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Loopy external temperature guage

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PeterE

Member
Surrey
My external temperature guage seems to be obtaining its data remotely from the Tropics. After standing overnight it reads accurately agreeing more-or-less with the readings on our external guage in the house and those in the Mustang and Focus.

Thereafter on a journey, it just climbs slowly into the mid 20s and stays there even if its only 10C outside.

There are a number of posts on other BMW forums about this issue on other models so not unknown.

Does anybody else have this issue, if so a recommended solution apart from sensor change? It was OK when the car was delivered in February.

Thanks!
 
Either faulty sensor or it’s dropped from its housing and is roughing something that warms up. ;)

Car under warrantee right? Either book it in or get it sorted next service.
 
I have never had this problem with my g29 or with the 3 e89’s I had.

Got to agree with ori’s comments :)
 
dr_john said:
I have never had this problem with my g29 or with the 3 e89’s I had.

Got to agree with ori’s comments :)
Click to expand...

I didn’t have it on any of my zeds, but 20 years ago on a Porsche the sensor came out of its housing and would touch the rad. Caused all sorts of strange readings. Sometimes it would just hang in the sun and warm up that way.
 
oddly i noticed mine state 23.5 degrees on drives this weekend when iPhone weather app stated 17. it was warm but not sure it was what the car was stating.
 
Thanks everyone for the feedback/advice, I'll get this looked at when next in for a warranty service.

If I can work out where the sensor is I'll have a look at it, I think on the E89 it is under the front n/s wheel arch but not sure on the G29.

Of course, I don't need a temp guage to tell me when I can lower the roof...
 
Update on this old thread - external temperature gauge issue investigated by Dealer as part of oil change service this week and confirmed as faulty, replaced under warranty.

My battery was low at about 50% too so I need to use the car more and hook up my battery conditioner regularly from now on.
 
Ah, at last I have found others with the same issue.
The thermometer on my M40i also has an ‘optimistic’ approach to life. At initial start up and when pottering around town it reads accurately, but once up to motorway speed the reading begins to rise and ends up being about 6 degrees warmer than reality.
The car has been in to the dealer on several occasions, and the sensor has been changed (no effect), the software updated with a version direct from BMW Technical (no effect) and most recently the ‘combi unit’ (?) has also been changed (no effect).
So it seems that the sensor is working, but is sitting in airflow that is not truly reflective of the outside air. Could it be something to do with the active vents at the front of the car?
So far, nothing has that BMW has tried has had any effect whatsoever.
I thought I was all alone on this one!
 
If it’s any help this is what my Dealer reported that they’d done

:“… NOTES - Investigated into outside temperature sensor showing incorrect reading. Read fault memory and found fault stored for power management. Carried out energy diagnosis, test plan advised 5 hour battery charge to get up to appropriate %. Charged battery and retested.
Disconnect temperature sensor, kombi control unit now reading at -40 degrees, default setting, reset and now showing -5.5%, suspected faulty sensor. Replaced sensor and reset kombi, retested following morning and now showing at correct temperatures...”

They did comment that the battery was only charged to 50% which could affect the accuracy but that doesn’t account for the misreading being evident last summer after a couple of 150 mile runs and the stop/start working which it doesn’t if the battery’s low.

I believe that the sensor is behind the LH front air intake and is a common part used across most BMWs including Minis. I guess it’s possible that this issue only affects the B58 i6 M40s as the engine is appreciably bigger than the B48 i4 but I don’t know.

Mine still reads slightly high compared to an old school mercury thermometer placed near it - when stationary of course - so will monitor closely in the coming months.
 
Thanks for this.
Since the thermometers are reading ‘plausible’ temperatures rather than temperatures that could not possibly be, such as -40 degrees, the most obvious answer ( the Occam’s Razor approach) is that the thermometer is working properly, and it’s the airflow that is wrong, feeding the sensor air that has been warmed either by the engine or the radiator. It never, in my case, reads too low, always too warm.
Please do keep any updates coming.
 
I have the same problem om my 2022 G29 M40i. The outside temp slowly rises to about 6 degree celcius above the right temp.
At the service last summer i complained about vibrating front brakes and the temp problem but they found nothing wrong. I am trying again tomorrow.
 
That sounds exactly the same issue, even down to the extent of the misreading. Please let us know how you get on with the dealer.
 
Service today at Bavaria Skellefteå (Sweden)
They did a new troubleshooting to find the problem with the outdoor temperature sensor.
After test drive, troubleshooting and updating the software, there is nothing wrong with the car!

But they agree that the temperature sensor does not correspond to reality.

So it could be a design mistake. According to the technician, there is more than one sensor that measures the outside temperature and to access them you have to take down the front bumper. Since the warranty on the car has expired and there are no errors that are visible in their computer, they want to be paid if they are going to troubleshoot more.
I'll probably have to take it down myself when I get annoyed enough. It is probably the rubber lip under the bumper that gives some rear suction under the car or something else. :tumbleweed: :-)
 
Thanks for the update. That really supports my view that the problem isn’t to do with the sensor, which is reading the temperature accurately, but it is sitting in air that does not reflect the outside air temperature. This should affect all M40i cars if that is the case.
 
Yes, you are right about that.
Someday maybe the bumper comes of.

The only real problem is that it disturbs the climate system when the car thinks it is hot outside.
 
Does it only affect M40i models? Are there examples of 2.0i and 3.0i models being affected too, which you would expect if it were hardware related wouldn’t you?
If it’s only M40i models then is it related to the active radiator vents closing and disrupting airflow?
 
Mine has failed again after being OK-ish for six months; consistently read between 23-28C on a 200mi run back from Devon last week.

I don't think the external air temp has been near that anywhere in the UK this 'summer' so far and winding down the window I guessed it to be around 19C.

I give up 😤.
 
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