I don't have any help for testing it, but I can tell you that it is not a switch. It is a temperature sensor. The fan is not only on or off like some cars, it is variable speed depending on the return coolant temperature and the AC high side pressure.

 

You could try searching as there is a lot of data on this topic:

BMW-North E46 Electric Fan Guide

Here's a post from a few days ago:

You likely want to verify that the electric fan is functioning correctly as part of the diagnosis. INPA is a BMW diagnostic tool - you might not have that but it's the best for delving into fan issues.

Often a bad lower rad hose outlet coolant temp sensor (CTS) can cause erratic fan operation. Worse when it puts out plausible but false readings (I.e. too low).

The CTS is a cheap replacement - just be sure to use an OE genuine. I think it's Hella.

If you want to try to see if the fan is operational and you don't have INPA to test try this:

1. Have car engine OFF
2. Unplug the lower rad hose coolant temp sensor
3. Start car (preferably not while engine coolant is too HOT i.e. above 95C) let idle 15 secs then turn on AC compressor.
4. Fan should start spinning on high speed within 30 secs - If not shut car OFF to avoid overheat.

This test only tells you that the fan motor works. It does not imply that the CTS is operationally functional, nor that DME and/or the fan module are processing correctly.

The problem at this juncture could be anything from a bad CTS, cut wire, blown fuse, unplugged fan, or the most common issue - a failed fan control module (bolted on the shroud) - usually corroded terminals but often failed internal components.



There is a thread on here which tells you how to display the engine coolant temp on the cluster - Search for "hidden OBC functions" - you will want to display the actual coolant temp during these tests. Remember that the temp displayed is from the Engine Coolant Temp sensor (ECT) not the CTS.

Once you rule out the fan and/or CTS as bad then you can see if the AC operates. I doubt the DME is bad, sounds like it is doing it's job (shutting off AC to protect engine temps)

You could measure the resistance value difference between the CTS at cold engine and at op-temp engine (92-95C) The difference should be greater than 200 ohms. If not the CTS is shot.

 

You could try searching as there is a lot of data on this topic:

BMW-North E46 Electric Fan Guide

Here's a post from a few days ago:
You likely want to verify that the electric fan is functioning correctly as part of the diagnosis. INPA is a BMW diagnostic tool - you might not have that but it's the best for delving into fan issues.

Often a bad lower rad hose outlet coolant temp sensor (CTS) can cause erratic fan operation. Worse when it puts out plausible but false readings (I.e. too low).

The CTS is a cheap replacement - just be sure to use an OE genuine. I think it's Hella.

If you want to try to see if the fan is operational and you don't have INPA to test try this:

1. Have car engine OFF
2. Unplug the lower rad hose coolant temp sensor
3. Start car (preferably not while engine coolant is too HOT i.e. above 95C) let idle 15 secs then turn on AC compressor.
4. Fan should start spinning on high speed within 30 secs - If not shut car OFF to avoid overheat.

This test only tells you that the fan motor works. It does not imply that the CTS is operationally functional, nor that DME and/or the fan module are processing correctly.

The problem at this juncture could be anything from a bad CTS, cut wire, blown fuse, unplugged fan, or the most common issue - a failed fan control module (bolted on the shroud) - usually corroded terminals but often failed internal components.



There is a thread on here which tells you how to display the engine coolant temp on the cluster - Search for "hidden OBC functions" - you will want to display the actual coolant temp during these tests. Remember that the temp displayed is from the Engine Coolant Temp sensor (ECT) not the CTS.

Once you rule out the fan and/or CTS as bad then you can see if the AC operates. I doubt the DME is bad, sounds like it is doing it's job (shutting off AC to protect engine temps)


You could measure the resistance value difference between the CTS at cold engine and at op-temp engine (92-95C) The difference should be greater than 200 ohms. If not the CTS is shot.

So I'm still overheating when coming to a stop. I used your guide to test the fan speed in INPA.

Result:
-The fan doesn't work at any speed.

Prior tests:
- Fan turns on when the A/C is turned on
- A/C turns off when temp is higher than operating temp
- 12v always on at the fan connector pigtail
- Replaced bad CTS with an assumed working CTS

INPA error (in German):

125 E-Luefter
Error frequency : 1
Logistic counter: 40
N_32 736.00 rpm
MAF 103.49 mg/stk
TCO 93.00 Grad C
VB 12.95 V
aufgetreten vor (rel. BZ) 0.30 h
KS-->VB/Masse o. Leitungsbruch
---
---
---
---
Fehler entprellt
Fehler momentan vorhanden
statischer Fehler
Errorcode: 7D 61 01 28 17 13 BC 7F 91 BA
=============================================================

I think it's a bad fan module. Especially with the 125 Electric fan error.

