This post is a bit of an introduction as well as a cry for help...

So my son just got his first car, a 2005 Grand Prix GT1. 140k miles, fairly decent shape inside and out. No rust, and it runs/drives great. Also, it's Bermuda Blue.

The problem with this car is that it sat under a carport for 2 years extremely neglected and untouched. Blew off the dirt, inflated the tires and charged the battery, it made the drive across town to my house just fine. Got into the driveway and the Check Engine Light came on.

When I plug in my OBD2 reader, the power light comes on, but it will not communicate with the car. I've tried using a generic ELM327 Bluetooth reader, as well as my VW/Audi VCDS cable (which *should* also work as a generic code reader), with the same results for both.

When I look under the dash, there's 4 wires coming out of the OBD2 port, appear to be wrapped in the factory electrical tape until it goes up under the dash. Not much to see, hard to see if there's any issue there.

Under the hood is a different story. A rodent of some sort used the engine bay as its living space for quite some time. There's nests under the engine cover and inside the airbox, and turds all over the place. So I've disassembled the airbox, all 3 connectors to the ECU look just fine, and I peeled back a bit of the factory wire loom to inspect the wires going into the airbox for the ECU, and didn't see any damage.

Additionally, neither fob will work to lock/unlock the car, however the trunk and panic buttons work. The remote start button will cause the lights to flash, but will not start the engine. I understand this is likely because the CEL is on, but I'm wondering if the other fob issues are related here.

Has anyone encountered similar issues? Am I about to go down a terrible rabbit hole of chasing wires looking for damage deep in the harness? Or are there specific connectors I should be looking for that are a known issue?

Thanks in advance for any help!