We have a 2000 trooper, 120K miles, transmission was never serviced. Someone accidentally drained the ATF thinking it was the oil drain. The CHECK TRANS light came on after going a couple hundred miles.

The shop is saying that the draining was not the cause of the transmission's death. Is there a proper way of draining an unserviced transmission to avoid this?

Did they refill it before you drove it and what did they fill it with?
I would get a second opinion and a lawyer.

The 4L30E doesn't fare well to low ATF level, plus never being serviced at that mileage didn't help! The best way to change ATF on a neglected AT is to do it gradually. Draining & filling the main pan on the 4L30E is the best way. You get about 3.5qts out by doing a drain and fill. Fluid level must be checked on a warm idling truck, in neutral on a level surface. ATF should just dribble out of the fill/level check plug. There is two plugs on the AT pan, lower one is the drain, hi up one is the fill / level check.
G/luck
Joel

They refilled the transmission by calling another company in to do the refill. I filed a claim to the shops insurance company and now it's the "customer's burden" to prove that the accidental drain did not kill the transmission.

I took the trooper to aamco today and they drained the ATF, I asked that whatever they do be documented because of insurance purposes. I was told that when the fluid was drained, it was a quart short. ATF smelled burnt. They'll open it up to inspect the transmission and then we'll find out what the cause of death was (hopefully).

Just to update.
The place that drained the tranny paid for the rebuild at the cost of $3K.

Good deal! Atleast you got a new trans out of it after all that. 4L30E's usually die beyond 120K anyway.

G/luck
Joel