trans fail safe

[sparkshaneman]

Hello. Received this message for the 2nd time this weekend. Driving on the highway w/the cruise set at 62, received the CHECK light on dash and trans fail safe on the MID. Pulled off the highway, as the car began to run sluggish. At the stop light, I tried putting it in 1st gear (thought I had read somewhere to do this) and I noticed I had nothing displaying in the gear selector box on the dash, expecting to see E D, or S 1, S 2.... Pulled off on a side street and turned the car off and sat for 5 minutes or so. Started it up and it was like nothing ever happened. No CHECK light on the dash or in the MID and the gears were displaying on my dash. Drove the car the rest of the weekend for about 60 miles and no issues.

I've received the trans fail safe error a total of 2 times now, owning the car for 4 months. Both times it's been on the highway. I drive 90% of the time in the city. Wondering if driving at a higher consistent speed has anything to do with this? Why would my gear options vanish?

thanks,
Shane

[shogun]

Clean the trans shifter switch under the console, when you see no gear in the mid, see details on my website below
http://twrite.org/shogunnew/topmenu.html
on the left click other BMW model, and then click E34 transmission

[sparkshaneman]

Thank you for the reply and instructions. Are you saying that this "dirty switch" can throw the trans fail safe error or do I have 2 separate issues going on here?

[cartoonz]

Pull the codes. Chances are that you're getting an engine code which is triggering the trans safe message. The 850's do this

[Mikekugel]

Hello. Received this message for the 2nd time this weekend. Driving on the highway w/the cruise set at 62, received the CHECK light on dash and trans fail safe on the MID. Pulled off the highway, as the car began to run sluggish. At the stop light, I tried putting it in 1st gear (thought I had read somewhere to do this) and I noticed I had nothing displaying in the gear selector box on the dash, expecting to see E D, or S 1, S 2.... Pulled off on a side street and turned the car off and sat for 5 minutes or so. Started it up and it was like nothing ever happened. No CHECK light on the dash or in the MID and the gears were displaying on my dash. Drove the car the rest of the weekend for about 60 miles and no issues.

I've received the trans fail safe error a total of 2 times now, owning the car for 4 months. Both times it's been on the highway. I drive 90% of the time in the city. Wondering if driving at a higher consistent speed has anything to do with this? Why would my gear options vanish?

thanks,
Shane

The first thing to check are your spark plugs. NGK BKR6EK plugs are the correct 1000 ohm resistor plugs. They are spec’d for the 840 V8, and are one heat range colder than the original V12 plugs that are no longer being produced. You can buy them at Oreilly’s, Autozone etc. Try installing on cylinders 6 & 12. These are the plug wires that have the sensors to detect ignition pulses to give the DME computers cam positions. Check your caps and rotors as well. If this doesn’t solve your problem, then you will most likely need to clean the armatures and brushes of your throttle bodies. I know it sounds strange that the transmission could be affected by such things, but many things interact on our 850’s. There are some tutorials if you search throttle body refurbishment, OR, you can contact Dragon850 and he can go through them for you. Good luck!

[shogun]

wrong spark plugs will not cause this

I had nothing displaying in the gear selector box on the dash, expecting to see E D, or S 1, S 2..

it is an electrical problem. From my experience I would start with the trans shifter switch

more pics of defective shifter switches http://www.bimmerboard.com/forums/posts/744694/
"Disappearing or Momentary Shift Indicator LED in gauge cluster: Unless the LED is burned out (unlikely) they can be restored by cleaning the shift selector contacts. Remove the switch (set the handbrake & position the shift lever vertical, I think that's in neutral) Photo-4. Pry the switch open & clean the traces. I used 1000 grit ultra fine sandpaper with a little WD-40 & then cleaned it well & sprayed contact cleaner/lube on it. Photo-5a & Photo-5b. Bentley states this switch could be the cause of transmission problems as well:
Excerpt from Bentley's pg. 250-4: "A faulty gear position/start disable switch may cause transmission shifting problems and erratic transmission operation"
http://www.nmia.com/~dgnrg/page_13.htm

[sparkshaneman]

Thanks everyone. Now I know where to start. I'll provide an update, once I start working on it!

[JDP530]

i bought a car that was not running at the time of purchase so I had planned to go completely through the fuel system, engine electrical system, and reseal intake gaskets. I put the car on the road and it would run great most of the time but I also experienced the exact same problems you have losing power around 60+mph, occasionally going into trans fail safe mode, etc. I could stop and restart the engine and it would run fine again but eventually go into power loss mode sometimes within a few miles or 20-30 minutes.

I had installed new plugs, new aftermarket wires with CIS (sensors) on plug wires, new caps, rotors, etc. Well, I chased this engine running fault for a couple of months and finally determined that problem was caused by the aftermarket sensors installed on the new sparkplug wires I bought from a very well known vendor who races BMWs. I also contacted the manufacturer of wires sold by vendor and they had no idea why the sensors were faulty. Anyway, after trying a couple of other brands of sensors, I eventually installed wires with BMW brand sensors and fault went away.

[xeler8]

I would consistently get the Trans Fail Safe with my 840i. Turned out it was a fowled MAF that would trip the error code at higher RPMs.

[sparkshaneman]

removed the shifter to clean and found something interesting, upon removal.shifter.jpg guessing a mouse found a little home?

[rjjablo]

Be careful because they break, I would pull the entire console and look for other damage like chewed wires etc