2002 ML320 does it have vac door locks?
 

Daughter says backseat doors not locking/unlocking properly. Does this have vac locks like my 300SD and actuators in each door? Could this be the problem?

Vacuum, no. Actuator in each door, yes

So you are saying the problem is probably an electrical problem?

What exactly are the symptoms??? ML door locks are notorious for "ratcheting", or going up and down real fast. If that's the case the actuator is bad. Expect to pay ~$200+ at the dealer.

Ouch. She just left for Auburn so I have a reprieve. I did notice that the rear passenger door was very hard to get the lock to release by pulling on the outside handle. Think she says it locks OK with the remote but will not unlock. Not sure. But will worry about that tomorrow.