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      12-07-2012, 09:08 PM   #18
AndreyT's Avatar

Drives: 2011 335i Sedan, Sport
Join Date: Feb 2011
Location: Northern California

iTrader: (0)

Originally Posted by WhyCry View Post
Did a 360 or two and the engine cut off on me. It's a 335i sport package automatic trans. the engine light was on and but as soon as I turned the car back on it went away. Why would the car stall when it's an automatic?
The traditional cookie cutter automatic transmission does not stall because most of the time the torque converter is unlocked and the engine is not solidly connected to the wheels. The torque converter serves as a "slippable" viscous coupling between the engine and the wheels, preventing stalling even when something blocks the wheels.

Modern high-performance automatic transmissions attempt to operate in locked mode as much as possible, meaning that the engine is solidly connected to the wheels for much bigger percentage of time. When the transmission is locked, a sudden restriction applied at the wheels can potentially stall the engine before the transmission manages to react and unlock itself.