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I have and 05 STS 3.6 with 169K Miles. Sufficed to say the car was not well maintained by the previous owner. Bought it a few weeks ago at auction. Had a Bad Floor shifter and the Cooling Fans were pretty much burnt up with the motors falling out the assembly. Replaced the Cooling Fan Assembly with a used part. Worked at the repair shop for a day of two then one of the motors seized up. Junkyard gave me a working replacement. Installed the replacement assembly and the fans won't kick on when the car gets up to temp and subsequently the car gets warm and starts to overheat.

Things we have Checked-Fans will not kick on even when running the A/C. Fans WILL turn on when jumped from the relay. Unplugged the Coolant Temp Sensor...no change. Changed the Thermostat...no change. Swapped the coolant fan relay...no change. Checked the water pump, Coolant seems to be circulating properly. Looked for signs of bad/worn wiring in the Coolant Fan harness.

What are we(myself and the mechanic) missing? Do the Coolant Fans in the 05 + STS have a module? If so, does anyone know the part#? Could the first junkyard coolant fan assembly that seized up, possibly have fried the module or a computer? Please remember the fans that came with the car were sooooo bad, that the wiring was fried and the motors had actually fallen out the back of the fan assembly.

My next step is to run the codes and look for anything relating to the fans. If that doesn't yield anything, send it to a Cadillac Repair shop to pinpoint the issue. Anymore tests that I can run or step by step diagnosing I can do before I send it to the pros?? Could this be a more serious electrical issue? Any help you guys can lend is greatly appreciated. I did some reading, not much out here with the 05 + STS relating to the cooling fans. My general mechanic is stumped.

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Do you mean that you pulled the relay and jumped it with wire(s)? If so, why don't you replace the relay. Maybe the relay is not working?

There are three (3) relays for the system: 1) Low speed; 2) Hight speed; and 3) S/P (sustained power?) I believe you will find all of them in the engine compartment fuse block on the passenger side.

The ground for cooling fans is G104 and is located on the passenger side, bottom, near the fog/turn signal lights, to the right about 1-foot if you're standing in front facing windshield.

At any rate, the best way to find problems is to first scan for codes.

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12 hours ago, Grahamzach said:

I have a 2005 cts with the same issue, could you PLEASE tell me what solved your issue I've tried everything you have tried and I'm lost. Thank you in advance!

Have you checked for codes?


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

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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I just took it yesterday to get the check engine light code ran and it said bank 2 sensor 2 o2 electrial curcuit had no activity detected, but that has nothing to do with the cooling fans not coming on. I'm not sure what to check next. Any ideas would be greatly appreciated.

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Explain what you mean above when you say "Fans WILL turn on when jumped from the relay"

Explain EXACTLY how you did that


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

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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