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2001 SLS, Engine overheats unless the a/c is on.


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Hello everyone,

My 2001 seville SLS overheats unless my a/c is on max. It all started when I notice my fans were not turning on, which made my car overheat. I changed out the coolant

temp.sensor and that got my fans running again. But when I drive at high speeds (High Way) or when I sit in traffic or at a drive-thru window the temp starts climbing untill I begin

to move again and the temp goes right back to normal. Now if my a/c is on my car will not overheat at all. Now the other day I notice that when my a/c is off my fans never switch to

high they only run on low no matter the engine temp, but as soon as i turn my a/c on the fans kick into high and keep my engine cool. Why wont my fans go into high unless the a/c is

on?

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Well, it's always a good idea to start with posting your DTCs (Diagnostic Trouble Codes) here. If you don't know how to do that, have a look here:

http://myweb.accessu...idiag.html#2000

Your fans should operate at LOW speed when your coolant temperature reaches 223 degrees. At 234 degrees, they should switch to HIGH speed. As you know, they are on all the time if the A/C is operating.

Three relays in the underhood fuse compartment control the fan speed in response to commands from the PCM or Powertrain Control Module.

Since your fans can run at HIGH or LOW speed it looks like the motors, the fuses, the relays, and their connection all the way back to the PCM can be considered good. It would appear your PCM doesn't "know" the water temperature has exceeded 223 degrees and the fans should be turned on.

Any chance the coolant temperature sensor you installed might be bad or have a poor electrical connection? Is it an OEM sensor?

Oh, and . . .

:welcomesmiley:

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There is no means of avoiding the final collapse of a boom brought about by credit expansion. The alternative is only whether the crisis should come sooner as the result of a voluntary abandonment of further credit expansion, or later as a final and total catastrophe of the currency system involved. - Ludwig von Mises

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:welcomesmiley:

We do need the codes, but it sounds like you have a bad connection on either the fans or one of the fan relays, or that one of the fan relays is bad. The fan relays are the three boxes on the bottom of the bracket that holds the three fans.

The fans should always be on low speed when the A/C is on. This provides a simple way to turn them on at low speed so that you can troubleshoot the problem.

I would start by looking at where the wiring harness plugs into the relays and the fans, and make sure that the connectors are all clean and tight.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Thanks for the quick response guys, When I went to check the DTC's it asked me, ALL?, VTD?, TTM?, PCM?, IRC?, DIM?, OR DIC? so I just selected "ALL" it then started giving me a bunch of codes the first series was MSM B1735, B1740, B1745, B1750, and so on until B2355 then it started giving me U1000, U1064, U1016 then it agve me PCM P0335 and P0386 and finally it gave me D0410current. What I'm going to do now is change the fan relays. Are all of the relays in the fuse and relay box under the hood? Today I realized that when I'm on the highway my fans turn off and when I get to a stop light thats when my car starts to overheat. If I turn off and turn back on the a/c the fans will turn on until I get to high speeds again and then it starts to overheat again...

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Hows it running?

P0335 - CKP Sensor A Circuit Performance

P0386 - Crankshaft Position (CKP) Sensor B Performance

Changing the fan relays would be a waste of money, that is not needed at this point you dont have any cooling fan codes

This may not be a cooling fan problem, with the AC off, the cooling fans wont come on till 228 degrees and they will turn off at 217 degrees, you will see wide ranges of temps with the AC off.

You need to make sure you have proper coolant levels, you need to make sure you dont have AIR in your system check the purge line, you need to make sure your cooling system holds pressure check the cap, it must be at least a 50/50 mix of coolant to water and you MUST make sure your thermostat is good, and check the water pump belt. IF your fans turn on at 228 and turn off at 217 they run correctly, IF you turn your AC on and they run they are running correctly.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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And, you need to change your crankshaft sensors before you start having stalling and no-start problems.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Are all of the relays in the fuse and relay box under the hood?

Yes.

2001_Seville_Fans2.gif

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There is no means of avoiding the final collapse of a boom brought about by credit expansion. The alternative is only whether the crisis should come sooner as the result of a voluntary abandonment of further credit expansion, or later as a final and total catastrophe of the currency system involved. - Ludwig von Mises

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