Random Downshifting

[Thumper540i]

I am new to BMW's and have been reading these great forums.

I just bought a 2002 540i with the Automatic Steptronic and love the car. However, I am noticing that the transmission will randomly downshift. No change in pedal position then it just downshifts and a couple of seconds later it will go back to the correct gear.

My thought is that the kickdown switch may be faulty or tricking the transmission that the pedal is fully depressed. Others have stated that I may have low transmission fluid. The previous owner did have a reciept back in Feb of this year where the torque convertor was replaced, maybe they did not check the tranny fluid correctly and it is low? Something I plan to check this weekend. No abnormal check engine lights or anything on the dash controls either.

I did a search on the forum and did not find a solution or discussion on this. Maybe I searched for the wrong text but to me it is a random downshift while driving.

[rf900rkw]

It will not be fluid level. Nor is there a kickdown switch. The first thing that needs to happen is to figure out exactly what is happening. Is it really downshifting? If so to what gear? Or is it just releasing the torque converter and then picking it back up? Once this is determined, then you can start looking for the cause. The two things I can say is the problem will not be inside the transmission, and it is very likely the problem won't even be anything directly related to the transmission.

[Thumper540i]

Thanks for the reply.

It is for sure down shifting. I know this because i put it in manual mode, had it in 5th going around 50mph, and it downshifted to 3rd without pressing on the gas, then a few seconds later i was able to shift back to 5th.

I thought i did have a kickdown, i can feel it click. when i press the pedal to the floor

[rf900rkw]

Well there is a big piece of evidence. 5th-3rd, even in manual mode. That's not the transmission going rogue and shifting down (which it can't do, anyway...*Something* is really pissing a computer off, somewhere.


There is a detent to simulate a kick down point, yes. That way the feel is consistent with the older models. But the actual signal is provided by the electronic throttle system on the M62tu.

[Thumper540i]

Hmmmm. Not sure where to start with that. With no light on I really don't even know where to start.

Is there a way to reset all the computers?

[gjVah]

Find a good reputable shop in your area that deals only with BMWs and have them take a look at it. They can diagnose and tell you exactly what's wrong with the car and you can DIY it yourself to save money (if that's what you have in mind).

It will be cheaper than replacing random parts until you find the problem, and you'll be glad you did it in case it turns out to be a time sensitive issue. (knowing exactly what the problem is before it becomes worse and damages more stuff).

Computer diagnostics is not expensive, just make sure you find a really good shop that knows old BMWs. (check Yelp and Google Reviews before you take it anywhere)

[rf900rkw]

Gather as much data as you can about when/how it does it. What speeds, temp, even curves. Even if you do take it to a shop, they'll have to be able to duplicate the problem, and the easier they can find it, the quicker/cheaper the diagnosis.

[Thumper540i]

Thanks for the help. I have never taken a vehicle into a mechanic before. always do my own work. This will be very awkward for me;) but i will take your advice and head down that party.

[rf900rkw]

Even if you do take it in, and I'm not saying you should... yet.

Get as much data on the triggering condition as you can. It will help you / us / mechanic narrow things down.


Get ye to the "Diagnostic Software" forum here, and start reading. You want to build yourself a working INPA system. This is a factory scanner system that has escaped into the wild, and people have figured out how to interface it with cheap Ebay cables. $20 and a bit of work and you have a one of the better scanners for this car.

[Thumper540i]

Fantastic, i have not started reading that section yet but will start tonight. I have a obdi2 cable i use on my other cars. I will have to read up and see if i can get it to work.

[Thumper540i]

Alright, I have been collecting data on when this occurs and thought I would post before taking it in to have it looked at to see if there were any new ideas.

It has downshifted in all three tranny modes. Standard drive, Sport mode and manual mode.

It has happened going straight with no incline, up a hill and down a hill.

It has happened with slight acceleration, not enough to kick it down and has even happened while letting off the gas coasting.

It has happened at 50 degrees and at 90.

I drive 11 miles to work each way and I have driven to work and it does not happen once and other times it has happened up to 5 times.

One last bit of information. When it happens I can hit the gas and still kick it down another gear. This is really the most random issue I have ran into. I'm almost thinking a bad sensor feeding the computer the wrong info.

Will disconnecting the batt reset the adaptive transmission memory?

