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1998 Cadillac STS
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Discussion Starter #1
Sorry to post this again but for some reason I can't find someones response on this subject awhile back. Well, I located the odd sound coming from under my dash near the parking brake. It was mentioned on certain STS's, the dealer put a small fan to move air over the HVAC sensor by the driver side vent. Is this the culprit on my dashboard (see image)? When the sound (flutter) comes on, this piece vibrates. Thanks Dave D.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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18,855 Posts
Re: '98 Cadillac Seville STS Dash Sound

Sorry to post this again but for some reason I can't find someones response on this subject awhile back. Well, I located the odd sound coming from under my dash near the parking brake. It was mentioned on certain STS's, the dealer put a small fan to move air over the HVAC sensor by the driver side vent. Is this the culprit on my dashboard (see image)? When the sound (flutter) comes on, this piece vibrates. Thanks Dave D.
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behind that grill is the cabin temperature sensor -

It was mentioned on certain STS's,
the dealer put a small fan to move air over the HVAC sensor by the driver side vent.

actually - that component is on EVERY Seville - and on EVERY Cadillac with automatic climate control -
without it - the automatic climate control system wouldn't know the cabin temp -

ACDelco 15-51153


the snorkel fits tight to the back of the grill -
there is a tiny thermistor - a temp sensor - in the snorkel -
the larger square section holds a tiny "muffin fan" - like whats inside a computer -

two things typically affect these sensors -
dirt/dust/hair/etc actually coat the thermister - thus insulating it -
the symptom is usually uneven cabin temp -

the other issue is that the fan bearing gets dried out and the fan makes goofy noises -
this usually happens the first really cold morning in the winter -

some have had luck pulling back/removing the small round label covering the center of the fan motor -
and deploying a small drop of a VERY thin oil - like Marvel Mystery Oil -
then sticking the label back on -

others just decide to replace the sensor -
 

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1998 Cadillac STS
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Discussion Starter #3
Re: '98 Cadillac Seville STS Dash Sound

Thanks, any ideas on the best way to get to it? I notice the panel directly under the steering wheel with an air duct is some what loose. Dave D.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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18,855 Posts
Re: '98 Cadillac Seville STS Dash Sound

Thanks, any ideas on the best way to get to it? I notice the panel directly under the steering wheel with an air duct is some what loose. Dave D.
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access is by removing the trap door on the side of the cluster -

with all the stuff you are doing - and WILL be doing -
you REALLY NEED the FSM - Factory Service Manual - it is a 3-volume set -
and I found a great deal for you - $17.55 - for all 3 volumes - including shipping -

https://www.ebay.com/itm/1998-Cadillac-Chevy-GMC-Buick-K-Platform-Seville-OEM-Service-Manual-Volume-1-3/183660693202?hash=item2ac307c6d2:g:iV4AAOSw~VBcUQgg/361355912231?hash=item54227da427:g:UToAAOSwgQ9Vv7vt
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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It's not a "dealer install" - in one form or another the cabin air temp sensor is part of the HVAC system in every one of these cars.

Open the driver's door, stick your index finger into the black rubber air duct opening for the window - in the end of the dash - yank the end of the dash off. Remove the small plastic duct. Straight inside you'll see a small hex head machine screw - loosen it, remove it with mechanic's fingers. Snake out and disconnect the electrical connector, remove the module, open it and blow it clean with computer air. Uncover the muffin fan center axle and place a drop of 5W-30 synthetic oil on the axle and re-cover it. Install the module. Reassemble the rest.

https://www.google.com/search?source=hp&ei=Vp7xXPebAoWvggff4YbwAQ&q=cadillac+forums+seville+deville+eldorado+cabin+air+temperaure+sensor&oq=cadillac+forums+seville+deville+eldorado+cabin+air+temperaure+sensor&gs_l=psy-ab.12...1378.20381..26000...0.0..0.242.7984.12j55j1......0....1..gws-wiz.....0..0i131j0j0i22i30j33i22i29i30j33i299j33i160j33i10.CfOgH6dK1hM
 

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1998 Cadillac STS
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Discussion Starter #6
Thanks to both you guys. Your illustration is very helpful Submariner409. Now, I think I got this one. But YES Basscat, maybe I should get my hands on those manuals. I can see where they will be very helpful not only on this project but other down the road. Will take a shot at this weekend.
 

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1998 Cadillac STS
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Discussion Starter #7
I successfully removed and lubricated the fan. Now, I want to check to see if the fan is operational. Question: is the fan always on if the HVAC system is on? Or does it come on intermittently? While doing the removal the front grill came off. I am thinking of taking it off again so I can see if the fan is working properly. Another concern is that after I lubricated the fan which I have done before with computer case fans, I manually rotated it several times to get the lubricant down inside. For some reason, it did not freely spin alot. It went around maybe one or two times. As I remember, freely spinning these fans after lubrication, they will go for quite some time. On a side note: the sensor was dirty but not so much the fan. And I order the Factory Service Manual but they have not arrived.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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18,855 Posts
I successfully removed and lubricated the fan. Now, I want to check to see if the fan is operational. Question: is the fan always on if the HVAC system is on? Or does it come on intermittently? While doing the removal the front grill came off. I am thinking of taking it off again so I can see if the fan is working properly. Another concern is that after I lubricated the fan which I have done before with computer case fans, I manually rotated it several times to get the lubricant down inside. For some reason, it did not freely spin alot. It went around maybe one or two times. As I remember, freely spinning these fans after lubrication, they will go for quite some time. On a side note: the sensor was dirty but not so much the fan. And I order the Factory Service Manual but they have not arrived.
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is the fan always on if the HVAC system is on?
the fan is always ON -

I am thinking of taking it off again so I can see if the fan is working properly.
removing the grill will also allow you to help line it up properly -

For some reason, it did not freely spin alot. It went around maybe one or two times.
these are tiny brushless motors - they don't just spin freely -

I order the Factory Service Manual but they have not arrived.
you'll be ready for ANYTHING that comes up in the future -
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Yup ^^^ to all.

The brushless muffin fan uses permanent magnets - it will act - if spun - like there are soft-acting gear teeth in there.

Once a year, remove the little grille and carefully blow out the tunnel/sensor with canned "computer air".
 

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White Diamond '03 DHS (with DTS floor shift)
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Other thatn the blower motor, that's the only one I can think of off hand.

P.S.
It's possible that the fan bushings are simply worn and lube may not help.
 

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14 SRX, 00 SLS, 99 Deville 50-year Anniversary
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You can put your ear right next to the grille you'll hear the faint white noise of the fan running with key ON.

I remember mine was also making that noise when I got the car. One drop of 5w30 and it was quiet for 10 years.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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Okay, BTW are there other sensor/fans I should clean up? Thanks Dave D.
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technically -
there are 4more temp sensors built into the ducts -
but I have never heard of them malfunctioning -
and the cabin air filter should keep them clean -
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Discussion Starter #16
Thanks everyone, we are good to go. The fan is working properly now without any noise. Dave D.
 
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