PeachParts Mercedes-Benz Forum - View Single Post - Turning off an engine / run away vehicles

retmil46 · #9 08-28-2012, 12:21 PM

Not to mention the old adage "you have more horsepower in your brakes than your engine".

IMO, as it's already been stated in this thread, boils down to operator error - not knowing what to do in an emergency situation ahead of time, coupled with the panic of being caught in said situation.

Lack of drivers ed, owners never bothering to crack the owners manual, appliance drivers that just pour in gas and drive it until something breaks - take your pick.

But again, with all the electronic controls being added to virtually every system on a vehicle these days, it's not outside the realm of possibility that a software bug or electrical fault could defeat all the measures we've discussed and actually prevent someone from stopping the engine and/or vehicle.

Personal experience - I've got an 05 Jeep Liberty diesel, with an electronically controlled 545RFE transmission. For a few months I tried using one of the Scangauge II displays hooked up to the OBD port. After starting to use the display, I had several instances where driving along at speed - anywhere from 35 mph up to 70 mph on the interstate - there would be a loud WHAM that shook the whole vehicle, the transmission would drop completely out of gear into neutral, and the engine would go to idle regardless of the position of the accelerator pedal - after 2 or 3 seconds, the transmission would start reengaging itself, until it was back in the proper gear for whatever speed the vehicle was still traveling at, and the accelerator pedal (drive by wire potentiometer affair) would respond again.

I had my local tranny guru hook up his high-end scanner to the vehicle, and he found several hidden codes where the TCM had completely lost signal to the data bus, and rebooted itself at speed.

The culprit turned out to be the Scangauge display - it was putting out so much noise on the data bus that it was occasionally causing the TCM to lose signal. Once I disconnected the display and stuck it in the closet, there were no further instances of tranny misbehavior.