aux fan failure confirmation
 

Just recently completed my cooling system overhaul, and I decided to test temps while the A/C being on. I noticed the aux fan wasn't turning on at all. Even after a roughly 15 minute drive with temps fluctuating between 92-96c. I suspect this is the reason why it snook up to 98c for a moment while at a stop light, without the a/c on. Ambients temps were about 57-61F during the drive.

after some searching here i've tried a few things;

- turned on a/c with the car on; aux fan didn't turn on

- tried unplugging the a/c pressure switch, a/c on, with car running; aux fan didn't turn on.

i'm on the verge of replacing the aux fan myself but i'd to know if there's anything else i can try before making the purchase. Could this be an issue with the wiring harness possibly?

thanks

The fan should turn about 1/8 of a turn every time you turn on the key.

The main test people use is what you did pulling the pressure switch on the AC will make the fan spin full speed.

The proper test is to use a bidirectional scanner like the Foxhall 510 or Foxwell 710, and then you can just command the fan on at different speeds


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Just to make sure. This is the AC pressure switch right?

image

I tried recording a clip of the blades with my phone, turn the key twice, no aux fan response at all.

Yup


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Welcome to the site. The aux fan normally turns on shortly after the A/C is turned on. Buy a brushless replacement. TOPAZ makes a nice one. I have one running for 2 years. It takes almost 32 seconds after cutting power for it to stop turning. Brushless fans are very efficient.

I think you’re supposed to replace it from the below, but I was able to replace mine from above.

Was this with or without unbolting the bumper frame?

Thank you. I think i'll go with that. It's cheaper than the Tyc one that was suggested here too.

TYC fan is from Taiwan, TOPAZ fan may not be
 

When I replaced my AUX fan last August, I went with X5chemist's recommendation of the TYC fan. At that time, it cost $190 at Amazon (where I bought it from, due to Prime free shipping and getting a discount from them), and see that now Amazon lists it for just $170 (a good deal in my book). It runs so quietly/smoothly, that you can't feel or hear it from inside the X.

The TOPAZ replacement fan , also from Amazon, is half the price, at $95, and may or not be of comparable quality, but given the time and effort spent in installing the AUX fan (especially for an old guy, in direct sun, in 100F+ temperatures), once and done was my choice prompting buying a more expensive fan.
Attachment 84817 above & below-bumper pieces removed for the install

I think I'd rather go with a recommended/quality part than try another without a recommendation. Perhaps TOPAZ is just as good, but who knows for sure?

I've never had problems with Taiwan-sourced paerts, but have had several with mainland Chinese-made parts, previously. It all depends on the QC given by the "brand" owner, since many Chinesium parts are first-rate, with ones made at the same facility that are seconds, but acceptable to a differnt "brand" owner. I've got some cheap tools and (many) electrical parts from China, but I try to have back-ups for all, just in case. But, as I stated, I'll not be happy to do another AUX fan install, anytime soon.

thanks for the feedback. i'm always open to suggestions. I'd rather buy once, cry once when it comes to anything involving the cooling or HVAC system. you've got a point. what would be the benefit of a brushless fan otherwise? that had swayed towards the topaz option.

brushless AUX fan (DME controlled) vs. brushed aftermarket fan (w/manual control)
 

I think that all the replacement fans for our X5's are brushless; the DME regulates fan operation via PWM signals that the brushless fans need. Brushed fans just need a potentiometer to change speeds.

Brushless fan motors are also thinner, which helps them fit in tighter spots like between the grille and radiator; I use an aftermarket brushed fan (replacing the stock viscous fan in my '01 X5), and it is thicker in cross-section than the AUX fan.

I use an aftermarket (Chinesium) motor speed controller to adjust fan speed on the high-cfm fan I installed. It can really make a lot of uneccessary noise (and draw more amps than needed) when idling at stoplights or when the airflow thru the radiator doesn't need that much fan speed, so I tune the speed down accordingly. The DME does the same for the (brushless) AUX fan, automatically.

