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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Mon, Jun-26-2017, 04:50:41 PM   #31
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Default Re: New twist on the SMG temp sensor Issue

Seems like this is the most relevant thread so I'll chime in.

Getting codes during the summer when temperatures are hot or when in traffic. Coolant and oil temp are just about in the middle where they should be.

From my understanding, the transmission going into N is a preventative measure to protect it from damage when temperatures are reading high. Apparently pump temperature readings are obtained from the engine, specifically part 13621433076 that is located underneath a coolant pipe on the driver's side of the engine block.

Has replacing this sensor been a fix for anyone? If all the temperature sensors are functioning correctly and it is high temperature causing this, why wasn't this an issue within the first few years of the car being released? The resistor mod tricks the car into thinking temps are lower but people say the issue returns. Would replacing the pump fix something like this if it obtains its temperature values from the engine? It seems over the top as it functions just fine in cooler weather.

Thinking out loud here but trying to understand what's causing these issues and what the fix is.







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Old Mon, Jun-26-2017, 05:39:41 PM   #32
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Default Re: New twist on the SMG temp sensor Issue

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Originally Posted by euro4life View Post
Had mine overheat at the track Monday 3/4 way around the track. Luckily I was able to coast it off the track. Let it cool down and works fine.

Light went off and CEL is gone again. This is the second time it has happened. First time was in stop and go traffic.

There's got to be a decent location to put a tranny cooler on these things.
Move the SMG Pump to the open drug bin on the passenger side. Though the sample size is small, I don't believe anyone has had this issue continue after moving the pump to this location. You might even be able to fit some sort of cooler or fan in this location as well, if you arrange it right. It would be great to route ducting to this location (maybe include an inline fan for when you are sitting in traffic) and have it vent out the fender vent.

Oddly, I had this issue a handful of times last summer in hot temperatures when stuck in traffic for extended periods of time. I only was dropped into neutral twice, the other times only the SMG cog light came on the dash with no change to shifting times or performance. Once temperatures dropped in the fall the issue has not returned to date. I was actually dreading SC summer heat, but thus far it has not been an issue. Keeping my fingers crossed. I have a new accumulator on stand-by and plan to swap the electric motor, temp sensor, and replace the fluid with a higher viscosity fluid, as soon as Vince's (or somebody) comes out with a relocation kit....If the issue returns, I might just piece together the kit myself like others have done.
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Old Mon, Jun-26-2017, 05:49:53 PM   #33
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Default Re: New twist on the SMG temp sensor Issue

There is exceptionally little info of sensors actually being bad, if any. Mostly folks did things around the sensor, usually the "resistor mod", sometimes replacing the sensor.
Ultimately there is *maybe* a handful of cars this has fixed permanently. Not everyone follows up, so I believe the few that may have claimed a 'permanent' fix ... may have eventually failed over time. What this mostly does is moves the "trip point" for the system tripping a failure; this is exactly what the resistor mod does. A new sensor may also adjust this just a hair.
The problem with the HCU is nearly always the DC motor degrading to the point it won't keep up, or eventually failing totally. You can find several threads on rebuilding the motor, replacing it with OEM unit (it's basically an ABS/DCS pump motor on many cars). And there is a 3rd party that has spec'd a new motor (not OE application). I personally don't recommend this, but some of the folks here have done this with good luck - so far.

Relocating the pump after you're having problems is pointless. Once the motor degrades, it can and will only get worse over time. I do expect it helps the longevity of a replacement motor in new condition, or of an hcu still in excellent shape.

As the to failure mode, The car kicks out of gear to protect the driver mostly. That is, if everything goes to hell, you're better off both in motion or stopped with the tranny in neutral, versus stuck in gear, so the unit goes into "failure mode" for safety reasons.

