Johnson already had been suspended for the first eight games of the 2007 season for violating probation on a gun charge. He spent two months in jail and was released in May.
"We are upset and embarrassed by Tank's actions last week," general manager Jerry Angelo said in a team release Monday. "He compromised the credibility of our organization. We made it clear to him that he had no room for error. Our goal was to help someone through a difficult period in his life, but the effort needs to come from both sides. It didn't, and we have decided to move on."
Police in the Phoenix suburb of Gilbert said Johnson was stopped for driving 40 mph in a 25 mph zone at 3:30 a.m. Friday and the officer made observations that led him to believe Johnson was impaired.
Sgt. Andrew Duncan, a police spokesman, said Johnson was arrested for "DUI Impaired to the Slightest Degree" but was released without being booked or charged.
Duncan said Johnson was taken to the Gilbert police station, where officials drew blood for a blood-alcohol content test before his release. He described Johnson as "very cooperative."
Test results weren't expected for up to two weeks, and they would be sent to Gilbert town prosecutors for consideration of any charges.
Johnson had called his suspension an "opportunity for me to move forward." NFL commissioner Roger Goodell had said the suspension could be reduced to six games if Johnson had no further involvement with law enforcement and underwent counseling.
Last December, police raided the 300-pound defensive tackle's suburban Chicago home and found six unregistered firearms — a violation of his probation on an earlier gun charge.
That charge stemmed from Johnson's 2005 arrest after a Chicago nightclub valet reported seeing Johnson with a handgun in his SUV. He subsequently pleaded guilty to a misdemeanor charge.
Two days after last December's raid, Willie B. Posey, Johnson's bodyguard, was shot and killed in an early morning fight while he and Johnson were at a Chicago nightclub.
Johnson was suspended by the Bears for one game for being at the club. He played in the Super Bowl as the Bears lost to Indianapolis.
In March, Johnson began his two-month jail stint. Last month, he pleaded guilty to a misdemeanor weapons charge stemming from the December raid as part of a deal with prosecutors that kept him from serving more time in jail. He was ordered to serve 45 days, which he served concurrently with the sentence for violating his probation.