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Discussion Starter · #1 · (Edited)
To say I am confused is an understatement. First in Real OEM and WDS my car should have a four wire fan, it is a feb 2000 car. It does not have four it has 3 wires (yes on both sides of the plug) it also does not have fuse 7 nor 22 only 20 and of coarse 75. From what I have found it is wired like this
Text Diagram Line Parallel Plan


This is where I am, My fan does not run period. It spins freely and an ohm meter on the power and ground show a closed circuit. It goes to zero. The ohm meter shows an open circuit from the control wire to both the ground and power. Stays at 1.

When I first went at this the fuse was blown, but with some patience it was replaced and has not blown. The plug(@fan) now shows 12v with the AC on and the control wire shows 3+v. I have unplugged the temp sender in the lower rad hose and jumped the pins (on plug) no change. Is that a valid test of the temp sender as its part of the circuit? As I write I realized I never checked the volts of the control wire when I did this, darn. I have jumped 12v to the fan and applied 12v to the control wire all at the same time not a thing happened.

Have I missed anything? Fan and the control are one part? How come I have a three wire system? Was that a change made with the recall?
Seems I need a fan, but which part number goes with the three wire system? I am hesitant to order one based on the month and year of production.

Edit: could a bad ambient air sensor have anything to do with this. I have noticed it jump to the intake air temp at times?
 

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To be honest, when testing the aux fan we usually activate it via a test plan in the GT1 or ISTA and ensure that it operates at the various speed setpoints. One sure-fire way to get it to come on is to idle the car and turn on the A/C. The aux fan should turn on shortly thereafter (especially if the coolant is warm).

Given what you've stated, though, I'd wager that the fan is shot. Typically with proper voltage on terminal 30, a good ground (you did test the ground, right?), and any voltage on the control line you should get some activity.

As for 3 vs. 4 wires, where are you seeing a 4 wire specification in RealOEM? Based on what I just looked up the fan assy p/n should be 64 54 6 921 395 and a quick cross-check with one of my parts suppliers verifies that.
 
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I was looking at part numbers yesterday, and my understanding is that 64 54 6 921 395 supersedes all other pns for E39 aux fans, both pre- and post- 2000. I'm not sure that matches other posts here but I found the same thing on realoem and a couple other sites.

GL

dj
 

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My fan didn't work and tested similarly. It turned out that the resistor pack was shot. I bought a new fan with a new resistor pack and it then worked perfectly.
 

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Discussion Starter · #5 ·
Thanks for the help guys appreciated, after 4 hours of screwing around last night on a job that should have taken 20 mins I was a little more than frustrated. Today I opened my mind a bit and came up with a better approach to searching. It appears I was not the only one from Ontario following bad info. This guy had the same problems with diagnosis as I did.
http://www.m5board.com/vbulletin/e3...iliary-fan-relay-not-working-post1562504.html
Very good thread and good info. There is so much bad info out there on this topic. As best I can tell there is no resistor pack ever in the M5 in the USA, but that is offered by BMW for all model years.:dunno: In place of the resistor there is a solid state controller, nice pic in the thread I linked to. I am going to rip mine out tonight and dissect it. I have one on order from a friend that has a Euro wrecking yard.

I don't have the 35 code either and so far I am guessing that is the code that should tell me that the controller is toast, because there are no relays in this system. I am going to do my best to write a proper path for diagnosis once I repeat the other problems found in the link.
 

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Interesting. That picture is just of a splice point. It looks like the M% fans use a PWM signal to vary the speed, not the more pedestrian resistor pack ;)

Assuming that the wires are in good shape, if the fan's don't work it is time for a new one.
 

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This is one of those time where a DVOM can be misleading. Checking resistance values across a wire path
only indicates continuity. What is needed is to actually test the current carrying capacity of the circuit by
applying a known load across the circuit. If you have just one strand remaining in the wire, it will test OK
with an ohmmeter but it will not carry enough current to supply the demand from the applied load.

To simulate a load, with a good visual indication, make yourself a set of test lights that will draw various
loads, such as 5, 10 and 20 amps. For the various "loads", get a few 1156 lamps from your auto supply
and by wiring different numbers of them in parallel, with 2-3 foot leads, you will then have known test
loads that you can insert into a circuit. Along with the known load, you will also have an immediate visual
indication from the brightness of the lamps as to how well the supply circuit is performing. You can either
solder the wiring connections to the lamp base, or buy some replacement sockets that already have the
wire leads attached.

