after the January pileup. The crash killed 49-year-old David Schreffler, of Fort Washington.
The truck driver, 55-year-old Valerijs Belovs of Philadelphia, has also pleaded guilty to homicide by vehicle. Truck owner Victor Kalinitchii of Philadelphia faces a similar charge.
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