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Overheat message, no CEL error code

Tiny
RAJDEEP
  • MEMBER
  • 2005 BMW 745
  • V8
  • 2WD
  • AUTOMATIC
  • 155,000 MILES
This is regarding the car listed above 745LI. I have recently changed coolant thermostat, upper and lower coolant sensor and radiator fan. I keep on getting Engine overheated at 107C. The Water pump is working fine as I can see a steady stream of coolant in coolant reservoir. The coolant is between Min and Max range (no coolant leak).

Upper radiator hose is hot and lower radiator hose is warm to touch.

I am able to drive for 30 minutes continuously and the message keeps on popping and disappears and this cycle continues.

Also the radiator fan does not come on when the overheating message pops up. Only when I start the A/C, the fan starts.

Any help is demystifying this issue is much appreciated.

Thank you.
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Tuesday, November 17th, 2020 AT 10:55 AM

28 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
You only have one fan correct? From what I remember this was one large fan and not two smaller fans? If that is the case, we need to figure out why the fan is not coming on. If this message is coming on, that fan should be on high. So if we solve that then I suspect this message will stop coming on.

Do you have a scan tool that can monitor the DME module? We need to see what the module is seeing as temp on these sensors. Since they are new, and it is no change we can assume they are not the issue. So if the fan works when the AC is on then the fan is not the issue. If you replaced the thermostat as well, the only thing really left is the module but I would like to confirm this before we replace it.

Let me know and we can go from there. Thanks
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Tuesday, November 17th, 2020 AT 12:40 PM
Tiny
RAJDEEP
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  • 20 POSTS
Thanks for your prompt response. I do have Foxwell scanner not sure if it checks coolant temperature sensor readings. I will do some tests today. Also does the DME module is change as 1 piece or there fuses that can be replaced?
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Wednesday, November 18th, 2020 AT 6:17 AM
Tiny
KASEKENNY
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Okay. Yeah that would be good if it does. If you want to get some screen shots of the info it has I can help if you are not sure.

Also, I attached the picture of the DME and it is not something that has replaceable fuses or relays.
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Wednesday, November 18th, 2020 AT 6:18 PM
Tiny
RAJDEEP
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  • 20 POSTS
I used BMW INSTA app and the coolant temperature is 107 C and coolant temperature at radiator outlet is 75 C. It keeps falling then again goes up. The main coolant temperature is at 107 C at idle.
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Friday, November 20th, 2020 AT 7:25 AM
Tiny
RAJDEEP
  • MEMBER
  • 20 POSTS
Triggered the electric fan at full speed from ISTA APP.
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Friday, November 20th, 2020 AT 7:38 AM
Tiny
RAJDEEP
  • MEMBER
  • 20 POSTS
Also, at idle the overheat message did not popup. The car was idling around half hour. I drove the car for around 20 minutes and the overheat message popped up.
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Friday, November 20th, 2020 AT 8:07 AM
Tiny
KASEKENNY
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I think you have a restriction in the system. 107 C is a little high so I just want to confirm that the fan is coming on at this point? Or when you say it is triggered, that means you are commanding the fan on with the tool you are using?

If you command the fan on and it comes on but it is not coming on when it is reaching that temp then that is a concern as well.

