Trans Fail Safe

[joeboch348]

Was driving down the highway and the truck goes into failsafe mode.. Not good on a 5 lane 70mph highway and being on a bridge with no breakdown lane..

Nursed it off the highway, Shut it off. Restarted it and drove it home without incident. UGH

Now I'm afraid to let anyone drive it.

Ideas?

I bought my 02 X5 4.4 new. Never abused, always breaking. I love and hate it at the same time.

[andrewwynn]

I had the same thing from a low voltage incident. First if it goes to failsafe it just goes to 4th gear and stays there id confidently drive maybe 40 miles or so to get home vs tow. Second get a real time monitor of voltage and see if you get any voltage dropouts. Usually the abs will "trifecta" on you before trans failsafe but I have had trans failsafe first that cured after a couple restarts.

In my case the B+ nut fell off my alternator I just refurbished and apparently didn't tighten.

So don't panic more than likely a computer glitch from voltage flicker than anything else

[scourtaud23]

I've had it a few times, either when before changing my battery if I let the car sit for too long, despite starting up, it wasn't happy or when I played too much with diagnostics and coding software without the engine running.



I'll admit its been a few months since its happened but I have been playing less with software and got a new battery... I'm not even sure it happened in 2018.

[srmmmm]

Clean the harness connector at the transmission and repack it with dielectric grease. It's quite possible road salt and debris has contaminated some sockets and pins.


2002 X5 3.0 344,300 miles
2014 428i 39,000 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles


1970 Firebird Under restoration

[Fifty150hs]

Check your alternator output and battery voltage. Alternator running, if it isn't 13.4 or better you have a bad or dying alternator. Battery with car off. Should be showing 12.3 or better. Let it sit and then check the battery again. If it has dropped significantly, likely you have a bad battery. I'm betting you have a dying alternator. Just went through the same symptoms with my X. Checked the alternator and it was only putting out 11.4 volts. These cars are very voltage sensitive and if it gets too low they start doing all kinds of crazy stuff, including going into trans failsafe mode.

[BAX5]

Wanted to post my recent battle with this for others reference.
I just replaced coolant overflow tank. During repair I disconnect intake plastics and intake air filter box.

Long story short, I failed to tighten the clamp right after MAF at air filter correctly. A few days later I got Engine Safe Mode light which cleared on restart. Next day I got the Trans FailSafe Mode light which persisted for the week.

I did all the things mentioned in these forums. (check trans ECU box for corrosion, clean connectors there and at transmission (which was dirty / wet externally). Check battery and alt systems. All good.

Fixed by dealer for $135 to reset the trans ECU.
They got me in same day I called so I'll take the hit.

Funny the trans has always sifted flawlessly (only 1 trans service done) but the FailSafe Mode is rough and nasty. I was getting all gears but shift down to 2nd and 1st was horrific. Not safe mode at all in my opinion.

[andrewwynn]

I had virtually identical shifting 2-1 slam and got failsafe and when I read the codes it said it was solinoid error.



It was a dirty cannon plug at transmission. I'm sure that's what your problem also was.

Did you ever have the symptom of dash indicator not match the gear selector?

I did not figure out how water got into that connection since the rubber boot is definitely water tight. It almost felt like the water comes down the inside of the wire bundle so I left my rubber boot open for now so any new water can drip out.

I plan to fill the boot with silicone and figure out some seal for the connector which may not have one. (or if I determine water does come from under the hood through the wire bundle I'll cut a weep hole and the silicone in the boot will force it to drop out not go into the connector.

About 1/2 oz. of very rusty water came out of my connector when I removed it !

[omodos]

Battery....I had this a couple of times each time it was my battery, both cases was me on a longish drive with all peripherals going air cond...radio etc etc (alt was pumping out enough mind you) and on charging up and driving again was fine

[brucemillar]

I was told by BMW that this was / is a known issue with the battery. Mine used to do it when the truck was parked for a few hours facing up hill? BMW said it was a plate in the battery shorting and the ECU defaulting to it lowest level of fault to “protect” the car?

Who knows? But a new battery and I never had the fault again.


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[jac]

In my case it was a bad MAF. I tried to cheap out and went with a cheapo one at first and that fixed the transmission/shifting, but it threw a bunch of other codes, so I just went and bought the Siemens and all is good.