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Discussion Starter #1
So just as the title states, I'm working on a diagnosis for the e-box fan (located in the DME box under the hood for those who don't know).

I've had the code since the summer time and every time I clear it, it comes back in a short amount of time. I got a used e-box fan I ripped from a junkyard car, so I figured I'd put it in today and see if that took care of it. Well it turns out not all e-box fans were created the same. The one I got was from a 2000 528i. It has three wires (even a heavier gauge) and mine only has 2 wires. Good thing I only paid $5 for it. So now I decide that since the DME box is ripped open, I might as well diagnosis the darn thing the right way. I had already pulled my fan out, so I hooked it up to a battery charger on 12v 2 amp setting. Lo and behold it works. hmm. So why am I getting the code? I started following the 2 wires back to where they lead and figured out (later verified using WDS) that the BR/GN wire goes to the DME and the Red/WH wire goes to a power source in the box, a 30A fuse. I checked all fuses visually and they are OK.

Where to next? Is it possible that even with the fan running the DME sees high resistance and thinks it's faulty? Seems like a pretty simple system, power, ground and a motor in between that's activated by the DME. Does the fan run all the time or is it temp related? I'm about to go out and reconnect the battery and check voltage on those connections with the KOEO and KOER.

Any ideas?

I guess one last idea I have is that maybe the fan does work but when it gets hot is seizes?
 

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I will be very interested to see the opinions raised in this thread. I have in recent weeks also been getting the e box fan code on occasions, although mine is definitely operational and can be activated via INPA/DIS.

I have previously read that the fan blows onto a sensor within the DME itself and wondered whether the sensor might fail and therefore the car sees a false/implausible reading and assumes the fan to be at fault.

Mike
 

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You know Tech this my favorite topic, NOT! Likely the reason you are getting the code is because it is not switching speeds. Why that happens I have no idea, I have not even figured out how it switches speeds, but none the less it does. The DME does something to the ground to change the speed, I believe it is the slow speed that fails. The slow speed is the important one.
Don't ask why it switches speeds or I might tell you my theory and we will have something much worse than an oil thread. LOL
 

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That e-box fan system is one of the more troubling parts of the car, at the time it was built there were plenty of automotive control systems that could easily handle the heat of an engine bay and yet they chose a system that required the fan and it's ancillary support.
 

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I changed out my fan for a brand new one and still have the shadow codes coming back sometimes. At this point it's like the crankshaft sensor codes. I just say meh and move on.
 

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I am pretty sure that is the point. The rest of the car is very up to date so those that think this fan is for cooling are not likely correct. Considering the M3s system is the same and it is know that their system is the main ambient air sensor, here we have to be different.
 

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Discussion Starter #7
So after I posted this I went back out for some testing. First I checked for power on the red/white wire with a simple test light probe. It is switched power that remains on for a little bit after the key is turned off until the circuit goes into sleep. I then plugged the connector back in and back probed the power wire again with the same results. Next I back probed the BR/GN wire. KOEO there is no power at this wire on the connector. Once I started the car I got a really weak bulb lighting up. I thought that strange so I probed with my cheap multimeter. It showed 12v but it must have been really weak amps? Caused by high resistance?

Either way, based on the info given I guess I'll still go ahead and get another fan.

Good news is we're going into winter so I shouldn't have high temps in the DME box anytime soon.
 

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Discussion Starter #9
Just don't clear the code. It is not for cooling but if the code is there the DME will do other things.
Yeah I cleared it right after I was done messing around with it since I was already in INPA checking and clearing airbag codes. (Finally got that sorted!)

My guess is the code will be back today.

So the question is do I bend over and buy a new one for $120 or find a used one and hope that it works on all speeds? - I wasn't concerned about buying a used one until I found out mine still spins!
 

