the old and new fan systems
this is the old fan test routine .....not yours though .....just academic
this is good way of testing the later system on the fan logic/power etc if you only have a meter that reads frequency etc and not a scope type meter.....also some good tips on the testing of the fan at the fan itself....you can disregard he has two fans and simply follow the logic on testing the one with computer logic for the X....post number one below
I'm posting this because I searched every thread I could find on the subject of trying to figure out which component is the problem when your electric fan isn't working and there seemed to be a lack of information or what information was there was not correct.
I discovered my electric fan was not working on my 2000 328i (Manual). I wanted to test which part of the system wasn't working before I dropped $300 on a new fan. Here is what I found:
One main thing to point out is the Manual version of the car has a single electric fan on the engine side of the radiator. The automatic has an electric fan on the grill side of the radiator plus a mechanic belt driven fan on the front of the motor. The one on the grill side should be nearly identical in troubleshooting to the electric fan on the manual.
The fan is controlled by the computer (DME). The plug that goes into it has 3 wires (this is the plug on the left side when standing in front of the car facing the fan, the device mounted to the top of the fan is an air particle sensor and has no bearing on the cooling system). The two large wires are for power and ground, they are always live even when the car is off. They are hooked to the 50 AMP fuse in the glove box #36. The third wire is to control the fan speed and comes directly from the DME, there is no other fuse or relay in between. This wire carries a Pulse Width Modulation (PWM) signal.
The wires from this connector run to a box on the engine side of the fan (which the manual calls an "output final stage") and two wires go from there to the fan motor.
The car is supposed to run the fan for 20 seconds when you first turn the car on, then check to see if it is spinning, if the fan is not spinning the computer should set a code. I had no codes set on mine though.
The fan is almost always on at some speed if you have the A/C on, so perform tests with the A/C running.
The inputs the computer uses to decide how fast to spin the fan are:
Radiator outlet temperature
Catalyst temperature (calculated
A/C pressure (calculated pressure)
check computer for any set codes
unplug the fan connector and test for voltage on the two large wires.
If there is no power check the fuse in the glove box
If you have an oscilloscope you can use that to easily determine if you have a PWM signal on the wire from the DME, if not continue reading
Measure voltage from PWM wire to ground
I assumed my multimeter would give me the average voltage from a PWM signal but apparently not. I measured about .03 volts almost always when the car and A/C were on. I'll let the electronics buffs tell me why my assumption was incorrect.
If your multimeter has a frequency option test the frequency on the PWM wire.
On mine I measured 190hz during the first 20 seconds and 240hz after that. Many posts have said the correct range is 10-100hz, but unless my multimeter is very far off that is not the case
If readings on all those are ok then it's either the output final stage or the fan motor itself. You can check the motor by pulling out the fan and applying 12V directly to the motor (there is a small square plastic cap in the middle of the fan you can pop off for easy access).
In my case the motor would spin when powered so I figured it had to be the "output final stage". Unfortunately they don't sell just that part, you have to buy the whole fan, final stage, and shroud as a unit. (P/N 17117561757)
Note: I should point out that since my car was not setting codes when the fan didn't work I can't guarantee the computer will continue sending a PWM signal after the initial 20 seconds.
Last edited by devlspawn; 07-02-2012 at 04:15 AM.
devlspawn is offline