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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Tue, Jun-11-2019, 04:24:15 AM   #1
mbcm3nj
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Default Blower motor stuck on after FSR replacement

Replaced my FSR this weekend because it had been causing the fan to blow intermittently and weak upon start up. I used a Hella unit #64116923204, probably should have gone OEM. I started the car after install to see if the new unit fixed the problem and it did. The blower responded to the controls and was strong, and shut off when I turned off the ignition.

Next morning, I went to drive the car and when I turned on the air it pinned at max speed no matter what the settings read. If I shut off the hvac, I still heard the blower going and could feel air coming through the vents. When I turned the car off it continued as well. I pulled the blower fuse so it wouldn't kill my battery.

Could this replacement FSR have really broken in a day, did I create a short by accident? Super frustrating after spending 2 hours under the footwell.
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Old Tue, Jun-11-2019, 07:07:50 AM   #2
sapote
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Default Re: Blower motor stuck on after FSR replacement

The FSR is a linear motor driver which generates lots of heat as opposed to PWM driver which generates almost no heat. 99% motor drivers are PWM, and so why BMW used Linear driver is a mystery. My guess is that they wanted to minimize electrical noise — PWM voltage generates lots of wide spectrum noise - near the serial data buses under the dash.

A run away FSR can be so hot and cause a fire, so removing the fuse is the right move.

Double check the connection and if no luck, then it seems to be a bad FSR.

Last edited by sapote; Tue, Jun-11-2019 at 07:12:00 AM.
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Old Tue, Jun-11-2019, 04:57:40 PM   #3
Drewster
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Default Re: Blower motor stuck on after FSR replacement

Quote:
Originally Posted by mbcm3nj View Post
Could this replacement FSR have really broken in a day, did I create a short by accident? Super frustrating after spending 2 hours under the footwell.
Anything can happen - before diving into the dash it might also help to use INPA/ similar diagnostics to see if it can verify that lone component is at fault. If there are loads of codes on different modules, it may be something more generic like a ground issue that happens to be taking out FSR's
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Discussing Blower motor stuck on after FSR replacement in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)