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Want to "Fix" your SMG? Look Here!

132K views 106 replies 55 participants last post by  dtebh916 
#1 · (Edited)
There are many many issues that can arise with the SMG/SMGII. This thread is aimed at one specific, common issue that leaves many SMG owners timid to drive on hot days.

Here are the symptoms:

On hot days with little air flow through the engine bay IE traffic situations, the SMG and SES light illuminate and soon after, the gears drop out into 0 or nuetral. Very dangerous situation at times and for many is guaranteed to happen daily while others only happens a couple times a year.

I have found the cause of this to be a horrible design flaw of the SMG HYD Pump temp sensor being mounted way too close to the engine. As a result, while you are sitting in traffic (with no airflow to cool it off it gets hotter and hotter) the HYD Pump temp sensor picks up heat from the engine and sends a signal to the ECU telling it the HYD fluid is "too hot." This is not the actual case. The result is the circuit that tells your pump to charge the accumulator is momentarilly disabled. You have two or 3 shifts left in the accumulator and after that there is not enough pressure to make the next gear so it drops to nuetral. after about 15-30 seconds the circuit is momentarilly restored and the accumulator charges again...the cycle repeats over and over again untill you can get on the highway or just simply shut the car off and let it cool for at least half an hour.

To stop this problem from happening i experimented and read through schematics for 3 days and what i came up with worked for me and it also worked for another member of this forum whom i was sharing ideas with. The best part is it it costs about 5 bucks if you do it yourself.

Take a 500-1K ohm heat resistant resistor and splice it in series with the temp sensor. its that simple. it takes about 20 Minutes start to finish. i waited about a week to post this to make absolutly sure the problem was gone. you can access the connector that goes from the ECU to the HYD pump from unterneath the car just "inboard" of the front driver side tire. there are 18 wires on it i think and all sorts of colors. the wire you want is the SOLID WHITE WIRE. Just cut it, splice in the resistor and wrap it up tight and your done.

Now keep in mind that this does not keep your car from heating up the actual sensor but instead, adds a temp "bias" for your ECU to not allow it to reach the over temp voltage. This in my opinion is safe, effective and a dream come true for the price. Remember, the only possible effect of hyd fluid over heating is premature wear of the pump itself...chances are if you have this problem, you were told you need to replace the pump by the mechanics for about $3500...Sounds like we have nothing to lose right? Especially since the hyd fluid isnt really overheating in the first place and its just the engine heating up the sensor that is aprox 3/4'' away from it.

Below are some pics of the procedure as i did them on my M. Enjoy. And have a great summer this year without fear of having your Bimmer look like a turd on the side of the road or blocking traffic.:pimpin:

EDIT:
CNTRVSY's Thread on M3F: http://www.m3forum.net/m3forum/showthread.php?t=372262
 

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#3 ·
Great contribution, I've owned two SMG Ms, one was a VERY hard driven track car, never had this issue but see it on the forums, it will be interesting to read the replies here to see how prevalent this really is, we get several 100 degree days here, never an issue....My only heat issue is a tendency for the NAV screen to lose scroll lock after several hours of top-down driving in really hot sunny conditions. Replaced the unit once, still does the same thing, but maybe 1-2 times a year....
 
#5 ·
It's a bit of both, if I'm reading your question correctly. Corrective in that hcu temp fails prematurely due to it's poor location causing the system to think it's overheating and Preventative in that it prevents you from spending big $ on a new pump that you may not actually need :).
 
#7 ·
AWESOME NEWS!!!
I have been driving my 04 M3 like "Grandma" since March. I live in the Phoenix area and have made several trips from here always North to cooler weather. I can tell you that once I leave the valley of the sun, the engine cools down and runs fine. I have found that running my AC, sport settings maxed out and driving hard causes my SMG to fail and has happened twice now. BMW has told me they will replace it for $5,500 not including labor. I have always suspected what you have discovered. I'm in the process of studying to become an electrical engineer. So far this car in the last 18 months has ran up a tab of over $5,500 in repairs. Not very happy about that, but I love this car. I will post another note on here after the repair and let you know how it is handling. Here should be a great testing grounds for this repair; as the heat here has been reaches 115 degrees. Thank you once again!
James
 
#8 · (Edited)
I have recieved numerous PM's regarding how my ///M is doing since i performed this mod so ill just post on here with results:

4K miles later in the middle of the hottest summer ever, absolutly ZERO issues of my SMG falling out of gear. Temps read on the dash of around 110 every day here in fl and i have been in traffic with heat like that every single day. Not one issue. One might think this is too godd to be true. Well its absolutly true and will work for you too. Its simple electricity. I dont even think about it anymore when before i was scared to drive through the city bc it was GUARANTEED to happen every day.

Anyone who has done this mod besides myself please post here and let us know of your success.
 
#9 ·
I have the same exact issue this past weekend and hope BMW would come out and perform a recall for this HCU Temp Sensor. I bought a 3.3K Ohm resistor as mentioned on another thread and will try it this weekend. I've been waiting for my SMG/SES lights to come on, but they have not yet. Maybe this is due to I'm not driving in stop and go traffic, but I sure am not confident in driving my car.
 
#10 ·
I have the same exact issue this past weekend and hope BMW would come out and perform a recall for this HCU Temp Sensor. I bought a 3.3K Ohm resistor as mentioned on another thread and will try it this weekend. I've been waiting for my SMG/SES lights to come on, but they have not yet. Maybe this is due to I'm not driving in stop and go traffic, but I sure am not confident in driving my car.[/QUOTE

BUMP! How We Doing?
 
