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R56 strange coolant temp sensor behaviour- fan stays on
Hello mini owners. First time posting. I have searched a lot of UK and US forums but can't find this specific issue. I'm hoping you can help.
Fault: electric coolant fan comes on high speed mode for 5 - 10 minutes after shut down.
Finally traced to: the coolant temperature digital reading (using this trick: you tube.com/watch?v=KhFTyjIRaBU ) to the ECU is 'lost/overridden' whenever the climate control blower is turned on. This loss of coolant temperature information puts the car into failsafe mode, and switches the electric coolant fan on high speed mode. The same behavior can be simulated by simply unplugging the coolant temperature sensor.
This never happens unless the climate control is selected to on. Either simple warm blowing or proper aircon. Both options have the effect of 'losing' the coolant temperature signal to the ECU.
Does anyone remember seeing or hearing about this strange behavior?
What is worse is that once the signal is lost, it latches, but with no fault code. An OBD tool is needed to erase whatever is latched and return the coolant temperature signal. You can see this actually happening in the video. As soon as this is done the high speed fan stops.
This is a recent fault and the coolant temp sensor has been replaced with new, twice! The car has only ever had one of the two infamous coolant fan speed relays and only one of the two fuses. These are not the issue.
Remove the two spaces in the link above to see video.
Bit more detail: the coolant temperature digital reading will display as designed all the way from ambient to 100C+ and back down again during a long drive. Providing no heating or aircon is selected on the climate control, the electric coolant fan will remain off after shut down.
If the climate control is turned on during any type of hard or soft drive, the digital coolant reading will be lost and replaced with three asterisks ***C (i.e there has been a loss of coolant temperature signal to ECU)
I'm afraid I can't help but I do have a couple of questions about your issue as well as observations of my own when the temperature sensor in my N16 failed (replacing it with a new one resolved everything).
a. Does your fan only come on only after the engine is shut down (as your text suggests) or does it also come on while the engine is running (and climate control has been switched on)?
b. What do you mean with "it latches"?
c. Is your code reader able to read out codes out of all ECU's, i.e. is it fully compatible with BMW/MINI cars?
d. When my temperature sensor failed, it would come and go at random. If it came back, no "clearing" anything was required, the car just worked normal again all by itself (reporting a seemingly plausible coolant temperature, switching off the fan and going back to normal mode). I didn't have a code reader/resetter at the time, but when I got one a year later there were no codes saved in any ECU. Using the "Reset" function within the hidden menu while the temperature was out of bounds had no effect.
By the way: its not three asterisks but three t's (was mistaken, too, at first). :-)
a. this car's high speed fan comes on whenever the coolant temp sensor signal is lost (confirmed in the hidden display menu), or the sensor itself is unplugged. It is happening while driving, idle, or shut down. I believe this is behaviour by design for the overheating failsafe reasons mentioned in OP.
b. Sorry, this may be a UK slang term for fault troubleshooting. A 'latched' fault/error code means it is stored or memorized inside whatever ECU or computer is controlling that piece of equipment. Normally a latched fault needs to be reset or cleared manually. But I know with cars sometimes just driving the car a number of times will self-clear certain faults.
c. Good point. I only have a cheap OBD fault reader. It does work with this mini and has shown correct CAT/Oxy sensor faults in the past that we've had to fix. And it does clear this particular issue at least. I'll borrow a pro code reader and do a rescan. Thanks.
d. OK interesting. You were able to watch the coolant temp reading come and go on the dash? I'm glad the replacement sensor solved your issue. The only thing I can think to do for right now to avoid killing this car's fan and the battery is to have a bluetooth OBD fault code dongle permanently attached. Then just hit the erase button every time the fan comes on. Because we can confirm the temperature is actually fine (less than <105C)
I think you are right! Tiny little t's. But I reckon they wanted to use asterisks - the international symbol of 'data error' :-)
I should have gotten more sleep yesterday before replying:
Since the thermostat housing was of the original design (not allowing the temp sensor come off by itself), the housing had to be replaced as a whole. This I had done at BMW at the time. So any code which had possibly "latched" (used correctly?) was potentially erased by the dealer before handing the car over to me.
Originally Posted by belkindlnk
You were able to watch the coolant temp reading come and go on the dash?
Yes. I had to drive over 2000km within one day before addressing the issue and spent most of that time inside the hidden menu watching the coolant temperature display.
In your case I'd suspect either some ECU fault (in connection with the CAN bus) or some electrical issue. However, I'm a complete layman and have no idea whether this is even plausible, let alone likely. It does however sound difficult to diagnose without diving into ECU interactions and/or checking the wiring. I wish you luck and hope you will have the time to report back your progress.
PS.: If you own an android phone with OTG-USB, I'd recommend the free app Deep-OBD. Not only is it fully compatible with BMW/MINI cars (reporting not just the codes but also the corresponding full text descriptions), it is also capable to report at real time values of all sensors. I use it with a cheap chinese USB-OBD adapter but it is also compatible with Bluetooth-OBD adapters. The downside of it is that it is not immediately clear how to set it up.
I've just downloaded that app. Thank you! I'll let you know how the troubleshooting progresses. Could be useful for other owners once I get to the bottom of this.
Did you ever resolve this?
mine is doing exactly the same.
Hi there. Yes I did, in a roundabout way.
I lived with the fault until one day during the emissions test on the car's last MOT (the annual car test in the UK) the thermostat + housing assembly exploded. At high revs in the test centre. Once all the smoke and excitement had died down I replaced complete thermostat assy which included the housing and new temp sensor.
The high speed mode of the fan has not come on by error since (11 ago months now) . I.e, not coming on after a normal drive.
Likely it was a bad temp sensor, even though previously replaced, or something with the thermostat itself interfering with the sensor? Not to bad a job to change. I managed at the side of the road outside the test centre.
