Lee also is Chrysler's head of engine, powertrain and electrified propulsion systems engineering and is on Chrysler's 20-member Group Executive Council.
Gradu's departure was sudden. He was conducting media interviews as late as Tuesday at the Detroit auto show media preview.
Gradu, a native of Bucharest, Romania, has held increasing responsibilities with Chrysler since joining the company in 2007 from the Timken Co., a bearings and steel supplier to the automotive industry.
Chrysler delayed the launch of the Cherokee nearly two months until late in October to properly calibrate the software that operates its 9-speed automatic transmission and its disconnecting rear driveshaft and differential.
Gradu's teams were responsible for the way the system worked.
Chrysler plans to use an all-wheel-drive system similar to that used in versions of the Cherokee in other future vehicles, including versions of the upcoming 2015 Chrysler 200.
The delay was costly for Chrysler, CEO Sergio Marchionne said in a third-quarter conference call with analysts. Chrysler initially tested every Cherokee that came off the line to make sure that its drivetrain was operating as intended. It has since stopped test-driving each vehicle.
A Chrysler spokesman declined to comment.