 

Disconnect the plug. You use a wire and touch opposite pins within the sensor on the side of the radiator. You can have the car "on" but not started. The fan should spin. Otherwise, fan clutch is shot. OR better yet, and this happened to me. Water pump is on its way out any second. The tow cost me as much as the pump. Be careful.

 

Disconnect the plug. You use a wire and touch opposite pins within the sensor on the side of the radiator. You can have the car "on" but not started. The fan should spin. Otherwise, fan clutch is shot. OR better yet, and this happened to me. Water pump is on its way out any second. The tow cost me as much as the pump. Be careful.

Wait...

The fan clutch is only a part of the mechanical fan, and only the mechanical fan mounts to the water pump. The clutch is not even remotely controlled via anything electrical. Also, it's not going to start spinning unless the engine is running.

The OP certainly seems to be talking about the electrical fan, either the aux fan or the main fan (if a manual transmission).

 

Yea I'm referring to the fan that connects to the pump. The switch on the side controls the aux fan.

 

... The switch on the side controls the aux fan.

It's not a "switch."

 

OP. Water pump is about to be SHOT. Bottom line.

 

It looks like you dont know s**t about cars. You should be banned for giving stupid comments and advices.

Water pump has nothing to do with this. As mentioned before,electric fan is stepless controlled from DME, regarding radiator return temperature and AC gas pressure.
The best way to test sensor/fan is via INPA. You can see the temperature data from the return line to see if sensor works OK. Also you can test your fan by activating it and set the % of the speed to see if it works as it should.

 

I don't think there is any point in arguing with him. It's a shame...

 

I'm not sure whether anyone can point me in the right direction, but I am hopeful. I own a 2000 BMW 323i with manual transmission. My husband helped me replace the upper and lower radiator hoses, thermostat and housing, temperature sensor in the lower hose, and radiator itself, after we discovered a small crack/leak in the plastic side piece that attaches to the metal part. The expansion tank was intact, but we did get a new cap for it, due to a small threading section missing/broken. After all of that, we refilled it with coolant and drove it around, but it was still overheating and the heat failed to work. Turns out, I failed to properly bleed the system, so I did that. Now, the temperature seems to remain steady BUT the electric fan is still not working. I checked the 50 AMP fuse (#37) in the glove box, and it looks fine. I then disconnected the fan from the thing into which it plugs and held my reader for voltage into that thing, primarily on the red wire's portion. Nothing. I believe I'm supposed to get a 12 volt reading. I did this with the car off, then with the key turned. Still nothing. I followed the wire from this connection around the front of the hood toward the passenger side and to the glove box. If anyone knows whether I'm going in the right direction and what I should try next, I would greatly appreciate it. I'm a mom/English teacher and have to return to work tomorrow, so I'm hoping to address the issue. My daughter is taking her driving test soon and is supposed to drive this car.

 

... I checked the 50 AMP fuse (#37) in the glove box, and it looks fine. ....

Looks fine, may not be enough. Did you test it? Test for voltage (fan should be plugged in for this) on both sides of the fuse. You should get battery voltage (referenced to ground) on both sides of the fuse. If it's on one side only, you know the fuse is bad. If it's on neither side, then the circuit has failed somewhere before the fuse. (Do verify that your meter is working correctly by reading battery voltage at the battery. Also always make sure you have a true and good ground connection for the negative lead.)
You can also remove the fuse and measure resistance between the two fuse terminals. (Never do this with the fuse installed.)

 

Thank you! I will try to do those things. I'm not very car savvy/electronically savvy, but I will certainly try. I really appreciate the suggestions.

 

12 volts found!

Thank you, again! I did a quick Google search on how to use the specific voltmeter I have, and I was not using it correctly at first. Once I got past that hurdle, I tested the wires and got 12 volts, so I decided to order a new electric fan. I guess it makes sense that after 16 years, some of these parts just get tired and quit. I'm extremely grateful for the helpful feedback/suggestions so that I can get this car ready for my daughter to drive. You both are very much appreciated.

 

E-lufter error 125 - the dme sent a speed request to the fan. The fan rpms are then measured (as voltage) by the fan module and reported back to dme (at this point the fan is actually a micro voltage generator) if the value reported is out of spec error 125 is recorded.

