So the background. 2011 Sentra 2.0 stock 114,000 miles

This started with just p131 A/F sensor 1 circuit low voltage, and Also occasionally p101 MAF would appear intermittently...
Indeed the voltage was dropping to very low voltages and sometimes 0 upon deceleration particularly letting off the throttle just after fairly high load. I was pretty certain the sensor wasnt the issue, but went ahead and replaced the upstream A/F sensor due to mileage. Still p131. Found the assumed air leak, the lousy ribbed intake tubing just after the MAF was torn and cracked, replacing it has taken care of p131, check engine light off. Still
In this time I noticed the air intake temp sensor is always reading about 10°F-15°F above the outside temp and the coolant temp on stone cold engine (average outside right now is 50-60°F and sensor always reading 75s).
So, replaced air intake manifold gasket, throttle body gasket, cleaned throttle body plates, cleaned MAF with MAF cleaner, replaced spark plugs, as well as rocker cover gasket (valve cover gasket) no avail. I then very very carefully took the MAF sensor out still attached to harness to test outside air temp, thinking maybe the air intake tubing is warmer inside. That instantly threw p113 intake air temp sensor 1 circuit high and p101 MAF performance and the intake temp read 93°F in that moment (faulty wiring?) I put the sensor back and it went back to reading 75s, it was about 56°F outside.

Then I tested MAF sensor harness for IAT and MAF power supply, both had solid voltage supply. Then I tested for continuity for both sensors output to the ECM. No continuity. It is possible I didn't probe the ECM harness properly or well enough. I used a saftey pin. Scan data has always reported the sensor data for both MAF and IAT, so I'm doubting there is no continuity there??

At this point, forgetting only 1 ECM harness was plugged in, I turned the ignition on for 2 seconds until I realized the radiator fans kicked on instantly. Now I have p130 and p1148 check light, and permanent stored codes are 101, 113, 1148, and 130, and ECM is stuck in open loop, the fuel system PID reads open loop fault about once every min for about 5-10 seconds, and A/F (new sensor) voltage stays locked at 2.2V and equivalence ratio stays locked at about 1.06.

I greatly appreciate any input at all. My main question is did I damage my ECM? How can I test the ECM to know if it's good? And did i read no ECM continuity on the MAF IAT sensor output because improper probing? I know I should of probbed from the rear of harness instead.

Later tonight I will swap the old but still good o2 (A/F) sensor back in to see if i fried the new sensor. Thanks guys

The harness that was left plugged in was the bottom most F24 grey harness.

Maybe you torched it and maybe you didn't. Only the designers know for sure if part of harness plugged in and part not fries things. Should never do it to begin with. Need to plug all back together and then leave battery disconnected to see if codes wipe when it gets connected back up. Obviously you will get codes for everything left powered down by being unplugged.

Only way to check the ECM is to switch with a known good one, dealerships cannot even fully test ECMs and what they do. Chipkeys matched to ECM have only made that worse.

One of the biggest issues with checking parts with the tiny pins they use now is getting into the connector without damaging it, anything big enough to connect can slightly open the connection up to not touch the pins when it goes back together.

Pretty hard to fry an O2, the main power comes from the unit itself and any supplied by the ECM is just for the heater section of it.

Thank you for the response i appreciate it. Turns out the A/F sensor harness unplugged, it will not snap closed and lock.

Probing ECM harness is absolutely necessary in diagnosing many times. The proper way is to probe at the rear of the harness, for every pin there is an extra slot for probing. Cleared codes with proprietary scan tool. Shouldn't return, until harness disconnects again or intermittent MAF fault returns.

As for the ECM programming, it requires nissans Consult-III 'scan tool' software, I would hope a dealership better have the consult if they're working on Nissans lol, but to put another ECM in requires that programming I believe. The Consult-III does everything from programming keys to engine trans airbag everything.