Can anyone explain exactly how turning off ESP allows my car to escape from a snow drift that it could not escape with the ESP turned on?

 

Because with esp off. the ASR and ESP are not active for accelerating. Braking force is applied to one spinning drive wheel so it helps to transfer traction to the wheel with the most grip. Basically drive control torque is switched off.

 

Sorry,I'm not following you Russell. Let me try this again. While stuck in a snowbank with ESP on, wheels spin and the car doesn't move either forward or back. Turn ESP off and the car drives out of the snowbank almost lick it's on a dry road. This seem counterintuitive. I thought ESP was supposed to apply brakes to the spinning wheels so more power was delivered to the other wheels. But, in fact, wheels were spinning with ESP on.

 

ESP off switch does not completely deactivate your system, but rather puts in another mode, When stationary and trying to pull away in snow the wheel slip is very high so the ASR function of the ESP starts to limit the torque by closing the throttle and braking both rear wheels. So you go no where. Now you switch ESP off. Torque is not limited by the throttle anymore because ASR is now off and the ESP unit will brake only ONE spinning wheel at a time not both. Once you reach 40 to 60km/h the ASR will function again. Limiting torque via the throttle.