1999 323i Aux Fan Issue - Technical answers needed

[GearheadNY]

I have been trying to avoid this,but I have exhausted my not making a new thread options. I have found several threads pertaining to failed aux fans on the E46 323i manual trans vehicles, but none have any pertinant information in them besides, "replace this and replace that." I was dumb enough to purchase a new aux fan, but pulled my head from my ass when i realized there was another potential issue before I installed it.

The Heart of the issue:1999 BMW 323i 5-Speed Manual

I have a new Aux Fan unit which does not fix the problem of the fan not turning on. I have checked over the normal culprits i.e. the WP the T-stat, but these are working accordingly. I do have power and ground to the aux fan, but what i really want to know is:

-What is the Aux fan signal wire signal supposed to look like (in hz or volts - have read spec is between 10-100hz)
-What is the proper test procedure for the coolant temp sensor located in the lower radiator hose. (cannot find resistance/operation information)
-What is the possibility that the Engine Computer is to blame
-If the coolant temp sensor is in fact bad will it prevent the fan from working at all even if the A/C is turned on.

As it sits right now I have good power and good ground, but no fan regardless of the A/C on or if the coolant temp rises above "acceptable" (approx 230 deg F). The fan will also not turn on to run it's preliminary fan test. The radiator is also in good shape and flows well. I will note that the vehicle will cool off once you are moving (even slowly) or if you rig the aux fan to stay on permanantly.

Any insight would be greatly appreciated! Thank you in advance!

[danewilson77]

Bump////

[Hornung418]

If I'm reading this correctly, you've purchased a replacement and installed it correctly, but it doesn't work.
My best guess would in fact be the temp sensor as you've anticipated.

[sidct]

This info is from E46 Manual:
Cooling fan in manual trnsmission is a single multispeed colling fan controlled by the DME control module via the output final stage. Output final stage is mounted on the fan housing, next to the fan motor.The fan is operated using pulse width modukated (PWM) signal and is protected by 50 amp fuse. Electric fan activation is based on the following inputs to the ECM:
-Radiator outlet Temperature
-Catalyst Temperature ( calculated Temp)
-Vehicle Speed
-Battery Voltage
-A/C pressure ( calculated pressure )
When vehicle is first started, the ECM ECM activates the fan breifly at 20% of max speed' then switches it off.This is for diagnostic monitoring. The voltage generated by the fan when it slows down ( acting as a generator) must match the stored RPM values in the fan output stage to confirm that fan is operating correctly.
Note:
if the ECM stored a cooling fan fault ' check that fan is not seized.
when AC is switched on the fan is not immediately turned on
after engine is turned off the fan may continue to run at varying speed for upto 10 minutes based on the calculated catalyst temp.

goodluck

[bmwdave37]

Did you just replace the fan motor itself, or the entire fan assembly with a new assembly?

And by new, do you mean a new oem quality part, or a new to you used part, or a new cheapo ebay part?

If you just replaced the fan motor itself, the issue probably lies in the motor resistor that powers the motor. On these fans, this is what usually fails, in my experience.

[ldinnc]

I've got almost the identical problem. The fan never cuts on regarless of AC operation or coolant temp.

My mechanic discovered the fan problem after I had the car towed to him due to evap tank rupture. He claimed the fan was bad and wouldn't operate even if voltage directly applied. He offered to replace it for $400, no labor charge but I didn't accept his offer. I wasn't convinced the fan is bad. I pulled the fan out and applied 12v directly to the fan terminals (output of fan control unit which is mounted on the fan) and the fan ran fine. Also I discovered it runs a preliminary test when engine is first started. Thus I highly confident the fan and fan control unit is fine. I suspect the radiator outlet temp sensor and will replace it today. I'm hoping that solves the problem and it isn't the ECM itself. Btw, I'm getting ohm readings from the temp sensor of 7 - 10 ohms and I read 5v across the open terminals of the temp sensor wire from the ECM. Anyone know if those are correct values?

I'll post my findings after replacing the temp sensor.

[ldinnc]

UPDATE

I replaced the radiator outlet temp sensor but that did not correct the problem. The fan starts and runs when engine is first started but then doesn't cut on due to high coolant temp. Also, AC cuts out, I'm guessing due to high pressure due to fan not running when it should. I believe the AC cutting out is a result of the fan not running rather than causing the fan not to run.

I just drove the car for 10 mins. and let idle for about 5 additional mins., all without the AC running. The fan seemed to operate fine. Temp guage stayed dead center and fan was running. I then cut on the AC while the car was idling. It was blowing cool air for a short while, then I heard a hissing sound and the air turned warm. I continued to let it run and soon the temp guage started moving toward hot. I checked and the fan was not running. I turned off the AC but the guage continued moving toward hot so I cut off the engine. I'm now wondering if the AC is somehow causing the fan to not operate.

Anyone have any suggestions or know how I can further troubleshoot?

[rx7world]

I don't think anybody has answered the questions, I have the same problem, tried new oem aux fan still fan does not come on under any circumstance. Here is the original question.

I have a new Aux Fan unit which does not fix the problem of the fan not turning on. I have checked over the normal culprits i.e. the WP the T-stat, but these are working accordingly. I do have power and ground to the aux fan, but what i really want to know is:

-What is the Aux fan signal wire signal supposed to look like (in hz or volts - have read spec is between 10-100hz)
-What is the proper test procedure for the coolant temp sensor located in the lower radiator hose. (cannot find resistance/operation information)
-What is the possibility that the Engine Computer is to blame
-If the coolant temp sensor is in fact bad will it prevent the fan from working at all even if the A/C is turned on.

As it sits right now I have good power and good ground, but no fan regardless of the A/C on or if the coolant temp rises above "acceptable" (approx 230 deg F). The fan will also not turn on to run it's preliminary fan test. The radiator is also in good shape and flows well. I will note that the vehicle will cool off once you are moving (even slowly) or if you rig the aux fan to stay on permanently.

[rx7world]

Don't have answers to the above questions but did fix it, it was to simple.

[NDubSki]

Check fuse 50. That's all it took for me

[billy mitchell]

Don't have answers to the above questions but did fix it, it was to simple.

I seem to have same type of problem but my car is 323i auto ..I can get fan to work using INPA and after doing a AUX fan test the A/C runs ok for a day ...seems that if in stop start traffic the A/C does the same ..if I give the motor a rev it gets A/C working ..am thinking if I replace the pressure switch and dryer and expansion valve this would just leave the coolant temp sender the last thing to replace but the temp gauge sits in the center of the gauge ...so what was your fix ?????

[Muzz258]

Have you pulled the connector off the coolant temp sender and shorted the connection to force the fan to start? If it starts, then its the sender, if not then you have fan problem.

[MarcoZandrini]

Read this: https://drive.google.com/file/d/1Cac...BTPQDJx6u/view. Then scan the engine computer (DME) for codes. The SES light is on only when an emissions related code is present.