[Thumper540i]

Just wondering if there is any negative effects with disconnecting the battery other than random clock and preset settings.

[514mach1]

RF900r is usually pretty sharp on this stuff, but have you checked the fluid level? I kinda doubt it is fluid level but to me it's one of those first things to check before anything else. One of the other obvious things to look at is the wiring harness going to the transmission (any rubbed wires grounding on something) and the pins (corrosion).

[rf900rkw]

Ah sorry... I missed the previous post.

Disconnecting the battery *may* clear out the adaptions. I'm still not totally convinced it can be done in a reasonable time, but if it does, it will wipe all the adaptions. The one that will bite you is the throttle. Be prepared to do a throttle relearn. Key on for 20 sec, off ofr 20 sec, then start.


And yes, the computer is reacting to garbage input from somewhere. But man is it appearing to an elusive random thing. As I mentioned in another thread, a flakey TFT sensor can cause the computer to do uncommanded shifts. But the sucker isn't very cheap and replacing it requires some serious work (replacing the entire internal transmission harness).

I'm really going to have to suggest you put together a scanner rig if you want to dig in. INPA is available for the download and a $20 cable. It will be able to read transmission codes, live data, and reset all adaptions.


RF900r is usually pretty sharp on this stuff, but have you checked the fluid level? I kinda doubt it is fluid level but to me it's one of those first things to check before anything else. One of the other obvious things to look at is the wiring harness going to the transmission (any rubbed wires grounding on something) and the pins (corrosion).


The fact that the display shows the commanded gear, shows the downshift, says that the computer has broadcast the information on the CAN bus (or is it on the k-line?). That tells us it is a computer decision and not a random artifact of an external failure. The computer is reacting to *something*.

[Thumper540i]

Just wanted to post an update incase others are following or have the same issue.

Unhooking the battery overnight did not help.

Continued to log when, where and how it happened.

Started to put the diagnostic software on my laptop and ordered a cable.

But I could not wait any longer so I finally gave in and took it to a well known tranny shop here in Columbus, OH. They hooked up their tool and found out that the Transmission Temperature sensor was showing a 25°F swing in both directions and thought that was the cause. I could not argue with them as it was just sitting there idling.

They gave me a price of $250 for the sensor harness and $250 for labor and $150 for tranny fluid. My intuition says to do it myself but im only going to save $250 for digging into the one area on a car where I am not an expert and this guy is a master tech. I think Im going to have them do it just wanted to get your opinions on the following...
A. could a transmission sensor cause random downshifting
B. If so would you do it your self or have someone else do it for that price?

Thanks!

[larrym3711]

You need some experienced help. I can tell you that the temperature sensor for the tranny can (on:some cars) keep the tranny from shifting to higher gears as it thinks (rightly or wrongly) that the temperature is too cold and keeps the tranny in a lower gear whilst it is cold.

larrym3711
2001 540iA Sport

[rf900rkw]

Yes, most definitely this could be the problem. This is the type of thing you will find in minutes with the proper person behind the right scanner. Or you can find it in hours by swapping the whole transmission, as too many places would do.

I, of course, would change it myself. But that's just me. <GRIN>

The temp sensor is part of the wiring harness. BMW does not sell it; you have to go through a ZF distributor. It can be changed in the car. I'm pretty sure it can be done without pulling the valvebody, unlike the '19. Fluid is your choice, ranging from say $8 - $20 a quart, and you'll need 6 to 8 quarts. Do the filter and pan gasket while there.

[Thumper540i]

Alright, ordered the parts and after some research and rf900rkw comment I decided to do it myself. I have rebuilt TH350 transmissions in the past but I know this transmission is a whole nother level.

So my question is now that I am doing it myself and saving about $400 should I go ahead and replace anything else like the pulse generators? Currently I have the harness, filter and gasket on its way but thought if I have it open what else is a common failure component?

This next comment prob resides in the diagnostic software section but its quick...I have a cable and a program called diagnostic that is able to connect to my 540i but it only gets engine data. When I tried carsoft I get a cable error. I am guessing it requires a special ODBII cable and not the generic one I have?

[rf900rkw]

Yes, you need a special cable. The most common used with INPA/DIS is the VAGcom KKL cables available on ebay and the like.... and these require modification to work with BMW.

