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Discussion Starter · #1 ·
I have a 2005 645CI. I understand that P0128 is a thermostat regulating temperature error. Does anyone know:

1) What is temperature that will set this code?
2) What is the run time at which this temperature threshold is measured?

I realize everyone may say if it is setting the code I have to change the thermostat, but I want to use a lower temp than the factory 105 deg C and need to know the above to determine the temperature I will set with my thermostat.
 

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This is an electronic thermostat, & only BMW OEM is recommended. There have been some threads of others trying to change the temp, but I don't think that there have been many gains. The thermostat usually sets a soft code, that does not set a P code. It could be set by any of the following below.

* Low engine coolant level
* Leaking or stuck open thermostat
* Faulty cooling fan (running too much)
* Faulty coolant temperature (ECT) sensor
* Faulty intake air temperature (IAT) sensor
 

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I replaced the thermostat in my 2008 650i convertible after getting the P0128 code ( took 20 minutes from start to finish, very easy), and no more code or engine fault. :)
 

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Discussion Starter · #4 ·
I realize the stock thermostat will not set a P0128 code. I installed an ECS 90 deg C thermostat. It Is running about 192 deg F which is 88 deg C and warming up quickly as you would expect up to that temperature. It is setting a P0128 code. I would have thought this was warm enough not to set the code, but alas the code comes anyway. If I can determine the parameters for which the code is set I can "tune" or "shim" a stock unit to open a little sooner than 105 Deg C (221 deg F). 221 deg F is too hot for any engine. BMW pushes the envelope to eek out an insignificant amount of efficiency. I personally believe this running temp contributes to rubber seal failures especially the valve covers and valve seals. Something closer to 200 is more reasonable.

There is a specific temperature and time for this to set, I just wonder if anyone has cracked the code to determine these settings.

1) Does anyone know what time and temp sets a P0128?
2) Has anyone cracked the PCM code to program out a P0128 code? It is common in other vehicles and manufacturers to set a similar code and aftermarket companies have hacked the code to be able to "turn off" this test and prevent the code from triggering.
 
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