Yep fan module is toast. I just put the above description in case anyone wondered about the protocol. Either find a donor Bosch fan module or replace the assembly.

 

Overheating when you're at a stop, so fan related?

Not necessarily true. See my cooling thread stickied at the top of the forum for info on what's required to actually cool an E46 down. (or any car for that matter.)

You can have the following problems:

Blockage in the coolant (sludge, gunk, dead mice)

Blockage of air between condenser and radiator or in FRONT of condensor (leaves, bugs, horse hair)

Reduced flow due to broken impellers of water pump

Dead temp sensor

Dead fan(s)

Interruption of water chain (bubbles in coolant)

Not enough coolant

 

Why don't you just stick to shamelessly selling for FCP. The error code was in the log. The inpa test confirmed the fan failed, or do you just troll now looking for threads where you can advise folk to replace their entire cooling system with parts from your new sponsor.

 

Yeah. It's definitely a soft fail.

I was finally able to tested fan speeds via INPA.
When it was cold and all ranges worked.
Once the car got warm, the fan wouldn't respond to INPA. Car would then begin to overheat.

I just bought a Behr. Hopefully, it'll last me more than 2-3 years as other members point out.

I'm guessing the soft fail fan caused a 3 yr old Behr radiator to bow out too. Sigh.

 

Glad you found it before you lost an engine. As I have noted you could replace every single cooling component like one on this board always preaches but if you don't check this fan properly - you will start replacing them again. The soft fail as you termed it is the most difficult since owners see the fan spin sometimes and think it must be working ok. It was this very scenario that got me researching the inner workings of this fan about 6 years ago.

Not sure if you realized but you could have just changed the Bosch Fan Module with a newer one from a Mazda or Volvo or a few other makes.

Just recommended that fix for a guy in this thread:

I buy them (late model, southern states) and rebuild E46 Bosch Fan Assemblies that will outlast anything that Behr is making out of China with poor quality components and shoddy assembly. (Info on Behr e46 Fan Assembly Linked here)

I can honestly say that I have NEVER come across a Bosch Fan assembly where the motor was worn out or burned out. I posted a pic of one of my Bosch fans - removed from a 2001 e46 vert and the brushes had almost no wear on them. All the wiring is copper (unlike the Behr) and the bearings are German - you can guess where the Behr bearings are from.

Insides of both fan motors and modules are in the Electric Fan Guide here.

 

Not sure if you realized but you could have just changed the Bosch Fan Module with a newer one from a Mazda or Volvo or a few other makes.

Just recommended that fix for a guy in this thread:

I buy them (late model, southern states) and rebuild E46 Bosch Fan Assemblies that will outlast anything that Behr is making out of China with poor quality components and shoddy assembly. (Info on Behr e46 Fan Assembly Linked here)

I read your guide front to back. How do you rebuild the fan module? Are you purchasing specific parts that fail from digikey or the sort?

Yeah. I looked up the bosch fan modules for the cars you mentioned and found that I'd have to spend at least $200 or so just for a new fan and module. Maybe that would have been a better idea than buying a Behr fan.

Anyway, I'd like to rebuild mine if you have the knowledge to share.

 

Fan Man!

Ok I overheated like most e46'ers brought to this thread...

Since I had not heard the FAN kick on I bought the OBDII-USB Cable
with INPA. Grabbed an old XP laptop. Set it up, and with INPA was able to operate the FAN from 10% to 90%.

But Still like others have stated the FAN seems to only operate if I turn on the A/C...

So if INPA can operate the fan. Then stuff like the Fuse, DME, & that FAN control box I think you referred to rebuilding should all be OK?

Whats going on with these E46's cant turn on the Cooling Fan?

 

Fan Man!

Ok I overheated like most e46'ers brought to this thread...

Since I had not heard the FAN kick on I bought the OBDII-USB Cable
with INPA. Grabbed an old XP laptop. Set it up, and with INPA was able to operate the FAN from 10% to 90%.

But Still like others have stated the FAN seems to only operate if I turn on the A/C...

So if INPA can operate the fan. Then stuff like the Fuse, DME, & that FAN control box I think you referred to rebuilding should all be OK?

Whats going on with these E46's cant turn on the Cooling Fan?

Did you ever figure this one out?

 

- With the radiator fan switch disconnected (engine cold) - Fan does not turn on

What radiator fan switch? There is no such thing for this car. Are talking about the temperature sensor on the radiator bottom hose?