For the problem at hand, remove the connector from the fan assembly and put your test light across pins
1 and 4 of the supply-side connector. This will test the entire circuit, from the fuse all the way through the
ground path. Any failure in the wiring circuit be seen immediately. If the lights are burning brightly with a
25-30 amp load, you can rule out the supply wiring and the ground path, as the source of the problem.

Regards,
Alan
 

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Discussion Starter · #8 ·
This is one of those time where a DVOM can be misleading. Checking resistance values across a wire path
only indicates continuity. What is needed is to actually test the current carrying capacity of the circuit by
applying a known load across the circuit. If you have just one strand remaining in the wire, it will test OK
with an ohmmeter but it will not carry enough current to supply the demand from the applied load.

To simulate a load, with a good visual indication, make yourself a set of test lights that will draw various
loads, such as 5, 10 and 20 amps. For the various "loads", get a few 1156 lamps from your auto supply
and by wiring different numbers of them in parallel, with 2-3 foot leads, you will then have known test
loads that you can insert into a circuit. Along with the known load, you will also have an immediate visual
indication from the brightness of the lamps as to how well the supply circuit is performing. You can either
solder the wiring connections to the lamp base, or buy some replacement sockets that already have the
wire leads attached.

For the problem at hand, remove the connector from the fan assembly and put your test light across pins
1 and 4 of the supply-side connector. This will test the entire circuit, from the fuse all the way through the
ground path. Any failure in the wiring circuit be seen immediately. If the lights are burning brightly with a
25-30 amp load, you can rule out the supply wiring and the ground path, as the source of the problem.

Regards,
Alan
That is an excellent idea and would add to my collection of other useful hand made tools. You are always a wealth of good info and I look forward to reading your posts. Sure beats what I tried last night which was to short a 30 amp fuse across them. I have 30 amps to the plug but am not sure what is going on past that. Definitely nothing on the control wire from plug to controller. But the 3v from dme to plug seems right because the coolant temp was about 90c and the ground speed was zero.

Have read now that if the controller goes on the low speeds the high usually stays until a demand for it to come on. Then the high load starting from zero blows the fuse and then what is left of the controller. At least on 740i and 750i they use a similar set up.
 

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Wiring tests

That is an excellent idea and would add to my collection of other useful hand made tools. You are always a
wealth of good info and I look forward to reading your posts. Sure beats what I tried last night which was to short a
30 amp fuse across them. I have 30 amps to the plug but am not sure what is going on past that. Definitely nothing
on the control wire from plug to controller. But the 3v from dme to plug seems right because the coolant temp was
about 90c and the ground speed was zero.

Have read now that if the controller goes on the low speeds the high usually stays until a demand for it to come on.
Then the high load starting from zero blows the fuse and then what is left of the controller. At least on 740i and 750i
they use a similar set up.
The greatest value of inserting this 25-30 amp test load, as stated previously, is that it verifies the current carrying capacity under a
"sustained load", plus it tests the entire current path, right down to the grounding point. Verifying, that an adequate ground exists, is
often the most overlooked factor in the trouble shooting process.

In addition, with a test load in place, you can then perform voltage drop (series resistance) testing across each section of current path.
For this circuit (with the test load light across pins 1 to 4), there are three components. First, is the supply cable from the fuse block to
pin #1. Second, is the test load across pins 1 and 4. Third, is the ground path, from pin 4 to ground. For the first and third components,
there should be a maximum of 0.1 volts DC across each of their entire paths. If there is greater than 0.1 volts DC, this indicates excessive
series resistance exists in that section of the current path while it is conducting current, either from a loose/corroded terminal, partially
cut or damaged wire, or the wire size was too small to begin with. Across the test load (second component) it should be reading full
battery voltage, or the same value you would read if you were to place the DVOM test leads between the terminal of fuse 75 and ground.

Testing of the third component is easiest, since the test leads from your DVOM are long enough, so let's start there; Set DVOM on DC Volts
and place the positive lead on pin 4 and the negative lead on the main ground terminal located on top of the right strut housing. If it's
greater than 0.1 volts, move the negative test lead to each of the two ground terminal bars that are bolted onto studs located just behind
the passenger side air filter box. Verify that the voltage reading is the same, while placing the test lead probe on the end of the stud and
then on the flange portion of the ground bar. Now, repeat this for the grounding bar on the driver side, just behind the air filter box, as
well as the ground stud located on the inner side of the ECU compartment housing. By checking all of these ground connections, you will
be verifying they are all at the same ground potential. This equality in ground potential, is extremely important for all systems to function
properly. See the attached picture below for one of the three ground terminal bar connectors.