ADS
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Old Mon, Jun-26-2017, 05:55:16 PM   #34
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Default Re: New twist on the SMG temp sensor Issue

We do see this happening across some number of owners, where the system only fails a few times, usually in the hottest combo of ambient temp and drivng conditions (stop and go being the worst). Some folks have gone years this way, maybe indefinitely. It's not a lot of folks, but I've been on here a while and started educating myself deeply on SMG even before I bought my car, as i have a backgound in servos like this, and I can recall reading your situation a few times. Hope it holds up!

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Quote:
Originally Posted by Dr M3an M3 View Post
Oddly, I had this issue a handful of times last summer in hot temperatures when stuck in traffic for extended periods of time. I only was dropped into neutral twice, the other times only the SMG cog light came on the dash with no change to shifting times or performance. Once temperatures dropped in the fall the issue has not returned to date. I was actually dreading SC summer heat, but thus far it has not been an issue. Keeping my fingers crossed. I have a new accumulator on stand-by and plan to swap the electric motor, temp sensor, and replace the fluid with a higher viscosity fluid, as soon as Vince's (or somebody) comes out with a relocation kit....If the issue returns, I might just piece together the kit myself like others have done.
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Old Mon, Jun-26-2017, 07:05:50 PM   #35
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Default Re: New twist on the SMG temp sensor Issue

Red has it about right. I went through about all variants of the SMG heat soak consequences and various temporary solutions, and in the end I found replacing, or properly rebuilding, the SMG hydraulic unit is the realistic solution. Luckily I have a competent BMW shop and a new factory unit replacement. SMG is all working like new for 2-3 years now, not bothered by the heat so far.

There are two phases of the eventual failure. The first part is that the Bosch 387 SMG hydraulic oil temp sensor reports a temperature to the SMG controller that is higher than the actual temp, which leads the controller to switch the SMG into a limp home mode that only gives you certain gears. Eventually the SMG hydraulic pump motor degrades, generating too little pressure, and here too, the controller switches into limp home mode, or when the pressure doesn't come back up, into neutral, along with all the cryptic lights on the dash.

You can change the Bosch temp sensor to a more accurate one, I think from Siemens, but that is only putting off the inevitable replacement of the SMG hydraulic unit.

I might note that the hydraulic pressures are very high and can cause serious injury, so DYI is really only for those who know what they are doing.
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Old Mon, Jun-26-2017, 08:29:53 PM   #36
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Default Re: New twist on the SMG temp sensor Issue

Appreciate the input everyone. Definitely some knowledgeable lads on here

I'd like to extend the life of the SMG unit as long as I can. I feel like a replacement at this stage is premature. When the accumulator or motor starts having issues I'll be replacing the entire unit. Trying to go the OEM route with something like this.

Is there any DIY for the SMG hydraulic oil temperature sensor? It seems like thats where it gets its temperature values and not from the sensors on the engine?
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Old Mon, Jun-26-2017, 09:45:20 PM   #37
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Default Re: New twist on the SMG temp sensor Issue

Do you have the SMG mechanic's training manual?

http://www.leo.nutz.de/docs/bmw/smg_training_manual.pdf
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Old Tue, Jun-27-2017, 04:14:30 AM   #38
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Default Re: New twist on the SMG temp sensor Issue

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Originally Posted by John_T View Post
Do you have the SMG mechanic's training manual?

http://www.leo.nutz.de/docs/bmw/smg_training_manual.pdf
I do now. TY!
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Old Tue, Jun-27-2017, 06:49:48 AM   #39
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Default Re: New twist on the SMG temp sensor Issue

Changed the SMG pump. No issues with heat now. Pumps get old and have to be rebuilt or changed. 110 degrees out and no more issues.
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Old Wed, Jun-28-2017, 09:48:50 PM   #40
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Default Re: New twist on the SMG temp sensor Issue

I just read this whole thread and completely understand the context of the replies now. Looks like I'll be needing a SMG motor in addition to the SMG temperature sensor.
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Discussing New twist on the SMG temp sensor Issue in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)