Cooling fans will not turn on

Tiny
BCMULLEN95
  • MEMBER
  • 1994 BUICK LESABRE
  • 130,254 MILES
The cooling fans will not turn on. The fans do work tested while off vehicle, but when plugged into car they will not turn on. The relays both tested okay. What else should I be looking for. I tested resistance from relay to fan and it testes okay. At this point am I looking at a problem with the PCM?
Thursday, December 29th, 2011 AT 7:58 PM

44 Replies

Tiny
BCMULLEN95
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  • 249 POSTS
The a/c has been removed and has a bypass pulley, however unplugging the CTS and/ or turning on the a/c has not effect on the fans.
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Thursday, December 29th, 2011 AT 8:13 PM
Tiny
BCMULLEN95
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The fans still do not turn on.
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Thursday, December 29th, 2011 AT 8:23 PM
Tiny
JDL
  • MECHANIC
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What is litre size of engine? How hot is the engine temp reaching? Some fans won't even turn on till about 225 degrees F.
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Thursday, December 29th, 2011 AT 8:48 PM
Tiny
BCMULLEN95
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The temp was to 260 degrees, no fan turned on with or without the CTS plugged in. Is it possible the PCM has failed?
I have also noticed that the alternator is not charging the battery at idol at this point also.
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Thursday, December 29th, 2011 AT 9:10 PM
Tiny
JDL
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At this point, if the battery is down and the charging system isn't working, you can't check anything. We are just spinning our wheels.
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Thursday, December 29th, 2011 AT 9:18 PM
Tiny
BCMULLEN95
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Will charge battery, what else should I be looking for, and the liter size is 3.8L. I will be checking to see the out put of the alternator.
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Thursday, December 29th, 2011 AT 9:47 PM
Tiny
KHLOW2008
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Have you checked the fuses?
Did you check for battery voltage at the relays?
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Friday, December 30th, 2011 AT 7:34 PM
Tiny
BCMULLEN95
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I checked all the fuses and I checked for resistance from the plug to the relay and it checked out okay. I have not checked the voltage at the relay as of yet.
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Friday, December 30th, 2011 AT 8:21 PM
Tiny
KHLOW2008
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You need to check for voltage to understand if it is power supply fault.
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Friday, December 30th, 2011 AT 8:29 PM
Tiny
BCMULLEN95
  • MEMBER
  • 249 POSTS
I do have voltage to the relays, I tested alternator and it is reading 11.56V I will be checking to make sure it is connected correctly and having it tested. If the alternator is not working correctly then there is not enough power being sent to the relays to have them turn on right?
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Monday, January 2nd, 2012 AT 6:11 PM
Tiny
BCMULLEN95
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Just out of curiosity which wire from the four pin connector should be connected to the red wire in the harness?
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Monday, January 2nd, 2012 AT 7:11 PM
Tiny
KHLOW2008
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The alternator showing 11.56 volts means it is not charging correctly. It should show between 13.5 to 14.5 V.

Red wire should be connected to terminal marked " L ".
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Monday, January 2nd, 2012 AT 7:29 PM
Tiny
BCMULLEN95
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  • 249 POSTS
I finally got it put back together. I connected red wire to terminal L and it still is only reaching 11.50V Is there something else I should be looking for? Had alternator tested and it passed the test. Should I have it tested again?
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Saturday, February 11th, 2012 AT 6:24 PM
Tiny
RASMATAZ
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Get the alternator tested again
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Saturday, February 11th, 2012 AT 6:26 PM
Tiny
BCMULLEN95
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If it comes back okay is there something else I should look at?
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Saturday, February 11th, 2012 AT 6:29 PM
Tiny
RASMATAZ
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Check the wiring and the computer controlled of the alternator field generation circuit-
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Saturday, February 11th, 2012 AT 6:39 PM
Tiny
KHLOW2008
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Is the voltage at alternator main mast 11.5v as well?
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Saturday, February 11th, 2012 AT 7:06 PM
Tiny
BCMULLEN95
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It didn't matter what connector wire I used all of the gave a reading 11.56V right at the battery and at the wire on the alternator.
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Saturday, February 11th, 2012 AT 7:17 PM
Tiny
KHLOW2008
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Attached is a schematic of the charging circuit. Ensure you have battery voltage at the Red wire when ignition switch is turned on.

The main mast should have battery voltage with engine not running and charging voltage with engine running.

If you are not able to get the correct charging, the alternator is faulty. A bench test sometimes do not work.
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Saturday, February 11th, 2012 AT 7:38 PM
Tiny
BCMULLEN95
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Will a alternator not sending the right charging voltage cause the fans to not turn on.
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Saturday, February 11th, 2012 AT 8:54 PM

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