Want to "Fix" your SMG? Look Here!

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.

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

Awesome write up and discovery of the decade Now I have to get used to the SMG light not coming on, lol.

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....

Interesting stuff.

Now the question remains: to preventative mod or to corrective mod.

Originally Posted by grantmax

Interesting stuff.

Now the question remains: to preventative mod or to corrective mod.

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 .

Originally Posted by grantmax

Interesting stuff.

Now the question remains: to preventative mod or to corrective mod.

Personally, I wouldnt mod anything unless i had a problem with it.

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

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.

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=aznniche;13522220]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?

Originally Posted by jimmyboy72

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

Have you done the mod as of yet? Summers almost over...lol

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.

Originally Posted by 02carbonM3

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.

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.

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

i wish i was good enough with electronics to do this.

after my install, i haven't had the SMG/SES light come on yet, although I haven't driven in stop and go traffic where my car would creep along.. will continue to test..

Originally Posted by 02carbonM3

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

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.

Originally Posted by 03DinanS2

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.

i would like to get one of these resistors myself to try on my car. my car turns the cog light and pops me out of gear whenever it gets hot in stop and go traffic. its been hot and humid here in socal the last few days and its been happening a lot on my commute. I'm constantly worried that ill get rear ended if it happens while driving. my car has 160k miles now and i unfortunately put a salvage title on it so financially it doesn't make sense to spend so much on a new pump

Pm'ed!

Originally Posted by 02carbonM3

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

Be sure it's the solid white wire. It can get a little dirty and dusty under there, I had to wipe the wires down to be sure I was splicing into the correct one. Be sure your connections are solid and well protected with electrical tape so the elements from foul weather such as rain doesn't penetrate and short out anything. Any doubts or concerns, contact 03DinanS2, he'll put you on the right path

Originally Posted by rcsummers

i wish i was good enough with electronics to do this.

this mod is so simple that it's almost unbelievable given the problem it fixes. If you have never spliced and crimped wires with butt connectors before, hit up YouTube to get a visual of it. There's only one wire you're going to cut and insert the resistor inbetween. It really is cake .

Originally Posted by msane3

i would like to get one of these resistors myself to try on my car. my car turns the cog light and pops me out of gear whenever it gets hot in stop and go traffic. its been hot and humid here in socal the last few days and its been happening a lot on my commute. I'm constantly worried that ill get rear ended if it happens while driving. my car has 160k miles now and i unfortunately put a salvage title on it so financially it doesn't make sense to spend so much on a new pump

Well, luckily for you and the guys in Texas that you all have a Fry's electronics store. Up here in the NE we only have RadioShack which fell off bigtime . Their ceramic encased resistors weren't the correct ohm's. If Fry's doesn't have it in stock, try Orvac in Fullerton. I think a lot of the M3 SMG guys have hitting up Fry's depleting their stock, lol.

This resistor mod is definitely the fix of the decade! Big props to 03DinanS2