So I'm trying to help my friend with his Civic. It went into limp mode when he downshifted one day. We have done the following:

Checked timing, it is perfectly in time. Crank keyway is straight up when the "UP" is straight up on the cam gear.
Compression test, average of 180 with less than 5% difference across all cylinders
Replaced camshaft position sensor, crankshaft position sensor
He was having issues with oil leaks, so they were coated in oil, hence replacement of the sensors...
Air filter isn't clogged, cat isn't clogged
OBD2 scanner won't connect to read codes
Tachometer only works for maybe a second upon initial start-up
Coolant temp gauge doesn't show any reading
Green key light is flashing constantly
Won't rev over probably 3k rpm

He has a kid that likes to suck on his keys, she's like a year old... would the drool cause his key to lose the immobilizer programming? The civic drives perfectly fine, just hits the rev limiter way before it should.

 

Do not use the crank keyway for timing checks. If you can't see the mark on the crank timing gear (because the lower cover is still in place), probe in the cylinder to feel the top of the piston and confirm TDC of the crank.

Yes, immobilizer system is active, take car to dealer and have them set up a new key, then find kid something less expensive to chew on.

 

So we took the car to the dealership here and they said they couldn't read any codes or communicate through the OBD2 port. They said the issue is the ECU and it would need to be replaced. They told us specifically that you cannot use a used ECU, you can't reflash it, it won't work. I nodded and left.

I called the dealership that is one town over and they said it would cost $65 to reflash a used ECU, just make sure it is the same part number. They laughed when I told them what the other dealership said...

Is it safe to drive this car in limp mode to another town? It is about 45 minutes away.

 

Go to Autozone or some auto parts store that will let you use a code scanner. Hook it up and see if you can communicate with the OBDII port. If so, go get a new key made first and test that before putting in another ECU. I wouldn't trust ANYTHING the first dealer told you.