Solenoids and pulse generators just don't give any problems on these. The temp sensors aren't a big failure item, but not unheard-of.

[Thumper540i]

I really appreciate all your guys help. Got the new harness in easy as pie, I did not even have to remove the valve body. The only problem I had was a stripped out torx bolt on the pan, just used an easy out and got another at Sears.

Here is my problem...I went to the local BMW shop to get the correct transmission oil, even gave him the BMW part number 83 22 9 407 807. They did not have it in pre-packaged bottles so the parts guy said I can go get some from one of our 50 gallon drums in the service shop. So I agreed no problem right...? Well, the stuff that came out of my transmission is redish like most transmission fluids however, the new stuff I got from BMW shop out of the 50 gallon drum looks and pretty much smells just like motor oil, it is definitly not red.

Like I mentioned in my first post I am not a BMW expert but I have one of two problems based on my logic. Someone put the wrong fluid in my transmission prior to me having it or the BMW shop gave me motor oil and charged me $25 a liter:help

[Thumper540i]

Looks like the BMW Stuff is suppose to look like regular oil. I went ahead and added it in and it runs great, no downshifts at all on the short drive I took it on.

I hope that it is OK to mix the two together. I am going to drain and refill once a month until I get it clear, instead of the redish brown mix color it is now.

[robsbmwx5]

Hi have a 2004 x5 does a simular type of changing gears mine is flat road and holding speed at 60kph o 65 kph all up to about 80kph over about 85kph its ok but in the lower speeds seems to change to 5th to 6th and than back to 5th etc with gaining any speed just changers gears up and down had it to mech shop and no fault codes at all anything over 85kph is ok say sitting on 100kph dosnt do it would mine have same prob please help

[rf900rkw]

You have a different transmission in a different vehicle with similar but slightly different symptoms. While it could be the temp sensor, anything from a dodgy MAF to slightly different tire sizes could also be the root fault.

[Spirit Force]

As rf900rkw said you got totally different situation, since you got different vehicle with different transmission. Get it properly diagnosed or buy INPA cable and start digging in. The worst solution is to start randomly throwing parts at it.

[videoholic]

I just bought my 2009 335i a couple days ago and holy cow I had this happen to me tonight. I had just driven about 15 miles extreme rain (Florida during Isaac) and I'm on a straight road in automatic trans I was probably in 4th gear going 40. Cruising and all of the sudden the dash said M3, then M2, then M1. Engine reving hard. So I put it in manual and down shifted. The car was fighting me. Kept trying to upshift while I kept downshifting to try and get to where I could pull over and not have the car rev too high. It was very scary.

I'm going to call tomorrow and get the car into them, but dang I'm scared to put it out on the interstate again.

[SwiftSmooth528]

Kept trying to upshift while I kept downshifting to try and get to where I could pull over and not have the car rev too high. It was very scary.

I'm going to call tomorrow and get the car into them, but dang I'm scared to put it out on the interstate again.

Just remember, if it downshifts on you and begins to rev too high, just bump the stick one notch forward to get it in neutral. I guess you'd have to be ready to do it quick, though.

_____
Off topic, can you believe how many idiots are having their vehicle accelerate wildly to above 100 MPH on the interstates these days and all they can think to do is 1) jump on their cell and call somebody to ask what to do while 2) standing on the brake and maybe 3) yanking on the emergency brake?

Just pop it in neutral, idiot!

[videoholic]

Turned out they had done something with the steering column before I bought it and the paddle shifter plug didn't get seated correctly. Whew. That was a happy fix....

[mchua1971]

Hi, I am a new user.

I have a 2004, E63, 630i, Japan spec. I am experiencing problems when engaging manual transmission either in normal or sport mode. The car is being looked at by a transmission specialist who is struggling to sort it out too.

The problem is that when I engage manual transmission & work myself up to 3rd gear it occasionally upshifts the gear by itself rapidly to 4th, 5th & 6th gear. My RPM when this happens is only at about 3000. It has even happen in corners so its very dangerous to lose torque & control of the car.

There is no set pattern & this happens randomly. The upshifting can also occur if I am in 4th gear.

The peculiar thing is that this "self upshifting" only occurs on flat roads. It does not happen when ascending or descending hills.

