So proud of myself, found a heat sink, 6 inch fan, got all that installed, took my gem to the beach, 3 miles in… You guessed it. -41 error. I went from 14" rims down to 10", plus the fan and heat sink. I thought I’d have it licked. I have a 2002 e2 with 10.5 hp motor, updated differential gears (done by prior owner). At this point I’m about to drop kick it. So much work, so much customization. My controller was never reprogrammed when I went to the bigger motor. Could that be it? If so, who can do that? Anyone? Thanks for any suggestions.
PS Here’s my little tiffany.
Honestly, I don’t knows what gears. Didn’t do it, was done b4 I got it. Suspect 12:1 but not really sure. Do you know anyone? Marlon was my go-to guy and was going to send me a hand held controller, then he has just been awol forever. I’m just at my wits end. Thanks!
Have thought about going to R4F and getting a new 7.5 motor and getting controller reprogrammed with it. Have made so many mods to this little car, hate to give it up, but I need something I can drive. If I could figure it out, I’d probably convert it to gas at this point! 
(big eye roll)
Hi
Sent you a private message
Hasta,
markos
Just talked to the guys at R-4-F. They say a controller only lasts about 10 years b4 they break down. The thermisters breaking down causes this. That makes sense, seeing how it is happening with less and less miles. My controller is pulled from the car and on the way to them for a rebuild and new programming. 
A $500 controller may or may not fix the problem. I had overheat issues -41 on my R4F motor and a rebuild did stop it from overheating but ever once in a while it poped up
this helps. I’ve installed hear sink & fan and dropped tire size dramatically. They will also properly program for my motor (which they have identified as a blue d&d motor, not the 10.5 as i was originally told, more like a 7.5) my gears 8:1 and my tires. Grant, did you still have large tires? Hoping this is the fix.
Is there a specific heat sink that you would use or just one big enough and drill holes where the controller mounts are?
I bet you have A T-1 controller.
Yes I had a 9:8:1 Transmission
Yes I had large wheels.
I switched to a 10:35 transmission
I switched to a T-2 controller that was rebuilt by FSIP $500 and I still had overheat issues. Sounds like you car has a worn out controller. A Rebuild will make 90% of your overheat issues go away. In fact it may fix it entirely.
I’m guessing your in a hilly Aera. Do a search on this Fourm about -41 and look at controller settings to dial down max amps. This helped with my issues after I bought and installed a new controller
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Actually, I lucked out with a T2 controller. Used to drive my gem to work, yes, slightly hilly. Also had 14" wheels. Now, we winter on an island, with a packed sand road on the beach. So she now has smaller tires. Thank you!
I followed Grant West’s advice and searched fleabay for an old “junk” controller. I think mine came out of an amp. It was about the right size 5.25 x 8. I did not drill anything. Found some wonky furniture type of nuts that screwed on the the existing screws. Hooked springs onto those, then used one ziptie to attach it firmly. Be sure to use thermal grease between it and the controller. I also set up a small fan that is on switched 12 volt to blow on the heat sink whenever the car is on. PM me if you need more info or pics. My car is currently torn up awaiting the controller rebuild.