Aux out switching to gnd when ecu powers down

[randolph]

Hello guys,

having a little issue with an oem wiring vehicle fitted with a g4x fury whereby the fan turns on when ignition is off, Before i go fix this in any other way i just want to know if all of the aux out on the g4x switches to ground when the ecu is powered off or is there specific aux(s) that completely disconnects the circuit when off.

thanks

[Adamw]

The aux doesnt switch to ground, what is happening is when you switch off the power supply to the ecu, because your fan relay is still live, this 12V then feeds back through the flywheeling diode onto the 12V rail, trying to power up the ecu and everything connected to it.  

If you have a spare ignition or injector drive then you can move the fan relay to one of these as they dont have flywheeling diodes.  

 

[randolph]

Adam,

the fan is on ign6 already.

using a test light with ign 6 aux to one side and the other to batt+ the test light turns on when i switch the car off.

 

[Adamw]

We use Ign drives in many of our plug-in ecu's for hot-fed fan relays without issue.  There is no back feed path to ground or to 12V through an ign drive when the ecu is off, it will be open collector.  

[randolph]

4 hours ago, Adamw said:

We use Ign drives in many of our plug-in ecu's for hot-fed fan relays without issue.  There is no back feed path to ground or to 12V through an ign drive when the ecu is off, it will be open collector.  

next time i have the car i will triple check everything again, but just to note that the wiring on this car is still in oem form without any mods to it(rx8) , the fury is being used to control everything except the canbus which is being control by the oem one.