I have a truck that i replace the pcm of a Chevy Tahoe 2002 and im getting the code p0178 fuel composition sensor.

My truck is a 2002 silverado, why im getting this code cna i just erase it?

 

I'm pretty sure that code is thrown for the alcohol sensor, your truck is a VIN Z correct? Basically means the truck no longer knows the ethanol content of the fuel you are running and will go for as rich as possible on the fuel trims (I think).

The sensor is located near the fuel filter on the driver's side frame rail.