Two problems related to automatic transmission have been reported for the 2003 BMW M3. The most recently reported issues are listed below.
1. I live in lancaster, CA and when the summer comes around it get's really hot really quick. My BMW M3 2003 which happens to be an smg keeps having problems with the transmission. It causes my transmission to function improperly by shifting to "neutral" automatically. Today, on my way back from work I almost got into an accident when my transmission change automatically from 3rd gear into neutral almost causing the vehicle behind me to crash onto my vehicle. 2. The smg light keeps turning on. I took it to the mechanic immediately and he told me it was the "hydraulic control unit (hcu) with pressure accumulator" which is causing this problem. I notice this problem happens usually during the hot weather since it also happened to me last year around the same time. My BMW mechanic told me this would cost me on or about $3,000 with parts and labor. I got online as soon as I got home to see if anyone else is having the same issues as I am, found out that there are many other BMW M3 smg e46 (2001-2006) owners that are going through the same problem. It's consequences are that since this is the only vehicle I have, I feel my life and the safety of others are at high risk if my transmission changes from any gear into neutral while operating the vehicle causing a major accident to occur. 3. Nothing has been done to correct this malfunction. From what I have read and discover online, BMW north America knows about this issue and wants all BMW M3 smg e46 owners to replace the entire hcu which as stated before cost on or about $3,000 with parts and labor. This will only fix the problem temporarily since the problem will persist as the weather continues being above 85-90 farenheit. I don't believe is fair for all BMW M3 smg e46 owners to pay such amount when clearly won't fix such problem. It would be fair if BMW took charge and recall this issue that is putting every citizen in danger due to their mistake in the hcu for all BMW M3 smg e46 vehicles.
As you remember, we all spent about six months this past summer figuring out why our e46 M3 smg's were randomly throwing on the transmission check light and randomly cycling into neutral for aruond 6-15 seconds, displaying a constant "0" during an up or downshift in hot and/or humid weather. We determined after plenty of research and physically removing the smg's hydraulic control unit(hcu), and comparing hard-to-find blueprints of the unit what the malfunction was. The problem was the hcu's hydraulic fluid temperature sensor, which would go bad due to a thin-layered resistor inside the sensor that would microscopically bend and contract over time in avid heat/humidity situations, and send false data to the car's transmission control unit, giving it the illusion that the hcu was overheating and needed to be shut down. To this day, I am still puzzled as to why BMW would program the control module to do such a thing, knowing it would temporarily mame the car's ability to accelerate and/or maintain speed, and thus endanger it's occupants and the safety of other motorists around it.