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Discussion Starter · #1 · (Edited)
Hi, I drive an 04 645ci convertible, 100k miles, SMG trans.

It***8217;s at the trans shop because the transmission failed. All the symptoms point to hydraulic pump problems.

The shop has done an analysis and at this point has noticed that the relay which activates the pump is not receiving power from the computer at the times when the hydraulic pump is failing. At this point they***8217;re tracing wires to determine whether the computer isn***8217;t receiving the correct signals to initiate the hydraulic pump relay. This transmission shop does not seem to be certain as to their plan of action or path to full repair.


Has anyone had an electrical issue similar to this pertaining to the transmission, and if so, what was your experience with it an outcome?

Does anybody know any good transmission shops that are specialists with this sort of thing?

Thanks,
Scott
 

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I keep hearing the same story with that generation of SMG transmissions. Seems like it's very hard to diagnose.

For my friend's car, the dealership just started to replace the cheapest things first and kept replacing parts until it got solved.
 

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Hi, I drive an 04 645ci convertible, 100k miles, SMG trans.

It's at the trans shop because the transmission failed. All the symptoms point to hydraulic pump problems.

The shop has done an analysis and at this point has noticed that the relay which activates the pump is not receiving power from the computer at the times when the hydraulic pump is failing. At this point they're tracing wires to determine whether the computer isn't receiving the correct signals to initiate the hydraulic pump relay. This transmission shop does not seem to be certain as to their plan of action or path to full repair.

Has anyone had an electrical issue similar to this pertaining to the transmission, and if so, what was your experience with it an outcome?

Does anybody know any good transmission shops that are specialists with this sort of thing?

Thanks,
Scott
Go to the M5board sire & ask the guys with M6's. They will be able to help you better since a SMG is not very common to the 645 & 650's.
 

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Go to the M5board sire & ask the guys with M6's. They will be able to help you better since a SMG is not very common to the 645 & 650's.
Not a good idea, the SMG III from the M5 and M6 is a completely different system, not comparable with the normal 6-speed SMG in 645/650i.

On topic: how the repair shop wants to know at which times the pump needs to prime?
Normally it works like this: the SMG ecu monitors the pressure in the accumulator and activates the pump when the pressure is falling below a threshold. So if the guys from the shop are right si their theory I would suspect the pressure sensor.
 

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Discussion Starter · #6 ·
somewhat of a solution

Yeah I did. The hydraulic lines leak. One of them. It was hooked up to a computer and the pressure on one of the 3 lines was dropping slightly as the car drove. The system goes into failsafe mode when this happens. It goes into failsafe when the car is driven over long periods of time and the hydraulic fluid is heated up, hence thinner, hence more leaking. I've taken it to a shop or two.. They've fixed the leaks, but when the car is driven over a long long period of time in sport mode, say 2 to 3 hours, it won't go into reverse anymore, i've gotta push it. If i continue to drive it longer while it's hot like that then it won't accelerate from a stop easily. I had some college kids push me forward last night and then i parked it for 20 minutes and it drove fine. Basically the car runs great now. I would say it's at 95%, but if it gets heated up quite a bit then it won't do reverse, then possibly 1st gear if it's still driven. It's a heat thing. It has cost me about 2 grand to investigate and fix to the point it is at. It's in sellable condition now. drivabale well. So that's my experience. If i could go back i would probably opt for a manual trans.. but this smg trans offered me features like the paddle shifter and upgraded m6 steering wheel. I like it. So I'm working with it. I drive it long distances without fear now. I understand how it works and what the weaknesses are.
 

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Discussion Starter · #7 ·
I think that a big part of the diagnosis problem is lazyness. You have a car come in, it's this bmw 645. The first think shops want to do is hook up the scanner. then they see the codes and want to fix what part the code pertains to. Easy money, cut and dry. If it still has the problem then replace more... the guy driving the car shouldn't have it if he don't have the money to fix it. That's the way they see it.

You gotta have someone you can trust. And a little insight going into the situation. The dealer wouldnt' even hook up a computer to it. If they would have, they still wouldn't have identified the problem. You need someone willing to look at it on the computer and who will analyze the hydraulic pressures.

After the first guy did that for me, and it was leaking again, it was throwing trans codes of course... i sent the car to a shop that sounded competant on the phone and i told him straight up to ONLY fix anything leaking on the trans. I told him codes would go away after. Not to worry about them. So that's how you gotta approach it. It worked for me. People don't wanna diagnose that car because they're not familiar with it and they're looking at a project to properly diagnose it. I got lucky enough to meed a competent computer guy.

They fixed the leak the first time.. then a few hours later it left me stranded.. the hydraulic pump resevoir was leaking from the cap. The resevoir is plastic. The shop replaced that resevoir. By my logic the car probably is still leaking from hydraulic lines somewhere, but I'm not gonna go any further in repair. It's sellable and I'd drive it across the country without batting an eyelash. When i city drive it for hours or am on it hard it needs some time to sit that's all. I can live with that. And i've got a fundamental understanding of the trans should i need to go into a shop.
 

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Discussion Starter · #8 ·
Also I don't have a clutch and i have the luxury of gear control in any instance. It's a good experience overall. A little clunky? maybe.. but who has these transes? Nobody. It's cool.
 

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Discussion Starter · #9 ·
I got a ticket in Pennsylvania for speeding as i was slowing from hitting almost 150mph. I hit 147. Cop clocked me at 88mph on the decent. 400 dollar ticket
 
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