Hi, this is Bo, an auto expert on RepairPal's Car Genius team!
Yikes, that's quite the cocktail of codes your Camaro is serving up after its winter naps! It sounds like the car's various computers are having a serious disagreement, like a bad conference call where everyone's talking over each other. The U0401 code in your Anti-Lock Brake System means the ABS module is getting data from the main engine computer (ECM/PCM) that it just doesn't trust – like getting a weather report for snow when it's sunny.
When you see a flock of "U" codes like U0121 and U0100 along with it, it often points to a communication breakdown on the car's internal network, or an issue with one of the main modules sending out confusing signals. That "Service Stabilitrak" light popping up during hard acceleration, followed by a brief limp mode, is a classic symptom when the system gets conflicting or out-of-range data from the engine or wheel speed sensors. The P0300 random misfire (especially when warm and driven hard) is also a big player here, as an engine not running smoothly can definitely send data that upsets the Stabilitrak and other systems.
Even with a new battery and trickle charger, long storage can sometimes let little electrical gremlins (like subtle corrosion on connections or grounds) creep in. Given that the dealer has struggled with this before, and since disconnecting the battery isn't the magic bullet it used to be, this likely needs a deep dive. A technician will need to meticulously check the communication network wiring, the main power and ground connections for the ECM and ABS modules, and really pinpoint the cause of that P0300 misfire, as fixing that might clear up some of the confusing data. This isn't just one simple fix, it's more like untangling a knotted string.
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