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7 Series - E65 / E66 (2002 - 2008)
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  #1  
Old 01-24-2012, 10:24 AM
Dmurry101 Dmurry101 is offline
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I am getting a code P0128 again

I have a 2004 BMW 745LI I am getting a code P0128 Coolant Temp Below Thermostat Regulating Temp on my scanner....

After replacing my thermostat my check engine light is coming back on yet again with the same fault code P0128 I use the thermostat from the dealer and I am a little lost on what to do next. Can anyone help with this problem?
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  #2  
Old 01-24-2012, 10:54 AM
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USALEXUSBMW750 USALEXUSBMW750 is offline
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Probably temp sensor acting
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  #3  
Old 01-24-2012, 12:09 PM
Dmurry101 Dmurry101 is offline
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where can I find that?
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Old 01-24-2012, 09:11 PM
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roadfrog roadfrog is offline
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It's built into the housing with the thermostat that you replaced already. Weird. Pretty unlikely that it's a faulty assembly, but I'd start with that. I had the same error and it was gone permanently after I replaced the unit. Here's some more info:

A code P0128 may mean that one or more of the following has happened:

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
Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:

Verify coolant strength & level
Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
If the above items check out good, replace the thermostat

Last edited by roadfrog; 01-24-2012 at 09:23 PM.
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  #5  
Old 01-25-2012, 07:17 AM
Dmurry101 Dmurry101 is offline
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Thanks a lot.... Im going to get to work on that this weekend
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  #6  
Old 03-06-2012, 10:53 AM
freddyb freddyb is offline
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I am having the same issue with my 7. I recently replaced the temperature sensor because it was leaking. After I replaced the sensor I started the vehicle and the light went off briefly but came back on. Were is the air temperature sensor located also what is the process for checking the operation of the air temperature sensor and fans.
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Old 03-06-2012, 12:11 PM
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pkathee pkathee is offline
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Quote:
Originally Posted by freddyb View Post
I am having the same issue with my 7. I recently replaced the temperature sensor because it was leaking. After I replaced the sensor I started the vehicle and the light went off briefly but came back on. Were is the air temperature sensor located also what is the process for checking the operation of the air temperature sensor and fans.
Freddy,
Just a FYI, next time you find out that your temperature sensor is leaking, no need to replace it. The leak is usually caused by a faulty O-ring gasket. It fails by deteriorating and becoming brittle over time and thus coolant start leaking.

That said, instead of spending a whole $50 on a new temperature sensor, you could have easily ordered a replacement O-ring for like $0.99. That should have fixed your leaking problem....I barely did that like a couple of months ago.
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