2009 g37 sedan auto won’t start and dash will not display anything but press brake and blank when on, fans do come on.

 

As i stated in your other thread, the issue is likely either the IPDM/er or the ECM. Whenever the fans come as soon you turn the key ON indicates that the ECU has lost CANBUS communications:



Again, any chance the ECM or anything got wet?

This might have nothing to do at all with the engine swap.

 

The coolant connector busted while driving, water went everywhere.

 

How can I troubleshoot the ECU ?

 

I am going to tag @BULL here as he may have some ideas. I do not think it is the ECM but rather the IPDM/er. Any chance it got wet from coolant when the heater hose connector failed?