DME and aux fan error

[PalmSpringsE534.6]

Hi everyone,

My E53 seems to be hungry for new parts again. LOL. Been having issues with the aux fan not working even after repaired. Turns out that the DME is sending "some" signal but not the right signal to activate the fan. Saw the scope and it's definitely not a square wave...so, I have a choice to make.

1. Send out the DME for a repair/rebuild...though the fan circuit is all that is out at this time
2. Indy suggested we put in an electric aux fan and a relay that will kick it on when the AC is activated.

Is there any downside to having a fan run anytime the AC is on? I'm not an AC specialist. I'm not against fixing the DME but I must admit that I find it attractive to replace the PWM fan with a simpler solution.

Pros/Cons appreciated so I can make an educated decision to stay stock or to make a change to my vehicle operation.

[X5chemist]

Depends on your driving. A daily driver will eventually burn up the fan. Above 30 MPH, most condenser fans turn off. A trinary switch would work. I've installed trinary switches on A/C high pressure lines. Unfortunately, our E53s don't have a shrader valve port. A trinary switch would simply screw on.

Does anyone know how the pressure switch works? You could grab a relay signal from there.

[PalmSpringsE534.6]

Originally Posted by X5chemist

Depends on your driving. A daily driver will eventually burn up the fan. Above 30 MPH, most condenser fans turn off. A trinary switch would work. I've installed trinary switches on A/C high pressure lines. Unfortunately, our E53s don't have a shrader valve port. A trinary switch would simply screw on.

Does anyone know how the pressure switch works? You could grab a relay signal from there.

You just helped me make up my mind. I'll pull out my DME and send it out for a repair and simply reinstall it. Found a DME repair service for $275...so I think I have my answer. Hadn't thought about this long enough to realize that living in the desert, the AC would be on almost all the time. That would likely burn up a fan and create more issues in the long term.

DME repair here I come. Heck, had the ABS unit rebuilt so maybe the DME was just not feeling the love. LOL.

[X5chemist]

LOL, good info helps make decisions. Who is rebuilding your DME? I may need rebuild my GM3. So far, I keep hitting dead ends on no sleep mode. Sending out the GM3 may solve my issues.

[PalmSpringsE534.6]

Originally Posted by X5chemist

LOL, good info helps make decisions. Who is rebuilding your DME? I may need rebuild my GM3. So far, I keep hitting dead ends on no sleep mode. Sending out the GM3 may solve my issues.

I'll probably use these folks: https://www.g7computers.com

I used a firm in SoCal to do my ABS rebuild last year but they don't do ECU/DMEs.

[Clavurion]

So you already checked the connectors on DME so there is no corrosion on pins? Very rare that PWM circuits fail on any BMW engine ECU.

[oldskewel]

Is there a reason your indy did not just plug the new fan in to test it before ripping out the old one and putting in the new one?

I literally did that last night, when finally getting around to fixing this issue on my x5 (where we live, an aux fan is not as critical as it is in most places this time of year, so I've been putting it off for a long time).

There are many ways to actively get the ECU to turn the fan on, but for me it was easiest to command the active test using my foxwell. It spun it up gradually and then held it at full speed for a while before letting it back down. Prior to buying the new fan, I tested the system thoroughly to make sure the signal was being sent, but the fan was not doing its job. There is another thread on here where I provide a ship ton of info on that.

Of course, the foxwell commands go through the ECU, so if you really do have a problem with the ECU or the wiring, failure will not be conclusive.

BTW, that fan (I got a TYC - about $150 at RockAuto.com, highly rated) is incredibly powerful. I would similarly be concerned about having it set on full speed all the time the AC is on. I joked with my kids after opening the box that I was going to install a propeller on the front of the x so it would go faster, and now realize that's not completely joking.

So if your indy could have done that test but does not have a good reason why he did not, I'd factor that into any further consideration of his advice.

Good luck.

[Effduration]

Originally Posted by oldskewel

Is there a reason your indy did not just plug the new fan in to test it before ripping out the old one and putting in the new one?
.

+1 on this

I also recently replaced my aux fan on my ‘05 X5 3.0…

I tried to activate my old on with INPA…NO LUCK..

I also bought the TYC fan on Amazon.. tested it before install and it fired right up.

[80stech]

If the DME is really at fault, it's likely the result of some testing/jumpering by someone not knowing what they are doing.

[Effduration]

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