CEL U0155 and car dying at a slowdown/stop issue?
 

So I'm having an issue with a used '13 FRS I purchased approximately 1.5 months ago. I've been able to register the car 2 weeks ago after having it sit in the driveway for 1 month while the DMV slowly reopened their services. Got my plates in the mail and need to get a state inspection done. I go to a local mechanic shop about 3 miles away for the inspection and failed due to EVAP and O2 monitors not being ready. I was advised by the mechanic to drive 50 or so miles and then bring it back so that the monitors could prep. Went for a 100 mile drive the next day, and brought it back to the same shop for the re-inspection. Before hooking the car up to the live computer, the mechanic wanted to see that the monitors were ready, so he plugged in his OBD2 reader to check the status. He wasn't able to get a reading from the car with the first reader and then tried two other reader and was still pulling up an error message. This is also when I notice that a CEL came on along with ABS and Traction lights came up on the dash. He told me I was out of luck for an inspection and there's nothing he could do for me because he wasn't able to get into the cars system.

I leave annoyed and decided to test my luck at a local AutoZone with their OBD2 reader and sure enough, they were able to pull up the CEL code U0155, which turned out to be "Lost Communication with Instrument Panel Cluster Control Module". Confused and not sure how to address it I head back home to double check with an OBD2 reader I have which reads the same thing. I decided it wasn't much of an issue, cleared the CEL with my OBD2 reader and moved on my with day.

The next day, I drive the car as normal, slowly coming up to a stop sign with clutch depressed and brake pedal engaged, my car suddenly shuts off, similar to as if the car was to stall letting off the clutch. I turn the car back on, proceed to drive as normal and the car shuts off again coming to a rolling stop. Testing the issue out, it happened again a couple blocks out, so I decided to drive back home and disconnect the battery to "reset" the system. I'm assuming the cars computer must've freaked out with all OBD2 readings from the other day. I find that the car's battery negative terminal has a bit of corrosion around it, so I cleaned it off with some water mixed with baking soda. Reconnected the battery and went on a test drive to see if the engine dying issue persists. Was able to test the similar scenarios as to when the issue came about and it seemed the issue was fixed.

Can anyone give insight of why the CEL showed up when the mechanic plugged in his OBD2 readers? Also why the car would end up stalling/dying when the coming to a rolling stop/stop with clutch and brake pedal engaged (also when the car is not in gear, clutch not pressed and brake engaged/not engaged at a slow down/stop)?

Sounds like two unrelated issues. I would start by getting yourself your own reader so that you can be sure of what you have before you go to get tested.

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I'd suggest you get a new battery, that may make the gremlin go away and stay away.