Codes P2127, P0651n and P0452?

Hello, does the vehicle run and drive, or are you having issues there too? And what made the thump you described, was that driving or when you started the vehicle?

These codes are pointing to one of the 5-volt Reference circuits, the 5v Ref is used for sensor signals, its outputted by the PCM by a voltage regulator internal to the PCM, and when a 5v Ref either gets shorted out due to a bad sensor or it gets shorted to ground, whatever other sensors that use the reference will set codes as well, hence the APP code and the P0452 (Fuel Tank Pressure Sensor Circuit low voltage code.

Do you have a multimeter to check for voltage at the APP sensor? It's a very easy check to do. Just Key On, engine off and we'll have you check the two 5volt References that the APP uses
Also does your A/C work? Just asking because it looks like the AC pressure transducer uses the same 5volts as the Fuel Tank pressure sensor.
Here is the OEM wiring diagram to check the APP sensor harness connector. If you were driving when you felt the thump, you may have hit something and damaged the Fuel Tank pressure sensor which is back near the fuel tank, and it's the area causing the fault. But to quickly verify there is a low reference voltage the APP sensor is much faster to get to.

If you find that the voltage at the APP sensor is incorrect while unplugged, and the fault on the 5v Ref was caused by another sensor being shorted out, I would put the old APP sensor back in if it's an aftermarket part, if you got it from Honda and it's an OEM part then you're okay. It's just better to have the original equipment in there when possible. Especially when it comes to sensors, a lot of aftermarket parts now are junk.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

The Fuel tank pressure sensor is attached the Charcoal canister which is also part of the Evap system, both are back under the vehicle near the gas tank, and because the Fuel tank pressure sensor and the APP sensor share a 5volt reference, if the fuel tank pressure sensor was damaged, by backing into something, and it shorted out, it will cause the 5 volt reference to drop below 5 volts, hence effecting the APP sensor as well. I don't know about the ballast, it depends on how it's wired. The first thing to check is the condition of the Charcoal canister and any wiring to it.
Have you gone through and checked all the fuses as well?
We can only go by the information you give us, if there's no 5volt ref to the APP sensor there will be no throttle signal to the PCM. Thats why you need to check if it has both of them, that code is for the APP B sensor, so there is probably only one of the reference voltages missing. It's just how those 2 sensors can set codes and together. If the APP sensor only has 5 volts on 1 of the 6 wires, you need to figure out why. There are other sensors on the vehicle that share other 5v Refs as well. The codes you're getting are for the B Reference voltage., Go through and check every fuse in the vehicle as well. There's a fuse panel in the engine compartment and another under the dash.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

These are circuit codes; you need to check and see what the voltage level is for Reference B. The code P0651 is the PCM detecting the malfunction internally, so you may unplug one of the sensors and the 5volts might come back. This is why you have to use a multimeter and check; it's just easiest to check the APP sensor because it's easy to get to and unplug. If the Grey wire is missing 5volts, unplug the throttle body and recheck the grey wire.
Faults occur in vehicles like this all the time, when it comes to electronics, anything can happen at any time. I'm surprised the vehicle even starts.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Okay, glad you got it fixed up; did they give you the old PCM back? I try to repair them on the side. Kind of a hobby you could say, but if I can repair it, you'll have a spare PCM. Did they say why it went bad? I'd think for a 2014 there would have to be a bad ground or something else that caused the PCM to fail a 5v reference circuit, seems odd. Those circuits are internally protected quite a bit, even from shorts to ground, they can bounce right back from that. Let me know if I can be of any help.

Yes, some manufacturers will seal the computers up so no moisture can get in, but I can take them apart without damaging anything. The must have thought the voltage regulator had burned up somehow. Was the ballast you had for the lights an aftermarket component? I'd be interested in seeing what actually happened inside. If you want to leave me your email, I can contact you on the side and you can mail it over, I'll take it apart and see what happens. I'd think that if the ballast was the cause, it would have taken out more than just the PCM. They're suggesting a voltage spike on the ground side probably caused that, but idk. Did you find the ballast with burn marks on it or physically blown open?

You mean the head lights were flickering before all of this happened and then finally some time that night you experienced the fault? The ballast is there to regulate current for high intensity, so if the ballast blew up some capacitors and caused a direct short to ground, it should have popped some fuses, depending on how it was wired into the system. Im still curious though. Leave me your email and Ill contact you with my other email account. I just cant have people emailing me from the site, we need to have traffic directed to the site. It helps us out a lot that way. I will email you tonight or tomorrow with a mailing address you can send the PCM too. It's usually about $10.00 for modules to ship. I don't charge for these repairs, since it helps with future issues like this.

You can email me at MobileTechRh45@myyahoo. Com and I'll get back to you tonight or tomorrow, just let me know the vehicle under the email subject.