battery disconnect switch + ECU power

[Goblinfanclub1234]

Hello

I have a battery disconnect switch and when I turn it off I am cutting power to everything including the BCM and ECU. I don't want to keep resetting my ECU every time I use the switch.

Does anyone know how I can keep constant power to the ECU so it remembers everything its learned while still cutting power to the rest of the car?

Thanks!!

 

[Gtstorey]

Run a fused wire from the battery to which ever pins have non switched power to them. Or have a second battery with an isolator between the two

 

[Goblinfanclub1234]

thanks! I am trying to determine what needs constant power for my LNF

another side effect of this battery disconnect is that my odometer is still at 0 since finishing the build.

 

[Gtstorey]

What’s the purpose of the battery disconnect? If it’s to keep the battery from draining while sitting, leaving the ECM and bcm connected is the main parasitic draw while sitting.

Battery disconnect shouldn’t have anything to do with odometer reading 0.

if you are looking for which pins need battery voltage, there has been a link to free online service manuals posted several times recently. You can either connect at the pins or trace the diagrams and try and tie in at the fuse box.

 

[Chubbs]

I have a remote battery disconnect on mine, which is both an anti-theft measure and a battery drain solution. My recommendation is....don't use a battery disconnect. Use a trickle charger instead.

Since using the battery disconnect, i've had a wide range of odd electrical gremlins. Sometimes the car refuses to start for the first 5 minutes or so after restoring power. Sometimes the gauges don't work. Sometimes the gauges are intermittent for half an hour or so, then work fine. Sometimes it will reset the oil change interval and trip odometers, and sometimes it doesn't. All of these problems go away if I just leave power on the whole time, and hook up a trickle charger.

I understand leaving power to the ECM/BCM would probably fix those issues, which is what you want to do. But that also mostly defeats the purpose of a disconnect in the first place.

 

[Goblinfanclub1234]

I have a remote battery disconnect on mine, which is both an anti-theft measure and a battery drain solution. My recommendation is....don't use a battery disconnect. Use a trickle charger instead.

Since using the battery disconnect, i've had a wide range of odd electrical gremlins. Sometimes the car refuses to start for the first 5 minutes or so after restoring power. Sometimes the gauges don't work. Sometimes the gauges are intermittent for half an hour or so, then work fine. Sometimes it will reset the oil change interval and trip odometers, and sometimes it doesn't. All of these problems go away if I just leave power on the whole time, and hook up a trickle charger.

I understand leaving power to the ECM/BCM would probably fix those issues, which is what you want to do. But that also mostly defeats the purpose of a disconnect in the first place.

I do have a trickle charger and I am going to take your suggestion and remove the disconnect I think

 

[Ross]

Some racing associations want a battery cut off switch too. I'm guessing it is for fire or arcing termination.

 

[Desert Sasqwatch]

A small lithium 12V battery tied into the hot key-off circuit with the proper connection into the alternator charging circuit but backflow protected (blocking diode), that is separate from the switched main battery cutout wiring, could be used to keep the ECM and BCM alive. Not certain how well it would play with LAN system, if there would be any affect all, but it could be an option.

BTW, on the later model '08-'10 donors, I've read that some battery drain problems may be the result of the BCM not seeing the driver's door switch cycling and keeping some circuits active. The solution has been a momentary switch to open this circuit to fool the system and is reported to have been an improvement.