I had to replace the one in my 2002 3.0 in 2022. I replaced it with a Mahle Behr unit which was not cheap then, but has gone up around $200 since. Currently $555.99 at FCP Euro. Ouch. If I were doing it again, I might have to consider something like the Topaz.

FWIW, when my auxiliary fan went, the AC stopped working altogether. I also pulled it from the bottom, which required removing the outer bumper panel. Definitely not a super fun job.

Chris
Lockhart TX
2002 X5 3.0 Titansilber
2005 X5 3.0 Schwarz 2

I had to cut some plastic duct i think to pull mine out the top. I was pretty happy to do it that way. I used aftermarket fan from Amazon cost $100. It wasn't any louder than the og fan.

Mine has a TOPAZ Condenser cooling fan 64546921381. Replaced by removing the bumper.

TYC vs TOPAZ fan: whatever works is fine
 

X5chemist- I thought you recommended the TYC fan, not the TOPAZ??

from my thread segment, concerning replacing the AUX fan (segment begins at post #76)
https://xoutpost.com/1240290-post93.html
Attachment 84821

Alright I've decided to order the TYC fan; should arrive next week. In the meantime though, I shouldn't have any problems driving right? I went to do some errands today and it's still hovering between 92-96c operating temp. Thankfully. The next two days will in the low 70s(F) then it'll be in the 50s for the rest of the week.

I checked my spreadsheet and Amazon history. It’s a TOPAZ. Fans look so much alike. Is the TYC brushless? It might be why I referred to it.

from TYC
 

I own and recommend a TYC fan in the E53..I replaced mine in 2021, and no problems.

TYC is made in Taiwan and comes with a lifetime warranty. Topaz is almost certainly made in China.

BimmerBreaker makes an interesting comment about failed PWM wires in the following thread.

https://xoutpost.com/bmw-sav-forums/...oogle_vignette

I wonder if TOPAZ is the same OEM manufacturer for Audi and VW? Probably not. We know who likes to infringe on copyrights.

TOPAZ is owned by the Shanghai Tongzhi Auto Parts Co., Ltd.

They are an aftermarket parts distributor. They source parts from many unaffiliated manufacturers, almost all Chinese.

They are likely not an OEM provider of much of anything

They are like a Rein in that they make little on their own.

I forgot about that linked post and got mixed up who had recommended the TYC fan (at 74, I guess you could attribute that to a "senior moment"). I have followed recommendations from X5chemist before, and thought it was one of his.

Anyway, the TYC fan I bought is great, and in conjunction with the hi-flow aftermarket electric puller fan I had already installed, both fans make my engine cooling reliable, and A/C cool down to 38F (as measured on 90F days).

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workingonit,
No worries. I keep a spreadsheet to record parts and maintenance. I should probably delete the cost column though.

I quit keeping spreadsheets long ago, when building my dragrace Chevelle and my home-made 4x8 squareback camping trailer. In both cases, it was to hide the truth.

When building the Chevelle, I started building it at home, but my wife found my spreadsheet with costs and future costs, so I quit working on it at home and only did so at my friend's shop, 50 miles from home...out of sight and out of mind of my wife, hahaha. I just resorted to giving my friend/race car builder about $150 a week and he'd buy the parts for me (at a good discount from his ring of sources), and work off the extra costs at his shop every weekend. We'd work on my car, other cars in our race team, and those of his outside customers. The $150 I'd automatically hand over was just some overtime pay I'd always get (for most of 47 years, I was always the first one in and last one out at work, so OT was a given).

On the home-made trailer, I started it out with another spreadsheet, and kept it and the trailer in my friend's shop (after I had quit dragracing), so no worries about the wife snooping and sniping about the costs. But, about halfway through the build (after 11 months), I brought it home into my garage to finish it out (it was a completed exterior shell at the time), and I couldn't hide it anymore, so I just 'fessed-up.

