NASHVILLE, Tenn. -- The Channel 4 I-Team has uncovered some serious problems that could affect vehicle emissions inspections in Nashville.

Video: Human Error, Fuses Blamed For Blown Emissions Tests

The investigation turned up some human error but also found the way a car is wired can cause it to fail even if the car’s exhaust is not polluting the environment.

"I was absolutely dumbfounded and outraged,” said driver Connie Watson.

"Just a lot of money wasted there,” said Debbie Henley, who failed the test.

Watson's new Toyota failed its emissions test because, she said she was told, she had a bad gas cap.

“I walked away from the situation with the gut feeling that something is not right here,” she said.

Henley's 2005 GMC Yukon failed because of a burned out fuse in her cigarette lighter, she said.

“I was like, ‘This is only two years old. I haven't had any problems with it,’” she said.

According to the I-Team, drivers all over Davidson County were surprised to learn that they'd failed their emissions test even though their vehicles weren't putting out gases harmful to the environment.

The failures mean repeated trips to testing facilities, and for those who have been to get tested, they know the lines.

“The aggravation of the entire situation was just more exasperating than I could talk about,” Watson said.

City records show that this year, the number of cars failing emissions tests jumped from 1 percent to 8 percent by the time the company Systech was hired in July. Systech brought in new testing software and the failure rate came down, but it is still higher than before at 4 percent.

The figure means that about 20,000 cars in Davidson County are failing the tests, according to I-Team calculations.

Metro Councilman Charlie Tygard said he got a surprise failure because of his gas cap.

"I think it's really strange to go from 1 percent to 8 percent to 4 percent within the space of four months. I think we need to get a handle on that,” said Tygard.

The failures are partly human error.

The I-Team learned from the Department of Health and Systech that when the new testing system started, some inspectors were using the wrong gas cap adaptors that make sure gas fumes aren't escaping.

In fact, some were using broken adaptors, they said.

"There were probably more gas cap pressure failures than what was legitimate,” said Frank Huggins, director of the vehicle inspection program.

There's also the fuse problem.

Systech's new system is so sensitive that in many cars if a cigarette lighter fuse blows, it can't read the emissions output and the car fails.

"It's failing because there's a problem with the system. It's a legitimate failure,” said Systech Vice President Chris Smith

But that failure has nothing to do with emissions. Inspectors said they know how all of this has gone over with drivers.

“As a consumer, I wouldn't be too happy, and it wouldn't make a lot of sense,” Huggins said.

The Health Department said it is not happy about the higher failure rate but said it doesn't feel enough people are failing because of the fuse issue, so it's not going to make a change.

As for the gas cap problem, inspectors have been retrained on using the adaptors. When a car fails now, inspectors will test it again to make sure there wasn't an error.

Make sure your cigarette lighter and radio work before you get your car tested, because if they don't, you may have a blown fuse and fail the test.