E30 Aux Fan
Resistor Replacement (Bosch)

Prepared by VietSB
Modified 06.29.02

NOTE: Perform these steps at your own risk. All P/N's listed are a "best guess", so please double-check with your local dealer. These mods and repairs were performed on my US-Spec 1989 325i (12/88 prod date, M20/B25 engine) but there is no guarantee they will work on other E30's. These instructions are provided for entertainment purposes only!

NOTE: The aux fan can run anytime the key is in the ignition, so use extreme caution!

THE GOAL: Replace the ceramic resistor to resume low-speed aux fan operation when the A/C is turned-on.

I checked the fuses and they were okay. Testing at the radiator temp switch plug, I found that high-speed setting worked fine, but I only heard a relay click instead of low-speed fan operation. An inspection under the car revealed that the low-speed Bosch ceramic resistor had cracked in half (see pics below). These instructions do not cover troubleshooting issues with the radiator thermo switch or A/C-on signal wiring.

Required Tools and Parts:

There are two different resistors listed for E30's, the Bosch (ceramic) and the Magna (plastic-encased?). These instructions are for the Bosch resistor pictured below (on the right).

1. Remove the front license plate (if present) and remove the (2) mounting screws holding the resistor bracket to the aux fan assembly.

2. Turn the resistor around and make note of the wiring layout. Unscrew both wire terminals at the ends of the resistor and replace with the new resistor in the same fashion. Getting the wires re-attached is probably the most difficult part due to the cramped work space. Attach the resistor bracket, check that all wires are clear of the aux fan, and test for functionality when the A/C is turned-on.

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