For the supply path that runs between the fuse and pin 1 at the fan connector (third component) , make a ten (10) foot test wire lead with
12 gauge stranded wire and an alligator clip soldered onto each end. One to attach to DVOM positive lead and the other will connect to the
positive terminal of the battery. The voltage potential at fuse 75 and at the battery should be at precisely the same value but it should still
be tested, so place the DVOM negative test lead onto fuse 75. If it reads more than 0.0 volts DC, record the value and then subtract it from
the reading you get when you check the voltage drop at fan connector, pin 1. This method will be much simpler than fabricating an inline
fuse holder, along with soldered pins that would then be substituted for fuse 75.

It sounds more complex than it really is, however, after these tests are accomplished, you will know for certain if all of the wiring for the
supply and ground paths are perfectly sound. Good luck in getting it all sorted out.

Regards,
Alan
 

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Alan : You da man !
 
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The M5 uses a PWM controlled fan, it has 3 wires to it, +12V, ground, and PWM signal. +12V is constant, even with the key off. The temp sensor in the lower radiator hose is a SENSOR, not a SWITCH. Never ever ever ever ever ever ever apply a voltage to a sensor connector....ever. The ECU reads this temp sensor, and sends a PWM signal according to the temp, I'm not sure what the trigger temp is though.

A blown fan is very common for our cars, a replacement fan is ~$170 off ebay, you can search the forum for what other people have bought.
 

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I tested the auxiliary fan plug for power with a test light and two of the 3 wires showed power. One of the power wires was quite dim on test light, while other one was bright. Is this normal that the two wires with power have differentiating voltages/outputs?
 

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Discussion Starter · #13 ·
yes the power is different. The two big wires are the power. The smaller in diameter wire is the feed from the DME its voltage changes depending on the speed of the fan. Don't remember but I think the faster the fan speed the lower volts. It is also pulsed volts. If you go back up in the thread I linked to another thread where the guy did some readings. It was well explained by him.

If you are diagnosing and have good power on the two big wires and volts on the small wire it is your fan unit.
This is what I found when I got mine apart.

Auto part Headlamp


Auto part Automotive tire Tire Electronics Technology


Auto part Steering part Wheel Rim Automotive wheel system
 

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I tested the auxiliary fan plug for power with a test light and two of the 3 wires showed power. One of the power wires was quite dim on test light, while other one was bright. Is this normal that the two wires with power have differentiating voltages/outputs?
Yes, reading above it seems to indicate the one 'dim wire' is actually a Pulse Width Modulated CONTROL SIGNAL from the DME that sets the fan to various speeds....
 

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That means the fan is bad.
I also happen to buy the Aux fan w/ 4 wires not 3. Blah. With the front off yesterday, was forced to put the whole thing back together without fixing the aux fan.

Yes, reading above it seems to indicate the one 'dim wire' is actually a Pulse Width Modulated CONTROL SIGNAL from the DME that sets the fan to various speeds....
 

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the best thing you can do when ordering a new aux fan is count the blades on the schroud.
10 blade schroud is a aux fan with 3 wire connection, 9 blade aux fan is 4 wire connection.

thats the fastest way to check before you order or start working on the front end.
 

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I replaced my AUX pusher fan with a Depo unit 2 summers ago. Last night the fan wont turn off. Had to disconnect the battery to keep it from running on full speed and running down the battery. I assume I just need to replace the fan again.

Has anybody else had their fan do this? :dunno:

I'll be getting a OEM fan from the dealership this time.
 

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Discussion Starter · #18 ·
Two big wires and one small wire at the plug in front of the rad. Check and see if you have volts in the small wire. If you do it is not the fan. There are reasons that the fan may run after the car is shut down. I would expect those reasons to all be gone after a few minutes. But if there is volts to the small wire you could have some other fault in the engine or quite possibly you may need your A/C system looked at. Often when an A/C system has over charge on the high pressure side the fan will run as a safety to prevent the system from getting more over charged. It is worth a check before you replace the fan.
 

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Ok, thanks. I will check that out. I cannot imagine what would cause the fan to come on after the battery has been unplugged for 2 days.

I am surprised that the power wire in the plug would stay hot with the key off.

On another note, I got the dealer to price match an online vendor. $370 is a lot better than his first quote for the fan.
 
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