MINNESOTA CITY, Wis. (WKBT) -

Seven school buses were taken off the road near Winona last week after a safety feature was discovered missing.

The Minnesota State Patrol received an anonymous tip and an investigation discovered several buses had a brake sensor removed.

The bus company Minnesota City Bus Service drives around 3,000 kids to Winona-area schools every day.

State Patrol said the tip received mentioned safety concerns and several equipment issues. They believe the missing brake sensor is the most crucial.

"The sensor was a little device that if the brake pressure or hydraulic pressure got low or wasn't there that it would keep that idiot light on on the dashboard, that red light would stay on," said Scott Hannon, superintendent of Winona Area Public Schools.

Eight or nine years ago, a mechanic discovered an issue with a brake sensor underneath a few school buses at Minnesota City Bus Service.

"There was a corrosion problem in the brake module," Hannon said.

After calling the bus manufacturer, the mechanic was instructed to remove the sensor all together.

"Instead of moving the module to a dryer, less corrosive spot, apparently the sensor was removed," Hannon said.

Once the Minnesota State Patrol began investigating, they discovered there was more to the story.

"Clearly this appeared, definitely an intentional act that these parts were tampered with and reinstalled to make it look like they were in original condition," Minnesota State Patrol Lt. Brian Reu said.

State patrol inspects every bus at least once a year, but why did it take nine years to find the problem? They say its not something you could look at during an inspection and know there is an issue, but the recent tip they received pointed them to the problem.

"In this case we followed up partly because of a tip and partly because of issues in the past," Reu said.

"There have been a couple other things that have concerned us over the past few years that we're certainly going to re-look at our contract with Durham services and reevaluate where we're at with them. We have one year left of a three-year contract and we have to look at how has their performance been and are our kids safe when they're driven to and from school," Hannon said.

The Minnesota City Bus Service is owned by a larger company Durham School Services. They released this statement to us saying:

"Durham School Services' top priority is safety; we are currently looking into the results of the recent fleet inspection which placed seven buses out of service due to a missing brake monitor module. Our first priority has been replacing the module to get the buses put back into service; we have successfully reinstated five of the seven buses."

Hannon said there was never an issue with failing brakes during those years without the sensor.

The Minnesota State Patrol said they are close to wrapping up its investigation. Once completed, the investigation will be forwarded to the Winona County attorney for any potential charges.