And that's a simple example, according to Colonna. He goes on to cite a situation in which a transmission wouldn't budge when the car's headlights were turned on (Cause: a bad ground in the trunk wiring), and one in which a BWM's transmission refused to shift after the owner put on a temporary spare (Cause: The spare had deeper tread than the other three tires, fooling the transmission computer into determining that the car was in a constant turn, and triggering the "curve recognition" function that inhibits shifting while cornering). How is a transmission technician supposed to figure that out?
The problems only get more intense with the increased computing power required by new six-speed transmissions. Many new units, for example, monitor the length of time it takes to shift from one gear to the next, and can spring into action if there's a lag.
"If it starts to become too long, the computer adjusts the pressure in the transmission to try to bring that shift down to where it doesn't take so long," Colonna explains. "They call that ‘shift adapts.' It adapts to the shift, it adapts to the driving conditions, to the driver. If the transmission starts to slip, it'll elevate line pressure to get rid of that slip. As a result, the transmission starts to feel a little bit bumpy on the shift, and in time the transmission may fail."
But, unless your shop has the OEM tool to precisely reset those shift adapts, the transmission can continue to slip or have extremely hard shifts. And even if you have that tool and are able to reset the shift adapts properly, a problem with an engine load device such as the crank sensor or the cam sensor can affect the settings for the shift adapts, potentially bringing that transmission right back into the shop.
"Is this subject large? Yes it is," says Colonna. "I speak for six or seven hours on this subject at seminars. It's really gotten to a whole ‘nother level."
Where does that leave transmission technicians?
According to Tim Schmidbauer, owner of TNS Transmissions in Hales Corners, WI, he and his two technicians rely on their familiarity with traditional transmission technology to guide them, but when that isn't enough they turn to Colonna's group and to the Automatic Transmission Rebuilders Association (ATRA). "They have a hotline you can call and have a technician work with you on electrical issues or hydraulic issues, or whatever it might be," he says.
"Sometimes you want to tear your hair out," Schmidbauer says of diagnosing complicated transmission problems. "Still, in the end we always figure it out."
On a final note, Schmidbauer, whose shop does transmission work for the City of Milwaukee, WI, fleet, often has to deal with a decidedly low-tech problem: unskilled fleet drivers.
"It's not their vehicle, so they may have a problem, and instead of addressing it right away they let it completely fail," he says. "With automatic transmissions, you could get slips or flutters between shifts, fluid leaking; if you don't catch it you could burn the transmission up.
"It would be nice if they could catch the problem before it becomes a complete overhaul," he says, recommending that drivers in doubt just pull over and call the tow truck.