Got Service Engine Soon Light
 

I ended up hooking up my OBD II on it and pulled a code of P0128

"Coolant Temperature below Thermostat Regualting Temperature"

What exactly does this mean. I looked at the coolant level and it was fine. I went ahead and removed the error code to see if it returns.

What would cause the error?

X5 is a 2004 3.0

Two possible things come to mind.

1) You have a thermostat that is sticking in the open position, not allowing the coolant to heat up to operating temperature.

2) Your coolant temperature sensor is going south.

Cool, didn't think about the Thermostat sticking open. Are these easy to change out? Ie; location of thermostat. Also, where is the Temp Sensor located?

If you take off the plastic air intake plate and the clutch fan, the tstat lives in a housing (you replace all of it at once) right there in front of the motor. There are two hoses connected to it. Just drain the radiator, then disconnect those two hoses and unbolt the tstat housing. Installation is reverse of removal.

There are a few write ups around if you search for them.