can anyone tell me what error code 4SNS/1/40000000TBIT-128.000 means for macpro 2009

It means there has been a sensor failure. I'm not positive about the BIT part since Apple does not provide that information but I think it is referring to a temperature sensor. B may refer to battery in which case I don't know what the IT means.

It looks like a heat sensor of some sort

I expect that it's TB1T : an internal battery temperature sensor, which isn't being detected.