#12 ·
I just tried this.... Installed a 3.3K risitor from radio shack! My car went nuts after about 10 min of driving. The smg light came on and the ideal was reving up to 3k and down. If I hit the gas the rpm would drop like it was cutting out. Removed the resistor and all back to normal.
I had replaced the trans temp sensor at the same time so I'm hoping that that was the issue. Replaced the relay and pump sensor las month but the light would come on after an hour of driving and drop out of gear.

I'm not sure if I purchased the right resistor. It was a 3.3k 1/2 watt...... It was really small not like the ceramic one.
 
#13 ·
Well, here ya go. For one you used a resistor that is not heat resistant. The type you used is for small circuit board electronics. "My car went nuts after about 10 min of driving." I dont doubt that seeing as how after 10 minutes it would be so hot by that resistor you put in who knows what signals the ECU was recieving. Second, even so with the wrong resistor being installed i dont see it causing a problem with your idle. You need to make sure you "tapped" into the correct wire. It sounds like you missed the mark my friend. The important thing is that you put things back to the way they were and your car is running fine now. There is another forum on M3F about this mod and noone has had this problem. Shoot me a PM and we can go over the procedure in more detail and i can send you a resistor in the mail. i still have a couple. Good luck bro.
 
#14 ·
Thanks for the reply! I thought I did the install correct. You mentioned the white wire and I'm guessing the resistor I used screwed everything up. I still would like to install the correct resistor! Where did you purchase yours and what are the specs. As you mentioned, If your willing to part with one of yours I can text or email my address. Thanks again
 
#17 ·
PM me your address. Ill mail you one out. You cant typically buy the kind i used. They are US Military spec. I know how desperate this feels. i had my ///M less than 24 hours before this happend to me and i was thinking i got totally screwed. Stayed up till 2 or 3am for a few days till this popped up and seemed like a good idea. Theres dozens of threads on this subject that served as viable research and when it actually worked, It was like i was on top of the world. Ill post the link to "cntrvrsy's" forum tas per an EDIT in the OP. It has better pics than the ones i took. The mod worked on his M as well. In one of the DIY's it says you have to remove a panel on the bottom. You dont. You can get to it from inside drivers wheel area.
 
#21 ·
Is there any way you can do a full DIY write up of this (to include detailed pics for us electronic illiterate people) and tell us where we can get the parts from for this (including part numbers)? Would really appreciate... Thanks for the info so far!:hi::thumbsup:
 
#24 ·
There are many many issues that can arise with the SMG/SMGII. This thread is aimed at one specific, common issue that leaves many SMG owners timid to drive on hot days.

Here are the symptoms:

On hot days with little air flow through the engine bay IE traffic situations, the SMG and SES light illuminate and soon after, the gears drop out into 0 or nuetral. Very dangerous situation at times and for many is guaranteed to happen daily while others only happens a couple times a year.


EDIT:
CNTRVSY's Thread on M3F: http://www.m3forum.net/m3forum/showthread.php?t=372262
Hello All...

I have a '04 M3 with a SMGII.
Bought with 90K on it and runs great!
Take it to the track quite often and run the snot out of it!

I had this over heating issue as described. (never on the track though..)
When it happened to me it was 92 degrees outside and got stuck in stop and no go traffic. My SMG warning cog came on, but all was still running normally. Once cooled down I was not sweating it as much on a mountain pass. Also, the service engine soon light was on (normal with SMG failures) I pulled off to take a break for 10 minutes. All was Normal, no warning lights. Had a feeling it was a temp sensor causing the failure, and guess I was right by reading this thread! I will have to try the 500 to 1,000 OHM resistor trick. Have many laying around. (not 3,300 or 3.3K OHM) as in another reply to this thread.

Here is my additional SMGII problem nobody seems to know about how to solve.
Cold or intermittent problems.
On 2 occasions now when cold I got the SMG cog. I had to turn off, wait 5 seconds or so and try again. I have had to do this several times!
You MUST turn OFF the ignition and WAIT 5 seconds or more after the dashboard goes dead before attempting to start the engine. Really sucks when you successfully back up, then you can't shift to first gear! Have to sit there and turn off the engine and reset the computer to see if it will now engage in gear.
I do have to take my shoes off to count how many SMG failures I have had in the past 3 months! The mechanical side of everything is just fine! Damn computers!

Any ideas on what the problem is?
I am thinking electrical issue or sensor going bad.
Maybe the Salmon colored relay??
Need to get the fault codes to see what the computer says it is, but I have no reader for this.

Thanks in advance...

Scott
Salinas, Ca.
'04 E46 M3 Carbon Black SMGII
 
#31 ·
Scott,

Sounds like your accumulator sometimes doesn’t charge. The salmon relay i the "link" for that engagement. I'd try that definitely. Especially if it intermittent. That how relays typically fail. Also, make sure your car had the relay bulletin done by BMW.
 
#25 ·
^^ What does the gear indicator display show when your car is acting up where you have to shut it off for 5 mins? Example, when you back the car up and try to select 1st gear, does the display show 1st or is it still in R? I would try the salmon colored relay first and see if that fixes the gear change issue. If it doesn't, then you'll have to try and find a shop or local member that can read out the SMG codes for you.
 
#37 ·
in an effort to thank the e46 fanatics community (and because I was gonna have to pay $10 to ship these $1 items) I bought several of these. PM me and I will simply send you one. Free. No strings. If this fixes my m3 it will be the first time I have been able to fix any issues on this car for less than $300. So hit me up, I got 10 to give.
Kevin
910 Ohm 10W Resistor Wire Wound 5% Tolerance
Part Number: 016-910
 
#38 ·
All of this "good news" is prompting me closer and closer to buying that car I've got my eye on...its absolutely beautiful but I'm hyper-sensitive right now about dumping the $22k to bring it home due to all the issue with SMG...is $22k a fair price for an '05 w/ 71k miles, SMG or should I price seller down??
 
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