2001 MB E320 Shifted from Park to Drive Without Pressing Brake

Question

My mom was driving a 2001 E320 with a passenger, and had parked on a slight upward incline. She stepped out of the vehicle to speak to someone, and as she returned to get her purse (but before she entered the vehicle), the passenger stepped out of the vehicle. At this point, her and two other saw the vehicle start to roll backwards very slowly (which coincided with the gear selector shown to be in D after it had stopped by bumping a vehicle at a low speed at the end of the driveway).

Three things to note here:

1. The car was parked before my mom left the vehicle (with the engine on), and the car did not move until after she had left.
2. The passenger was sitting in the passenger’s seat, so pressing the brake and changing the gears seems highly unlikely from any angle I look at it.
3. The car was parked on an upward incline, hence the slow roll backwards in Drive, and not an accelerated roll backwards if the car was in Reverse.

Is there anything that could have caused the Mercedes to shift from Park to Drive (seemingly on its own), without pressing the brake? I’m wondering if an intermittent failure of the shift interlock, and/or a failure/slippage of the gear shift mechanism could be at play here. I’d greatly appreciate some insight on this.

Answer 1

I can't think of anything that would cause the transmission to switch from park to drive, or between any gear selection, on its own. I won't say it's impossible, but it would be a very novel event.

It is possible that the gear shift interlock is not working, meaning you can change from park to any other mode without pressing the brake. You can test this by trying it out with the car running, just make sure to do it in a clear spot. If you can change from park to drive without pressing the brake then the most likely scenario is that the passenger accidentally shifted the car when getting out, maybe there was a bag or a strap which got tangled.

If the gear interlock is working then the most likely explanation is that your mother simply forgot to put it in park when she got out of the car. Statistically you are most likely to get in an accident close to your home or destination, many people are thinking about what they are going to do when they get there. From your description there were some distractions around so what is most likely is that it's a simple lapse of attention. I'm not dissing your mother, it could happen to anyone.

If the interlock isn't working and you can change from P to D or R without braking then check the gear lever for debris. It's been known for coins or other thin materials to slide down into the mechanism.