This message is marked as Important.

Subject: Troubleshoot Auxiliary Cooling Fan - Component checklist and notes Author: davidsoine : member since September, 2004 : 996 posts Posted on: 2007-08-22 00:55:59

For e38s made from 9/95 to 9/98, I put together a simple checklist for the auxiliary cooling fan circuits.

Aux Cooling Fan Component Checklist

There are 3 individual circuits that control the cooling fan speed (low/mid/high), referred to as Stage 1, Stage 2 and Stage 3.

Additional troubleshooting notes:

0. As has been stated before, the aux fan should turn on (low speed) immediately when the A/C compressor cycles on.

1. Resistors: Use the information on e38.org or search this forum for how to troubleshoot the resistors.

2. CHECK THE FUSES!

3. The Fan/Resistors connector can be accessed without removing the bumper. Just reach in between the bumper and air duct, rotate the connector counter clockwise, and carefully pull the connector and wiring out. If you have Giant Hands, get someone with small/thin hands to help you out.


Some of the wiring in the harness had cracked insulation...note the liquid electrical tape:


4. An easy way to check the fan and resistors is to pull the connector apart, ground pin 1 (brown wire) and apply 12-14 volts to the other 3 pins individually (use a fused test lead, etc). The fan should turn on when voltage is applied to pin 2,3 & 4, and you will notice that the speeds are different depending on the pin.

5. Stage 1 (low) and Stage 3 (highest speed) circuits can be tested by pulling off the connector at the Dual Temperature Switch:


6. Pull the connector to the Dual Temperature Switch. The airbox can be moved aside to gain access. There are 3 pin sockets on the connector, the "middle" pin socket #2 goes to ground..check that it does. Shorting pin 1 & 2 will (key on) will turn on the Stage 3 circuit and the fan should blow at high speed. Shorting pin sockets 2 & 3 will turn on stage 1 (low fan speed). If the fan doesn't turn on, check the fuses & Relay for the respective circuit.

7. Relays: They are behind the glove box:


8. Relays: K21 (low speed), K22 (mid-speed), and K201 (high speed) can be pulled out and checked: Ground 85, apply 12-14 V to 86, and
the switch will close between the other 2 pins.


9. Coolant temperature at the Dual Temp Switch is not the same as the temp at the water pump housing...so don't worry that the fan doesn't turn on when the coolant temp shown by the cluster hits 91 or 104 degrees. Temperature at the radiator is lower. "BMW635" notes that his aux fan turns on low at a reading of 107-110 deg, and high around 117 deg (this would be without A/C on). It may be hard to hit those temps while troubleshooting in the garage.


Whew. Hope that helps.

best,

Dave
97 740iL 218k Miles

• Troubleshoot Auxiliary Cooling Fan - Component checklist and notes (pic) (url) - davidsoine 2007-08-22 00:55:59 (21025 views)
  • Re: Troubleshoot Auxiliary Cooling Fan - Component checklist and notes - robertwayne7159 2011-07-31 07:10:13 (205 views)
  • Re: Troubleshoot Auxiliary Cooling Fan - Component checklist and notes - mroney 2011-07-21 20:56:21 (186 views)
    • Re: Troubleshoot Auxiliary Cooling Fan - Component checklist and notes - bofett 2012-02-19 01:36:52 (25 views)
    • Re: Troubleshoot Auxiliary Cooling Fan - Component checklist and notes - bofett 2012-02-19 01:31:22 (27 views)
  • Re: Troubleshoot Auxiliary Cooling Fan - Component checklist and notes - rescue28 2011-06-28 21:33:41 (192 views)
  • Re: Troubleshoot Auxiliary Cooling Fan - Component checklist and notes - gilmotl1 2010-09-12 00:20:33 (375 views)
    • Re: Troubleshoot Auxiliary Cooling Fan - Component checklist and notes - gilmotl1 2010-09-12 21:50:38 (315 views)
  • Nice work, David! Definite e38.org material. (nt) - DavidC 2007-08-22 04:23:47 (625 views)
  • Thanks for this, I plan to use your info.... - bugs1357 2007-08-22 03:03:52 (629 views)
  • Another MO ox green?!! (nt) - Ed 2007-08-22 01:08:34 (545 views)
  • FYI this should be good for M62 & M73, 9/95 to 9/98 build dates. (nt) - davidsoine 2007-08-22 01:05:26 (734 views)