Another new guy, another diagnostic question

[Bond... Vagabon]

Hi everyone, been reading up, found symptoms of my problem elsewhere but not all together, so figured I'd start a new thread. Up until a few years ago, I was a diesel mechanic, specializing in engine swaps, putting fuel efficient little diesels in classic 4x4's mostly. I was "the guy" for tricky diagnostic stuff, too. Then I got multiple sclerosis and have some serious brain fog from that, so these forums/YouTube have been great for helping me do diagnostics that I used to take for granted. So thanks in advance, it allows me to wrench a little still, even if only on my own stuff. On to the problem

I have a 1997 or 1998 BMW 740il

Picked it up yesterday cheap, cause it "lacked power" sometimes according to the previous owner.

I can drive it around, no noises, if I go over a bump, it will sometimes flick a code 0740. If I start from a stop on a hill, it will sometimes throw a gear 2 incorrect ratio, and gear 5 incorrect ratio

never had it throw just 2 or 5, always both, despite pulling over one scanning immediately after it does it, so before it would touch 5th gear?

When it does any of these, from a driver's perspective, there is no noise, not even increased trans "wrrrr" volume, let alone "whine" or screeching. It acts like an old Chevy three speed, where the kick down cable is not adjusted quite right, and you are trying to accelerate up a hill, not enough power...then down shifts and zoom! Again, with no bad noises.

Goes highway speed fine, up to 70mph on rolling hills, with no rpm "hunting" indicating an obvious converter slipping.

My driveway is a measured 15° slope, which sounds not very steep, but if you looked at it, you'd think "dang that's steep" and if I stop in the middle, like to open garage door, then go to pull in, it will hold itself on the slope, or roll back a bit as I accelerator pedal then, I assume downshift? And then vroom! Zips up and I have to be paying attention not to end up in the kitchen.

P.o. had bought it a year ago, doing same thing, but throwing 0740 exclusively, it sat while worked on other projects, 4 months ago, he swapped out trans filter and fluid, I did a fluid change again yesterday, with the "max life" red jug stuff, that meets the 711____ BMW trans fluid requirement number. It seems to have had a slight improvement, as in slightly less likely to throw a code.

Oh, lastly, trans failsafe program goes back off pretty quick.

What all should I check? I believe previous owner has the round plug reader to read trans info, if that would give more/better data than my blue tooth reader and "torque" OBD2 app that I am using.

My current guess is that worse case I need a new torque converter, but the bump triggered fault, lack of slipping noises/burnt fluid, makes me think there could be electrical/sensor component to the problem?

Thanks again for any advice. I don't mind putting a new converter in, but hate diagnosis by part application on principle, even though I'm not as smart as I was before my brain started eating itself, due to the multiple sclerosis, hah.

Sent from my Nexus 5X using Tapatalk

[Bond... Vagabon]

Little update, now it drives all over without throwing the code, but then I turn the car off, and when I turn it on again, it has a code 0740. It does it pretty consistently.

Any guesses now that it is doing that? I've probably put 20-25 miles on it since it's trans fluid change. It deffinately has improved. It only now throws the 0740 when I turn it on, and has not gone into trans failsafe program, in that time, roughly 5x5mile trips.

Should I try another fluid change before jumping to the torque converter? Fluid and filter? Fluid, filter, and speed sensor?

Any advice would be much appreciated.



Sent from my Nexus 5X using Tapatalk

[shogun]

Moved to E38 forum

[Timm]

P0740 is a lock-up clutch electrical error, by that I mean that the EGS has decided that the solenoid responsible for operating the clutch is demanding too little current. And that makes more sense if you have a connection problem either at the gearbox or on the EGS. I would pop under the car and check the multi-way connector at the gearbox as a good place to start.

[Bond... Vagabon]

Thanks for the tip, it would be great if I didn't need to pull the trans. Is there is only one electrical plug on the trans? And where do I find the egs?

Thanks again, put another 20 miles on it today. My slight valve cover gasket leak seems to have cleared up on its own. I may have gotten lucky, and a few heat cycles softened up the seal, after it had been sitting for a year.

Other than the transmission code, I just need to figure out what is keeping the power seats from working, driver seat is max forward, and I am 6'5", hah. I'm amazed I can pretzel in. Checked the fuses, unplugged the driver seat switches, and replugged them, no obvious looseness or corrosion. It looks like I can undo two bolts and tip seat forward, I can't reach front Mount bolts to remove seat to easily see the bottom, so that is next best I think. Will put power to the motor and see if it's alive. Switches look brand new, but seat motors look old. The fact that neither seat has any power function working makes me think it is electrical confection somewhere farther along, after their harnesses join up, rather than the motors themselves.

And of course, here is a pic of the car.

Sent from my Nexus 5X using Tapatalk

[Mayorchuck]

Do your steering wheel adjustments work?

[Bond... Vagabon]

No, steering wheel power adjust does not work. Most of the other electric stuff works, trunk shut assist, backup dipping of power mirror, sunroof, etc. But no power seats, despite obviously new buttons/switches. Does that help narrow down what it could be?

