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Old 08-05-2011, 12:14 PM   #3
bazar01
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Quote:
Originally Posted by kaamacat View Post
Question. I am wanting to see if my fan will run both the high and low speeds with a manual override. (Checking to see if the fan is operating properly, as I've never heard it run accept when the A/C is on, which I know the HS side will kick on immediatly, and does just fine)

Car year is 1997 318ti/M44 (1/1997 build)

I've disconnected the radiator sensor plug, and can bridge the brown -> Black and get the high-speed setting to kick-in, but, when bridging the other side of the plug to brown.......I get nothing on the low-speed side. (Think it was the green stripe side)

I did this with ignition key on (engine off).

I've also seen a post mentioning that the high-speed relay (magenta in color) if bad could also cause this, where the HS side works but LS does not.

Long-story-short, how can I manually test the low speed fan?
Jess is correct. The HS relay contact is interlocked with the LS relay.
Additionally, the LS relay coil is interlocked with the ECU and the low temp contact in the radiator temp switch. This is the reason why the fan did not run when you bridged the other side of plug to the brown (ground). The ecu input is open. The LS relay coil has to be energized thru the ecu and the radiator temp switch contact. Here is the schematics. Follow the blue line for energizing the LS (low speed) relay coil. The ecu role is circled in blue. On early models, the ecu has no role in the aux fan operation
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Last edited by bazar01; 07-10-2017 at 01:44 PM.
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