OBD trouble code 178

I have 2002 Tahoe. The Service Engine Soon light came on a few days ago. I carried to a local garage for diagnosis. Their computer showed code 178, which translates into Fuel Composition Sensor Low Voltage. The mechanic indicated he had never heard of that before and didn't have a clue what to do for it. Can anyone offer advice? Is there a sensor I need to replace or is something else causing the problem? Also I might note that the fuel pump was replaced a month ago. Could that have something to do with the problem? Any help will be appreciated.

you should take it to a gm dealer and see if you can get warranty for this since it's emmisions related. anyways there is a sensor that the fuel lines connect to up near the steering box and it is used to measure both alcohol content and temperature of the fuel. there is a 3 wire harness going to the sensor. testing the sensor takes some fancy tools so it is best left to the dealer.