Sent from my Nexus 5X using Tapatalk

[Mayorchuck]

Seat and steering both go thru the seat module.

https://www.bimmerforums.com/forum/s...us-Seat-Switch

[Bond... Vagabon]

Thanks for the diagram, should my e38 be the same as the e39 in that link?

If steering wheel adjust and both seats don't move, then I can start by assuming it's not the seat motors, and start from where those three things connect, and check between the battery and the junction the seats and steering wheel adjust split?

Is there a way to test that module, I have a scan tool that is a little better than bare bones OBD2, but not much, it lets me see injector balance, that kind of thing. It uses a blue tooth reader, and the "torque" app.

Plan for tomorrow is to disconnect and clean the plug from the harness to the trans,

check all fuses for corrosion/if blown.

Undo two bolts for seat base tilt so I can jumper the fire and aft seat motor, and get it back enough so I can remove the seat and trouble shoot this stuff easier.

Does the seat module have its own fuse? I checked 15 and 16 which were supposed to be for the seats, but they looked good.

Sent from my Nexus 5X using Tapatalk

[Mayorchuck]

E39 seats are the same. Driver seat module is fuse 15.

[XAlt]

Remember, there's fuse blocks under the car that can corrode out because of water buildup. Number 3 cause of failed power seat\steering adjustment.

[Bond... Vagabon]

Where do I find those?

Sent from my Nexus 5X using Tapatalk

[XAlt]

Where do I find those?

Sent from my Nexus 5X using Tapatalk

By lifting the seat and front carpet up.

[Bond... Vagabon]

Ahh, I read about that one. When you said under the car, I thought you meant uuunder the car. So for fuses, there's box by passenger hood hinge, under passenger seat, glove box, and trunk right? Any others?

Sent from my Nexus 5X using Tapatalk

[Mayorchuck]

No fuses in glove box. Just relays and modules behind it. If you have a multi meter, check to see if you are getting 12v to fuse 15.

[Bond... Vagabon]

Will do, couple honey do list things, then I can get cracking.

I also have the apparently common "super cold air out of a/c but low volume, which goes to nice high volume of air after I've been driving for a bit" problem, so will be checking the actuator over the drivers pedals too. In my reading, it appears that if this is the culprit, it can be removed, restoring fill a/c air volume, at the loss of fresh air option.

People report they fail, cause the aluminum corrodes, has anyone tried to disassemble and clean one? I used to be a machinist before I became disabled, I may take a stand at it if mine is confirmed a dud. For the good of the order. I'm here in high humidity Texas, and things do corrode, even just sitting around.

Sent from my Nexus 5X using Tapatalk

[Bond... Vagabon]

Got the a/c working properly, hooray!

The actuator above the go pedal was unplugged. Plugged it in and good to go.

Started pulling trim off the front seats to be able to pull them and fiddle with power seat mechanisms more easily, as well as clean up connections under the carpet. These under seat fuses are just on the passenger side, correct? I sure hope so, not sure if I can get driver's seat out, while it's all the way forward. It covers 2 of 4 mount bolts. My idea to undo hinge bolts for seat bottom tilt is a no go. One is captured by trans tunnel.

I disconnected the trans computer connector at the computer, to look for corrosion. It is the smaller one, between the two larger ECM looking things just aft of the under hood fuse box right? I will take for test drive tomorrow to see if it cleared up the trans codes. If not, I'll put it up on stands and check the plug at the transmission for corrosion.

I checked the battery again. 12.61 volts after several short drives, then sitting for 5hr or so. Cleaned the battery connections again, for luck. Made sure they are snug.

Is there a ground up near the drive train computers I should clean up too? I saw one that goes into the harness near where the harness goes into the computers.

I made sure to disconnect the battery before I screwed with the trans computer connector.



Sent from my Nexus 5X using Tapatalk

[oldroller]

Good work! Also on the AC system make sure the interior filter(s) are clean. In 'auto' the air volume can fluctuate from low to mid volume if the filters are restricted.
Check the main filtration under the hood also.

[Bond... Vagabon]

Thanks, down here in Texas this time of year, a/c is mucho nessicario. Clogged cabin filters were my first guess, cause of the intermittentness of the air flow, but the ones on the bottom of the hood are clean as a whistle. There aren't any others I need to check are there?

Sent from my Nexus 5X using Tapatalk

[Bond... Vagabon]

Argh, I can drive all over the place, without throwing p0740, as long as I keep it below about 2000rpm in 1st and second gear. But then I take it to the emmisions inspection station, and with no check engine light, they hook up their reader, and it throws a "pending 0740" code, throws the check engine light. Then I can hook mine up and it shows an 0740 code. Is this from not doing the "drive cycle" correctly after clearing a code, in order to reset everything?

Sent from my Nexus 5X using Tapatalk

[Bond... Vagabon]

I fixed it! Thought I would post an update. I was fixing a rear turn signal that had stopped working cause a corroded ground, decided to clean up the battery positive connection to the transmission, trans slipping trouble code problem is 95% better, passed emissions testing too. I can still get it to slip/throw a code if I park on my steep driveway, then try to accelerate up hill, but normal driving it does great. Can romp on it a bit, all good.

Sent from my Nexus 5X using Tapatalk