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So after I posted this I went back out for some testing. First I checked for power on the red/white wire with a simple test light probe. It is switched power that remains on for a little bit after the key is turned off until the circuit goes into sleep. I then plugged the connector back in and back probed the power wire again with the same results. Next I back probed the BR/GN wire. KOEO there is no power at this wire on the connector. Once I started the car I got a really weak bulb lighting up. I thought that strange so I probed with my cheap multimeter. It showed 12v but it must have been really weak amps? Caused by high resistance?
Sounds like the DME is introducing a resistance on the ground side of the fan to control fan speed. With KOEO, the resistance was low and so all the voltage drop was across the fan (or at least the voltage in the ground wire was not enough to light the test light). Then KOER, the DME switched to a higher resistance internally and the voltage was now dropping across the motor and the internal resistance so you saw some voltage on the test light.

I'm surprised the multimeter read 12V though. I would have expected less. Does it read 12V accurately?
 

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This will not fix your issue but is pertinent nonetheless.



I6 cars and early M5s use the three wire fan. The fan comes on when the e-box temp gets to 44C and stays on until the temp is equal to or less than 36C.
 

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Discussion Starter #12
Sounds like the DME is introducing a resistance on the ground side of the fan to control fan speed. With KOEO, the resistance was low and so all the voltage drop was across the fan (or at least the voltage in the ground wire was not enough to light the test light). Then KOER, the DME switched to a higher resistance internally and the voltage was now dropping across the motor and the internal resistance so you saw some voltage on the test light.

I'm surprised the multimeter read 12V though. I would have expected less. Does it read 12V accurately?
It definitely reads correctly, and I double checked I was reading the right scale, which it was, but you're still making me doubt what I saw. lol. I expected to see something like 5v or similar. It seems to me that it was something like a corroded wire problem, where it ohmn's out fine but once you apply power/amps it can't handle it.
 

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Discussion Starter #13
This will not fix your issue but is pertinent nonetheless.



I6 cars and early M5s use the three wire fan. The fan comes on when the e-box temp gets to 44C and stays on until the temp is equal to or less than 36C.
Thanks for that. Where did you find this? TIS? I need to learn to navigate that system better. I have it in a virtual computer on my home desktop computer. I never use it but it would be good for getting torques and other specs.
 

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Discussion Starter #15
I am curious about something, when does the light come on? At start or during the drive?
If you're referring to the SES/CEL then the answer is never. That light never turns on, it only sets a code in the DME. It's not a hard fault though because after I cleared the code I cycled the key (waiting the 10-20 seconds for power down) and then scanned the DME again and there were no codes. I guess what I didn't check though is clear the code, cycle key and then start the car, then recheck for codes. So it's possible the code sets as soon as the fan is triggered on.
 

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Can't say I know the SES will trigger on that code. I will have to read some posts. All data says it does, but I read that with a grain of salt. If you can figure out when it is being triggered it would be an interesting data point.
 

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Sailor,

I seem to recall a previous comment of yours (different e box fan thread) that you felt this fan was sufficiently important that it has power even with the starter running.

Is it possible that what it actually has is a ground to the starter - so that it spins up briefly during starting - as suggested above to prevent lock up?

With three cables on the plug, possibly supply, ground to starter and second ground triggered by elevated temperature (35/40 degrees).
 

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The early cars had a wire from the starter so as the starter spun the fan would be powered, but now it is all controlled by the DME. Even now the fan runs during the starter rotation, at least it has the couple of times I have watched. This little quest for me started when a friend that races M3s with factory help, should say did, now races something else. He teased me about the sensor in the DME and showed me the supply to his fan, told me it was important and I should look closer. Then he laughed at me. The only hint he gave me was it is not for cooling.

I have never found the map for it in the DME, I suspect without that I will never know.
 

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That reads to me as though there is a barometric pressure sensor built into the DME to be used alongside the calculated air mass and temperature date provided by the MAFS in deciding fueling for both emissions and performance.

Whilst the DME can probably run quite happily at elevated temperatures, if it did so it would be likely to distort the reported pressure value and therefore a fan is built in to maintain a reasonably even temperature.
 
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