Trans Fail Safe Mode...yet another post..
 

Alright, I'm looking for some advice. Searched some post and i found lots of simliar issues but none quite like mine.

What happened: I was driving the car as usual came to a stop light and while waiting for it to turn green the car's rpm's dropped and it started to roughly idle. Also, I got the battery light and trans fail safe mode error. I drove cautiously as my destination was 3 miles or so. The car shifted awkwardly but it did shift. I figured this was the safe mode. Once I got to my destination I decided to turn the car off and on in hopes that it will clear my error codes. Well what i got was a little surprise. Codes remained and the engine wouldn't turn over. Eventually the codes did go away.

Diagnostics: Tried to jump it and nothing. Checked Batt voltage 12.0. I noticed that the car didn't seem to sense when I was in Park/Drive whatever gear the lights on the dash weren't changing. Tried to start in N and Park and nothing. I must say that if i put the car in Park it doesn't move and the transmission is engaged. If i put it in neutral it does go in neutral. I can see the shift lever under the car has a full range of motion.

Scanning the codes I found one engine code for o2 but I doubt this is related. The interesting one I found was for Transmission Range Sensor (i'm pretty sure that's what it said). This makes sense as the car can't tell its in P or N and it won't start.

What and Where is this sensor? Has anyone seen this before? Is this a waste of time because it means my trans is shot or is this a simple fix? I'm wondering if this entails dropping trans pan and changing sensors inside or if this is some place else. Any help will be greatly appreciated.

BMW Repair – BMW X5 P0720 and TRANS FAIL SAFE mode. Not sure if this is related.

So i talked with someone else they are pretty convinced its the alternator not the shifter position switch. Anyone else have any input.

probably battery light came on first, than the failsafe mode. i had a failure of the alternator and thats what happened. check the battery and see if voltage is lower than 13V than its the alternator

Had the same problem and it was the alternator, I actually drove about 70 miles before the Fail safe program came on.

ok.
 

Degree of difficulty replacing the alternator? Tried to see a DIY but seems pics/videos have been removed. I would think this should be kinda straightforward i don't have access to my car right now to see how buried it is but it looks like its on the top of the engine bay.

Where would you buy an new alternator? Right from the dealer or someplace else?

Thanks for the advice I'm going to charge the car for like 15min today to see if it tries to crank if it does then this is spot on. Thanks.

i tried to put a 50amp charge on the battery for like 15min and it still didn't turn over? This really an alternator or what? I tried charging it through the posts in the front.

I had a similar problem with my 4.4. I got a low tire light then a 4x4 light then the abs and brake light then the transfailsafe mode.

The dealer diagnosed it as a bad alternater sending spikes of voltage to mess up the computer system. 16.5 volts they said. They replaced the alternator and all was fine. But after not using the car for a few days the battery went dead. I put a charger on it over night and It barely started up in the morning. When it started warning lights were on again.

Bottom line was I tested the battery and it was bad. Weither or not the battery failure was caused by a bad alternator or or bad diagnosis I do not know. Dealer said they tested the battery. After I changed the battery everything is good again.

Gary

So you are telling me that it could of been the battery all along. I don't know if that's the case for me cause its about a year old. I suppose it could fail though. I'm planning on charging the battery overnight to see if i could rule that out.

What is strange to me is the car refuses to try to crank. No clicking sound, it just doesn't even try. When you put your key into position 2 right before the start position does your car show that the car is in Park? Cause mine doesn't know if the shifter is in park or neutral or any gear for that matter. It does recognize that i put it in sport mode though as the indicator light on the console reflects that change.

I'm desperately in need of help I have no car for a week almost and I'm not finding much hope here.

if i was in your position and i was with similar symptoms i would first swap alternator, which i did. that ended up being a culprit of the problem, i actually took a word of mechanic on this one and he made the right call.

Not sure if it is or not. After I charged mine overnight it would still start but the voltage on the battery was about 10 1/2 volts.

Snce our cars are computer driven with sensors sensitive to voltage this could easily wack out a system.

Try checking your voltage before you start should be 12 1/2 to 13.25 volts. Then check when your engine is running and it should be approx 14 1/2 volts (alternator charging). Or charge your battery and take it to get tested.

I never noticed if the park light is on in position "2" I will check that later.

Gary