P1065 Description:
Battery voltage is supplied to the Engine Control Module (ECM) even when the ignition switch is turned OFF for the ECM memory function of the DTC memory, the air-fuel ratio feedback compensation value memory, the idle air volume learning value memory, etc.

Possible causes:
Faulty Engine Control Module (ECM) Engine Control Module (ECM) harness power supply circuit is open or shorted Engine Control Module (ECM) harness ground supply circuit is open or shorted

Should i replace the ECM and the harness power supply circuit to to fix this issue and are there any reprogramming procedures i should adhere to?? Thanks in advance!!

 

What years, coupe or sedan, aside from this DTC popping up is the car running NORMALLY?

 

It's an 03 G35 coupe with 170k. The car has actually been running fine for about 2 weeks now since the code showed up. I'm thinking that what might possibly be the issue is that my radio fuse is causing an electric surge of a parasitic amp draw to my battery, even with the ignition turned off. Usually what i'll do immediately after i finish driving i'll take out the fuse or disconnect the negative terminal so that my battery doesn't die.

 

Disconnecting the battery might cause the issue if the ECM recognizes that backup power has been lost before normal power circuit, maybe a capacitor in-line somewhere on the normal circuit that causes it to stay energized for a second or two after backup power is lost and thus the error code. If you have the OEM disc changer it's a known source of parasitic draw, just unplug it if you're not using it.

Pulling fuse 37 in the IPDM will not cause this issue, it powers just AV stuff.

It's also possible the parasitic draw lowering voltage to a certain threshold is triggering the code, clear the codes and see if it comes back with the disc changer disconnected.