So let's try and eliminate one of the two of these issues, restriction or fan issue. If you can command the fan on, can you drive the vehicle and see if the message pops up while the fan is running? If it does not then we have a fan issue. If it still comes on, then we have a restriction in the cooling system. The fact that it doesn't overheat while sitting still at idle actually points to both issues so we need to try and eliminate one.
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Saturday, November 21st, 2020 AT 6:53 AM
Tiny
RAJDEEP
  • MEMBER
  • 20 POSTS
The fan comes on only if I turn on the A/C or command it thru the BMW ISTA software. It does not come on otherwise. When temp is 107C and A/C is "off" the fan does not come "on".
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Monday, November 23rd, 2020 AT 3:53 AM
Tiny
KASEKENNY
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Okay. That is the issue we need to deal with first. You have two sensors that could prevent the DME from turning on the fan that is the upper and lower temperature sensors. If you have replaced these and the fan works when the A/C is on, then I would replace the DME. It just does not appear to be commanding it on so when you take its place with the scan tool, it turns on then the DME is not doing it and I would replace it.
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Monday, November 23rd, 2020 AT 7:49 PM
Tiny
RAJDEEP
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Okay so if I get a exact model used DME, do I still have to program it? If so what are my options?
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Tuesday, November 24th, 2020 AT 3:38 AM
Tiny
KASEKENNY
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The manual does not specify what programming will do other then it needs to be programmed so I can't tell you for sure but it appears you cannot use a unit out of another vehicle. The reason is, part of the programming is for the immobilizer unit. This means you need to program the keys to it so that the security system does not prevent the start of the engine. This may just be a back up of the theft system and not matter but based on this, I would not try and use a used module.
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Tuesday, November 24th, 2020 AT 6:26 PM
Tiny
RAJDEEP
  • MEMBER
  • 20 POSTS
I did change the thermostat, thermostat sensor, lower radiator coolant senor and radiator fan. But I haven't erased the error code. Is it a must to clear the error code or would the ECU automatically clear it? Would the pending error codes for thermostat sensor and lower radiator thermostat sensor throw overheating message?
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Wednesday, November 25th, 2020 AT 8:44 AM
Tiny
RAJDEEP
  • MEMBER
  • 20 POSTS
So after clearing the code, I drove for an hour, and no overheat message. The coolant temp hovered between 105 and 107C. Is this normal?
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Thursday, November 26th, 2020 AT 3:07 AM
Tiny
KASEKENNY
  • MECHANIC
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That is a little high for me, but if it operates and does not get higher then I suspect that is normal for this vehicle. I am finding a lot of indication that the normal operating temp is from 99 to 107 C so if you have no issues, codes, or warnings I would leave well enough alone.

This is great news. Keep us posted if anything changes. Thanks
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Thursday, November 26th, 2020 AT 7:52 PM
Tiny
RAJDEEP
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Greatly appreciate your help. God Bless.
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Friday, November 27th, 2020 AT 3:44 AM
Tiny
RAJDEEP
  • MEMBER
  • 20 POSTS
Day 2 no issue. Also the radiator fan has started on normally without A/C turned on. Very strange that error codes were turning on the heating message even though physically all components were doing their job. Will post a final update after the weekend if I am out of the woods.
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Friday, November 27th, 2020 AT 9:29 AM
Tiny
KASEKENNY
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Sounds great. That is weird. Normally these modules don't have glitches like that but it appears that it did. Thanks again.
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Friday, November 27th, 2020 AT 10:52 AM
Tiny
RAJDEEP
  • MEMBER
  • 20 POSTS
I spoke too soon, after around 100 miles of driving the engine has overheated message appeared again.

The coolant temperature stays around 107C. Absolutely no sign of overheating (no steam or leaks). Car drives fine (no loss of power or limp mode).

Please advise. Thanks
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Sunday, November 29th, 2020 AT 12:10 PM
Tiny
KASEKENNY
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Okay. We need to check the fan operation again. I think that is the issue. When the fan doesn't run this message comes on at 107. This temperature is the max temperature which is why the message is coming on and it will overheat if the temperature doesn't come back down. So this takes us back to the DME not commanding the fan on. So let's confirm the fan is not running again and we need to address that.
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Monday, November 30th, 2020 AT 7:04 PM
Tiny
RAJDEEP
  • MEMBER
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I was able to command the FAN to on via a BMW diagnostics OBD2 software called ISTA plus. I was able to trigger the fan to full speed for 30 seconds.
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Tuesday, December 1st, 2020 AT 8:44 AM

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