Anyway, I was building it for her to use anyway. She was a member of a Bigfoot hunting group, which would travel to and camp in some wild areas, all over the country; I was wanting a safe, dry, and heated/cooled trailer to replace her crummy tent. So, I showed it to her, and continued to build it in plain sight. When finished, it was too late, as she quit Bigfoot hunting and stayed home, while I took up occasional camping instead (only about 15 days a year, max...much less time than my racing days).

Now, the trailer sits unused in the garage and the Chevelle was traded for the X5 in May of '21. No spreadsheets or secret builds anymore.



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Just did a quick test using INPA setting the aux fan at 30%; no spin at all. I'll be testing the new fan before I even bother removing the front bumper. This car is nerve racking sometimes, but I love it.

Test for voltage on the power cable before you pull the fan.

I was able to plug in my fan on e 70 while it was on top of the motor.

(If fan is disconnected, the water pump runs at full speed).

I had to drill out a couple screws holding the bumper cover. Seized spring nuts just spun.

I used some wall anchors and fender washers to reattach.

Yes, test for voltage before replacing. There is a 50A fuse that can blow. My failed fan turned out to be a $3 fuse.

The fuse always blows for a reason and often because the fan is on it's way out so if mileage on the fan is up there it might be a good idea to replace it anyway.

+1 for sure especially 50A!


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Quick update.

The replacement was a success. Tested the new fan with INPA before removing everything; the fan ran without problems. Ripped everything apart, replaced the old the fan, ran INPA again and the fan worked. Just in time for 80F degree weather.

Thanks guys.

One question though; is the aux fan triggered by the temperature read by the CTS on the lower radiator hose?

I think it does use that sensor. It’s not a simple on off at some temperature. It uses the settings of the AC control and some formula

I tested the hell out of my bad fan before replacing it several years ago. Toughest part as usual was separating internet fact from fiction.

Based on tests on my 2001 3.0i, with an at-the-time dead aux fan ...

Short answer is that yes, it uses that temp, but the engine must be running for it to turn on the fan due to a high temp there, and also just pulling the connector off the sensor does not work since it simulates -54*C. Putting a 100 Ohm resistor across the connector simulates hot enough to turn the fan on when the engine is running.

My notes:
Experiments with the temp sensor on the lower radiator hose
This has nothing to do with the temp gauge in the instrument panel (which uses a different sending unit). No warnings result when the temp varies to extremes.
Tests done with ignition ON, engine not running, battery charger maintaining voltage.
I used the Foxwell to monitor live data on that temperature. Measured about 71*F (ambient temp) when starting.
Disconnected the connector, simulating infinite resistance ==> -54*F
Measured resistance of the sender = 2.8 kOhms
Put the following resistors across the connector to simulate different temperatures:
temp [F] resistance [kOhms]
-54 infinity (unplugged)
71 2.8 (actual sensor)
94 1.48
122 0.80
159 0.40
213 0.151
241 0.100

These were done to confirm how I could simulate an overheated radiator hose, to hopefully trigger the fan to turn. Interweb lore says that you can just unplug the sensor, but that does not seem to work, which makes sense. The 100 Ohm resistor simulates 241F, and successfully triggers the fan to come on (the command comes, even though the fan does not spin).

Monitoring voltage on the fan control wire from the ECU:
Ignition ON, engine stopped, battery charger maintaining voltage at ~14V

Normal state - 14V (It is a square wave, but the DC Voltage meter showed this solid value; switching to AC gave numbers bouncing between almost that and zero; implying the DC reading shown is an integrated average)

Foxwell active test of the fan - almost instant drop to 1.6V, holding for 20 seconds. So 14V means fan is commanded off, 1.6V means it is commanded full speed on.

Putting the 100 Ohm resistor to simulate 241F at the lower radiator hose - no effect on fan control voltage. (but will have effect when engine is running)

Now started the engine, AC off.

