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Discussion Starter #1
I've replaced the thermostat two sensors and my fan still only comes on sometime could it be the AUC sensor please help fan works something is not keeping it on
2004 BMW 545
 

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Are you getting any codes ?
 

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Discussion Starter #3
No codes and I turned the Ac on and the fan didn't come on in the first stage of overheating the fan doesn't kick in the car gets very hot then sometimes the fan will come on
 

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Sorry to hear about your struggles. The AUC sensor isn't in the mix, it is for the heating and air system and senses dirty air and switches the car air to recirculate before those smells enter the cabin.

Do you have INPA or similar setup? Need to read those codes. If thermostat is ruled out then how old is the water pump? A damaged impeller can limit flow. INPA will allow you to manually control the fan in the engine/me9n62 section. Reservoirs is staying full?
 

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Discussion Starter #5
The water pumps works just fine the fan waits until the car is extremely hot then the fan comes on if on this particular it decides to
 

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Google BMW and INPA or go the BMW coders forum. This type software will give you the full list of codes, the guy at Auto Zone will not be able to read our babies. He can pull emission related codes.
**DISCLAIMER** You'll need an older laptop, canbus usb cable, and some technical knowledge and troubleshooting skills.
 

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Discussion Starter #10
I have none of that....hey guys can I get some help please I'm trying not to replace a fan that's working but won't stay on
 

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Man, I'm not sure how long you've owned this car, but it can potentially bleed you dry. I love my 545, but I do my own work.
The cooling fan takes it's orders from the dme (engine computer) without the proper software tools you'll need a Indy mechanic. Otherwise your just guessing and throwing money at a problem. So many systems are interrelated and they all talk over CANBUS.

One more note, what is the temp your reading when warmed up? 221 degrees F is the nominal warmed up temp. In traffic I'll see 226 before the fans spool up hardcore. I've never seen above 226.

This is hot compared to other cars, but these aren't an Accord. 221 degrees Fahrenheit is normal, crazy, I know. I use bluetooth odb2 dongle and Torque on my phone to watch temps.
 

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Discussion Starter #12
I can't see the actual numbers the car first tells me car hit drive modestly and a few more blocks it goes red and tell me to stop driving this has happened many times but sometimes the fan kicks in other times it dont
 

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Man, I'm not sure how long you've owned this car, but it can potentially bleed you dry. I love my 545, but I do my own work.
The cooling fan takes it's orders from the dme (engine computer) without the proper software tools you'll need a Indy mechanic. Otherwise your just guessing and throwing money at a problem. So many systems are interrelated and they all talk over CANBUS.

One more note, what is the temp your reading when warmed up? 221 degrees F is the nominal warmed up temp. In traffic I'll see 226 before the fans spool up hardcore. I've never seen above 226.

This is hot compared to other cars, but these aren't an Accord. 221 degrees Fahrenheit is normal, crazy, I know. I use bluetooth odb2 dongle and Torque on my phone to watch temps.
that temp must be for v8's correct? im assuming the bigger the engine the hotter..

but i believe on i6's normal temp is 97C I've never seen my temp reach over 105C on both of my cars....
 

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Hmmm. I have to go back to the water pump. If your not losing coolant then it's not getting circulated and chilled fast enough. That leaves the water pump since it's your phone mover. From now on is turn it off at drive moderately. These run so hot normally the overheat and damage threshold is really ready to reach. Drive moderately means pull over with this cooling system and aluminum engine.

A bluetooth odb2 dongle is less than 15 bucks and Torque free version will show you coolant temp. With this you can shut her down at 228 degrees, if it gets that hot there is an issue.

Might be worth pulling the pump and looking at the impeller. Something is restricting flow. Sometimes leaves build up between the radiator and condensor, restricts air flow. It's a stretch, but this seems like a larger issue than the fan not kicking on to high. Does the fan go to high if you kick the ac on?
 

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Yeah, eburnz, I'm ordering a 194 degree thermostat from ECS. 221 is so hot, especially as thingd age with over 150k miles these days. :)
 

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Just ordered a Graf water pump this morning. The cooling on this beat is seriously the thing I find myself worrying about the most.
 

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Discussion Starter #17
Today I turned the car on and put the Avon and the fan didn't come on but the car was sitting over night should it come on immediately
 

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Discussion Starter #18
And also I didn't have this problem until that plastic cover under the car came off it's the part that covers the bottom of the car
 
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