I have a 2006 R53 Mini with 118K miles.
A PO128 fault appears every few days for the last several months. My engine coolant temperature rises very slowly.
I have replaced the thermostat, thermostat housing, and coolant temperature sensor.
The auxiliary fan runs on high speed as soon as the car is cranked and stops only when the car is turned off.
Any help would be greatly appreciated.

 

Going to move this the Gen1 Stock Problems/Issues area.

First, your the fan resistor may be shot which is why the low speed fan does not work. Wondering if the high speed fan relay is stuck. Do you still get he 0128 after replacing the temp sensor?

and, welcome to NAM, hopefully we can be of assistance.

 

Thanks for the reply. Yes, the P0128 still returns after replacing the the thermostat, thermostat housing, and coolant temperature sensor.

 

I am too lazy to look up someone else fault code if he does not bother to post. I don't store a fault code table in my 2 cell brain. I will guess the DME must think the engine is about to melt down and turn on the high speed fan. You might want to check the wire of the temp sensor all the way back to the DME. It might be severed.

 

I think 0128 is a low temperature alarm, which in this case is odd. The temperature sensor is the normal fix but appears it was replaced and still a code.

 

P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
A code P0128 may mean that one or more of the following has happened: Low engine coolant level Leaking or stuck open thermostat (likely) Faulty cooling fan (running too much) Faulty coolant temperature (ECT) sensor Faulty intake air temperature (IAT) sensor

It looks like it is related to the high speed fan coming on all the time but I cannot figure out why this is happening. It does not seem to be the symptoms of the common problem of the low speed fan resistor going out.

 

It is an indirect way of the ECU saying "my thermistor is reading temperature way too low, so I don't trust it as it very well has gone kaputt". It then turns on the high speed fan per the principle of fool-proof design.