Removing SMG Auto Prime Function

[Darbshaw]

Hi guys,

I have my SMG that is a track car only and I have a smaller lightweight battery. It’s the 11lb braille battery, I don’t remember the model number. I want to remove the priming function to save the battery from draining.


Is it possible to decode the auto prime function for the SMG pump on everything but the key being in position 2?

I know there’s a way to remove it from the door switches mechanically. My driver door switch is broken so it reads as always closed. So the pump won’t prime from the driver side opening. Downside here is that my window doesn’t auto roll down with it. So I’d like to not go this route for the passenger door if it’s avoidable.

Eventually I’ll move to poly windows in the driver doors and this won’t be an issue. I’d rather not do that for the time being though.

Thanks for any help, I hope I got the question across clearly.

[George Hill]

This is an interesting idea. I highly doubt there is a coding option for this as I think BMW sees it as kind of a "safety" feature ensuring the SMG pump is always ready to start.

If you don't make any headway on the coding, then you could potentially install a switch between the Salmon relay and SMG module that would prevent it from grounding the relay coil. I'm not sure if this would make the SMG unhappy as its trying to run the pump without pressure build up, but something to consider

[Darbshaw]

This is an interesting idea. I highly doubt there is a coding option for this as I think BMW sees it as kind of a "safety" feature ensuring the SMG pump is always ready to start.

If you don't make any headway on the coding, then you could potentially install a switch between the Salmon relay and SMG module that would prevent it from grounding the relay coil. I'm not sure if this would make the SMG unhappy as its trying to run the pump without pressure build up, but something to consider

George thanks for the idea! I like this, and will most likely be option 2.

I am certain the SMG unit would throw a fit with this, but potentially since the car would be off while the “issue” is occurring will stop it from throwing any false codes.

My only other thought was to wire a kill switch into the car. Although this falls more into the mechanical intervention than coding. Also I'm not really at the point in this build of adding one in yet. Or in the current budget.


Unfortunately my experience on the coding side is novice at its absolute best. Something that came to mind is that if there is a difference in the body controls modules from a manual to smg car. Then just trying to find a way to trick the body controls into thinking it's in a manual.
Although I would assume this is just an extra signal sent by the smg computer independently.

[George Hill]

I know there’s a way to remove it from the door switches mechanically. My driver door switch is broken so it reads as always closed. So the pump won’t prime from the driver side opening. Downside here is that my window doesn’t auto roll down with it. So I’d like to not go this route for the passenger door if it’s avoidable.

My understanding is that when you open the door, the car "wakes up." The GM sends a signal to all the modules to "get ready." The SMG sees this and then does its pre flight checks and when it sees the pressure is low it primes the pump, just like how the DME primes the fuel pump when you key on. The SMG has to have pressure (shift gears, 1 to N, etc) in order to crank. If the DME had to wait for the SMG to prime before cranking that could be an issue at least on a street car. So I don't think there is any way around it. If have my laptop out today I'll try to look through NCS and see if there is an option, but again I would be shocked if there was.

A kill switch is likely a good solution too. Or maybe just a kill switch for the SMG module itself. But then you might get communication faults while its off too.

Can you tell us more about your drivers door latch quoted above? If the door is always closed it should auto down, there should also be a coding function to allow the window to auto down when open. Auto up maybe an issue if you have the door edge protector removed as you loose the pressure switch.