No faults in the car nor on the diagnosis computer at the workshop. Mechanic has already ruled out (by transplanting from other cars when necessary) gearbox, gear shifter, DME system, Mechatronic, tyre size issues, ABS. Software already updated to latest version.

We are now investigating if the lateral & yaw sensors under the drivers seat could play a role in this problem but are still waiting on parts.

Has anyone had such an experience?

Thanks.

[shortedaman]

First your in the wrong subforum. Second i dont believe manual transmission cars can shift themselves.

[AK_5eries]

Excellent thread. Thank you thumper540i for excellent documentation and randy for his genius awesomeness.

Randy, a question: Can you spare me a link for a good place to download the INPA software?
Thanks

[mchua1971]

First your in the wrong subforum. Second i dont believe manual transmission cars can shift themselves.

Sorry for this. The guys in this thread seem to be best suited to help me out & I am desperate to solve the problem.

Car has both manual & auto modes.

[rf900rkw]

Mchua -- I'm assuming this is a 6HP26? It is not a transmission fault. I would first look at the mechatronic. Since your guy has already done that (replaced), then it is likely something is sending an invalid signal down the wire. Finding such can be a pain, and I really have no idea where to look. This is an unusual problem, for sure. My primary thought is something with the valvetronic system asking for a higher gear. But that is purely a hunch.

We see these units regularly as they are also in Fords. But I somehow doubt that Lincoln Navigator owners are constantly driving in Steptronic mode, so even though it's the same unit, the conditions aren't the same. How often does it act up?


Greentiger -- check the diagnostic software forum. I built my systems a few years ago. I understand the state of development has improved a lot since then. The site I used to download the software is no longer on the web... thanks to the feds. :)

[mchua1971]

[QUOTE=rf900rkw;24998490]Mchua -- I'm assuming this is a 6HP26? It is not a transmission fault. I would first look at the mechatronic. Since your guy has already done that (replaced), then it is likely something is sending an invalid signal down the wire. Finding such can be a pain, and I really have no idea where to look. This is an unusual problem, for sure. My primary thought is something with the valvetronic system asking for a higher gear. But that is purely a hunch.

We see these units regularly as they are also in Fords. But I somehow doubt that Lincoln Navigator owners are constantly driving in Steptronic mode, so even though it's the same unit, the conditions aren't the same. How often does it act up?

Dear rf900rkw,
Thank you for taking the time to post a reply. I believe it is a 6HP26.

How do we trouble shoot to check the valvetronic?

This problem occurs every time I drive in manual. It may take 2 minutes or 20 minuted to act up.

I also noticed that in auto mode my car is acting up. When cruising at 80kmh, 3000rpm, it often "hunts" for a lower gear without me adjusting the accelerator. We thought it to be a torque converter issue but my mechanic says that's not the problem.

More than 10 transmission "guru's" have had a look at my car including 2 who flew in from Australia & they too are baffled. My car may become a case study!!

Could the lateral & yaw sensors play a role? This thought came to mind because my problem does not surface when climbing hills or going down hills. We noticed that the lateral sensor was warm to touch, which we thought to be unusual for just a sensor. Awaiting the parts.

More information >
- TFT sensor changed
- MAF checked

Any other sensors we missed out?

Thx.

[BD40]

I know this is an ancient thread, but does anyone know if the original poster (Thumper 540i) got his random downshift fixed? He was going to replace the trans temp sensor/harness. I have the same symptoms and hope to have the temp sensor tested tomorrow. If it's bad, I'll replace it. If there's more to be done, I'd like to know.

[Micahlap]

Hello, I know this thread is very old but i have a 2000 540iA and im having a random downshifting issue from 4th to 3rd usually. It has happened a few times. Reading this thread i saw someone mentioned the transmission being too cold. I recently put in an 88C thermostat to help cool the car better and I’m wondering if that could possibly be the problem? The car has also jumped from 4th to 3rd to 2nd and it has also gone from 4th to 3rd and back to 4th and then back to 3rd while in manual mode. When it did that, the screen on the cluster said it went from 4th to 3rd to 4th and then stayed in 3rd. It isn’t happening super often and I’m noticing that it usually happens at night and not during the day and I’m also wondering if that could be caused by the temperature difference? Anyways if anyone can help, it would be awesome.
Thanks!

[TiesTorN]

lol... you could create a new topic.

your trans temp sensor is gone. replace the harness.