Hey guys, I've been researching all over the web to find out what could be causing my G35 coupe to be stuck in its fail-safe mode. I've attempted to diagnose it myself to no avail. The codes it throws are p2122, p2138, p2127, p2123, p1229, p0451, p0453. I've replaced myself both the throttle body and gas pedal. That did not change the problem, in fact, I'm not sure if it is related to the issues but the rpm gauge stopped working and is now stuck past 8000 rpm. Frustrated, I took it to a mechanic shop only to have them replace the same parts I replaced which did absolutely nothing(Worst part is they charged me $80 for diagnostics when they couldn't even figure out the problem causing it). The only obvious problem could be the bad ground(s) behind the radio/Navi and above the ignition cylinder. Others mentioned a bad ECM but when I take a look at the diagnostic procedures or possible causes of the DTC codes, none of them mention a bad ECM.

Thanks in advance for any tips to point me in the right direction. I am moments away from sending it to the dealer because no shop near me does electrical work and atm most of them are packed. My car has been out of commission for more than 2 weeks now and I just want to drive the damn thing.