100 Ohm resistor to simulate 241F at the lower radiator hose - control voltage gradually dropped to 2.6V over a period of about 30 seconds. This would gradually ramp up the speed of the fan to almost full speed. Repeating, this response did not happen with the engine stopped.

aux fan failure confirmation
 

That's some great detail! So with a working fan, rather than attempt to generate a square wave you can dial-a-temp using a potentiometer across the sensor leads. You could run in parallel just use a high enough Ω potentiometer that the effect is negligible when set high.

Fascinating :-)

Can you control the speed or it just goes max when hits the magic overheat value?

Which fan brand was installed? Curious minds want to know. :bmw:

It was a TYC branded fan. I'm hoping to get several years out of this at least.

Pulling the coolant or A/C high pressure connector, engine running, even with A/C off, works to get mine running. Pulling the A/C connector to test would be what I recommend.

Lifetime warranty...Keep your receipt and the warranty -which you can download/print off the Amazon website- where you can find them.

But i bet that fan will last longer than the car.

Congratulations
 

Good question, those notes are better than my memory at this point. Doing those tests, I was mainly trying to be sure the fan was bad before buying a replacement, rather than to figure out extra details. I think if the next lower temp had triggered the voltage to change, I would have noted that. Since I did not, it probably did not trigger.

Knowing how BMW likes to run these engines hot, and having a coolant thermostat, I would not be surprised if the fan just turns on at some high enough temp, and stays off below it (unless AC is on). So that's a guess.

I agree on the idea for this being an input for active fan control.

I used a TYC fan. Seems great, no problems.

I agree. When I did all those tests, it was partly because so much of the info on the intertubes was contradicting itself, so it was tough to believe anything.

Here are my notes on the AC in general, and the AC pressure sensor in particular. As above, the main thing I was looking for was confirmation that the ECU was working and the fan was broken.

AC turned on

Control voltage gradually dropped to 13 ... 12 ... 11V, holding there. I expect this would be spinning the fan at least a little, as soon as the AC came on, and would regulate speed based on something currently unknown (e.g., some AC system measurement, radiator hose temp)

AC Pressure sensor - in AC line very close to the lower radiator hose. Measured in Foxwell:
Ignition ON, engine stopped, AC off, cold: 1.25V
... connector removed: 5.00V
Engine running: 1.24V
Engine running, AC on: 1.76V, rising
... connector removed: 5.00V

When the AC was turned on, the fan control signal dropped to 12 .. 11V, as before.
When the AC pressure sensor connector was removed, it very quickly ramped down, at about one Volt per second, ending at about 2.0V, which should be almost top speed for the fan.

As for the lower rad hose sensor, the DME is not seeing the disconnected sensor as reading a "low temp" but as "disconnected" and would then likely run the fan as a failsafe. I didn't spend a lot of time checking, but with the coolant sensor disconnected the fan ramped up to about 1/2 speed (DME still knows engine temp) and with the A/C sensor disconnected ramped up to high. Both ramped back down when re-connected. What is the reason for wanting adjustable active fan control ??

For my 2001, the disconnected rad hose sensor caused my Foxwell to show the temp as -54*F. Maybe the ECU considers this as disconnected.

[mention]workingonit [/mention] i think replaced both his fans with one electric akin to e seventy.

So he uses speed control to get an appropriate amount of air moving as needed. I don't remember if he automated the speed or it's based on temp reading.

all-electric fans on my pre-facelift E53
 

In 2021, just after I swapped cars for the E53, I had to replace the viscous clutch fan, because the clutch was going out, and the blades were deteriorating. I used a 3000cfm aftermarket electric fan (brushed) and a thermostatic switch + override switch to switch it on, at first, then added a speed controller (for brushed fans) in-line, so I could control the fan speed from zero to 100%, as needed, from my driver's seat. Never touched the Auxilliary fan, which was working fine.

But, three years later (in 2024), the Aux fan quit working, and I installed a TYC fan in its' place. All is well, now.