I cannot get rid of the Code P0128 "Coolant Thermostat Coolant temp below thermostat regulating temp". I am on my 4th mechanic. Thermostats replaced 3 times, temp sensor, water pumps (secondary pump done at the dealer) even my radiator. I had it finally at the dealer who said it was the Aux water pump... $1,000 later, SES light on with the same code. has anyone seen this as a persistent code? I have had the car at a local mechanic, 2 independent BMW only shops and I have another follow up at the dealer as they didn't fix the problem. My car has 155k miles on it. Still runs like new and there are no problems with the water temp itself. It did seem to warm slowly a few months ago when the code first appeared but seems normal now. I did have the code for the secondary air pump but I have installed Shark software to ignore that code rather than machine the exhaust manifold. One of the indie mechanics suggested that secondary air pump may trigger this coolant code. I have never heard anyone on here ever mention that and they don't seem to be related other than the fact that the secondary airpump only operates for a short time when starting the car and the coolant temp would only be low when starting the car. Anyone have a solution?