Welcome to Tech Talk, where our resident BMW tech Nick Owen answers all your pressing BMW technical questions, frustrations, and issues. Have a question for Nick? Email him at techtalk@roundel.org. Let’s get into it.
Key Fob Saga
Thanks for your guidance and response to my 2007 335i key fob issues. I thought I would pursue your idea that maybe both key fobs have become unreliable over these years. Though double failure like that is unlikely, like you said, it’s possible. I’ll tell you a little story that might be interesting with these key fobs for this car, as it’s related to European delivery of this car as well as a heart procedure that I had done in about 2010. I’m sure they seem to be very unlikely events that could relate to this topic but here goes.
The European delivery in ‘07 was very rewarding and enjoyable. When I dropped the car in Paris for BMW to take for shipment to the U.S., I was instructed to leave one key fob with them and take one home. So, upon arriving home in Texas we drove from the airport to home in the Chevy Tahoe that we left at the airport, no issues. Well, BMW had some delivery problems and this car got lost in the system somewhere. so it took maybe three months or more to finally take delivery. BMW actually felt obligated to compensate us for the significant delay and gave us a one-month equivalent car payment refund by check, even though we weren’t actually financing the car. That was a nice gesture.
When the car arrived, we looked in the usual locations for the key fob that we had brought home and couldn’t find it anywhere. Due to the timing delay in the delivery, it was lost. So, I ordered a second—or I should say a third—key fob because you really need to have a spare.
Now comes the heart procedure wrinkle to this story. I needed to have this heart ablation done, which is a significant but minor surgery some years after buying this 335i. After the procedure and overnight stay, I was not permitted to drive for a few days, so my wife was driving this same Tahoe. I was in the passenger seat, which happens very seldom because I’m typically the driver. During our 30 mile drive to our house from Austin, I thought it would be useful to clean out the glove box in this Tahoe since it was stuffed full of receipts and various things. I started rummaging through those and the lost key fob from the European delivery was in the bottom of this Tahoe glove box. I placed it there on our way home from the airport and forgot it.
I’ve operated with the number one and three fobs for almost 20 years. When you suggested maybe both of these had gone bad I realized I actually have a practically unused third fob in the spare key drawer. I changed that battery and the key fob features came to life.
There was a slight wrinkle to this after the awakening of the system. The long idle number two key fob quit working and one of the others started working again, and only one of the three actually operates the car right now. Still a little bit mysterious, and not quite reliable for the long haul, but operable for now.
A long story, but I think it is a slightly interesting one . Thanks again for your suggestion. It might give me enough operability to not have to get professional help.
Jeff Kirk
Thank you for telling me the story about the Euro delivery mess up. That is ironically helpful because the only two “master” keys can be used for comfort access. The vehicle only allows for four “master” keys (fobs) to be active at a time, in case of multiple drivers for one car. The Comfort Access Module (CAS) has room for up to 10 keys to be used in its lifetime. If that number were to be exceeded, then the CAS module needs to be replaced to start over. That means any additional key cannot be used for comfort access features. You will have to hit the buttons to lock/unlock it.
If you used keys one and three primarily, then only key one would be working properly for comfort access. It might be wise to take all three keys down to the dealership or a competent independent shop that can get into the CAS module and check their health and operational abilities. They can also block or initialize a different key to be either a primary or backup.
Transmission Fluid for E39 M5
I have a 2003 E39 M5. The car has 9700 miles on it and I have owned it since new. It’s a total garage queen and I am having some refurb stuff done at the BMW Seattle (which I totally trust). My clutch died and the dealer is replacing the master cylinder and the slave cylinder.
In 2015, I had them replace the transmission fluid with Red Line. I had to source it. Now, 11 years later, I want them to change it and they are fine doing it, but I have to supply the fluid.
I don’t have a record of what I used, but it was whatever Mike Miller suggested. If memory serves (and I don’t trust my memory) it was ATF fluid for my six-speed manual.
I asked Claude.ai and it gave a different recommendation. It said “For your 2003 BMW E39 M5’s Getrag 420G 6-speed manual transmission, the correct Red Line fluid is Red Line MTL (75W80 GL-4).”
What is your advice? Also, should I replace the fluid in the differential? If so, what Red Line product for that.
Mike Nash
That Red Line fluid for the transmission is correct. For the differential, I would use the 75w-140 version.
