lpg gauge not working

I have a Ford lpg car and about a month ago the gas gauge light started to flash and indicated that there was no gas left in the car even though I just filled up the tank a few days ago. I brought the car to a service centre to check and they found an error code and did some re-wiring, it only worked for a week or so then the same problem came back again. The gas tank is full but the gas gauge will give me false information that sometimes it shows empty and the next minute it shows that there is about 300kms to go, then the next minute it shows only 40kms to go, you get the point. It has caused me the trouble of actually running out of gas on the road and had to get the car towed because the gas gauge showed there are still plenty of gas in. I was told that the gas gauge needs to be replaced, is this the case? or is there anything else could have cause this or need other fixing?
Thanks!