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2003 325i (M54B30 swap)
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Discussion Starter #1
Hi all.
I posted previously thinking that my issue with my car going into trans limp mode was caused by an air leak (evidenced by codes p0171 and p0174). I yanked out the entire intake down to and including the lower boot, and I found no leak. Therefore, I'm assuming that the limp mode is being triggered by a fault in the transmission itself. The codes that are being thrown that relate to the trans are p0700, and after limp mode has been triggered p0735. Limp mode only triggers after driving for 10+ minutes, usually at 50+ mph. It resets when the car is shut off. Until limp mode triggers, the transmission seems fine, i can shift in and out of 5th gear without issue. Smooth, firm, fast shift, or at leas no more inconsistent than the other gears. So I'm assuming that the transmission fluid must be low (it's an auto, with a GM box). I've found a few conflicting reports on how to check it, some saying the car must be on, others that it should be off. Some say if you loosen the fill plug, fluid should dribble out, others say to stick a finger and wiggle to try to feel for fluid (That makes me a bit nervous :p). I guess the question I have is if anyone has any input on if this is really a trans issue, or a wild card somewhere else (i.e. pre-cat O2 sensors?) and also if anyone has an official, or proper way to check the transmission fluid.
Thanks for the help!:thumbup:
 

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E39 E90 E46 F10
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Hi all.
I posted previously thinking that my issue with my car going into trans limp mode was caused by an air leak (evidenced by codes p0171 and p0174). I yanked out the entire intake down to and including the lower boot, and I found no leak. Therefore, I'm assuming that the limp mode is being triggered by a fault in the transmission itself. The codes that are being thrown that relate to the trans are p0700, and after limp mode has been triggered p0735. Limp mode only triggers after driving for 10+ minutes, usually at 50+ mph. It resets when the car is shut off. Until limp mode triggers, the transmission seems fine, i can shift in and out of 5th gear without issue. Smooth, firm, fast shift, or at leas no more inconsistent than the other gears. So I'm assuming that the transmission fluid must be low (it's an auto, with a GM box). I've found a few conflicting reports on how to check it, some saying the car must be on, others that it should be off. Some say if you loosen the fill plug, fluid should dribble out, others say to stick a finger and wiggle to try to feel for fluid (That makes me a bit nervous :p). I guess the question I have is if anyone has any input on if this is really a trans issue, or a wild card somewhere else (i.e. pre-cat O2 sensors?) and also if anyone has an official, or proper way to check the transmission fluid.
Thanks for the help!:thumbup:
You may not have looked deep enough as there should be no "conflicting reports". There's only one way to check it - engine running, in Park, after running through the gears a few times.

The "official" way has been posted before. Just search man. They're everywhere on the net - YouTube, Bimmerforums, Bimmerfest, E46F and even a few blogs here and there.
 

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Discussion Starter #3
my biggest question was what exactly should i look for. I watched a few youtube videos and looked at a couple threads, and some people say it ought to dribble out, while others say to fish around and try to feel for the fluid. I guess that's what I'm most questioning here... But thanks for the heads up!
 

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You may not have looked deep enough as there should be no "conflicting reports". There's only one way to check it - engine running, in Park, after running through the gears a few times.

The "official" way has been posted before. Just search man. They're everywhere on the net - YouTube, Bimmerforums, Bimmerfest, E46F and even a few blogs here and there.
+1

Also it needs to be warm and level. It should just drip out a little. None coming out at all means you're a little low at least. I doubt you are low on fluid though. Either your fluid is in bad shape and you need to change it, or you've got a bad sensor, or a slipping clutch pack.

That code indicates slippage assuming the speed sensors are good.
 

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my biggest question was what exactly should i look for. I watched a few youtube videos and looked at a couple threads, and some people say it ought to dribble out, while others say to fish around and try to feel for the fluid. I guess that's what I'm most questioning here... But thanks for the heads up!
Whether you fish for it inside or let it have a small stream will be a couple mm difference and won't matter. You'll probably have bigger variances depending on how you level the vehicle.

That said the correct procedure is a small stream, not gushing out, while the engine is running. If you have to reach inside to feel for fluid, it's low.
 

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Discussion Starter #6
ok thanks gents
I'm going to have to assume that the clutch packs are slipping then. I'll check the fluid and hope for the best, and then i'll go from there. Sorry if the post was a little redundant, and I appreciate the input.
 

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Im had the same problem after i had to change the oil cooler and had to refill the trans whit new oil,
But on my case i did the refill and did not have the car level , make sure the car is level when you do it.
It should have a small stream coming out like CVX5832 said
 

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Discussion Starter #9
nope, no clunking. I admittedly drive pretty hard, and 90% of the time in manual mode, so I do my fair share of down shifting. The transmission makes no noise upon shifting in either direction, either up or down. It feels reasonably smooth to me, I know it needs a fluid/filter change (85k miles), but the car just came under my ownership (less than 2k miles) and I haven't quite gotten around to it yet. It always goes into limp mode when holding gear, I haven't had it go in during a shift.
 

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Discussion Starter #10
and also, thanks for the tip about filling level gr-racing!
 

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Vehicle as level as possible, partially warmed up transmission fluid.

You may want to crack the fill plug loose while the engine is off, but do not fully remove the fill plug at this point. Fill plug should only be removed and installed with the engine running.

Trans fluid should not be "hot", more an issue about burning and scalding than anything, trans fluid usually runs close to 200+F fully warmed up. You want the trans fluid between 100-120F as I recall, you should be able to keep your palm on the trans pan for a few seconds without getting too hot and not to burn youself. Temp is not really all that critical as long as it is not too hot to burn your hand.

DO NOT PUT FINGERS INSIDE A HOLE WITH ANYTHING RUNNING IF YOU WANT TO KEEP THE TIP OF YOUR FINGER. No need to do this.

Trans fluid should just stream out in a very small stream, just faster than a drip.

As mentioned, there should really be no confusion about checking the auto trans level. Manual trans and differentials are checks with the car off, not parts moving, automatic ALWAYS with engine running.
 

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Discussion Starter #12
Thanks!
As a medical student, I try to be careful with the whole popping my fingers in running automobiles... could be surgeon's fingers, y'know?
But thanks guys. Anyone with further ideas about my issue, please chime in!
 

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While you're under the car, check the connection at the main electrical connector to the transmission. I believe it's a large, round connector with a number of pins.
 
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