05 sierra 1500 5.3 4x4 electric cooling fans not engaging

wolfautojimmy · April 21, 2016

I recently purchased a 2005 GMC Sierra 1500 5.3l 4x4 from my brother in law. When delivered to my house, it had several issues, and since the cooling fans are run through the pcm I'll tell you all the little things in case it is connected somehow. 1) intermittent radical speedometer (all other guages work fine) will read 10-70 mph faster than you are actually going 2) "Y" fitting coming off of water pump going to coolant res and to firewall was leaking 3) P0480 CEL "cooling fan relay" and niether cooling fan engaging.

What I've done:

1) replaced leaking fitting

2) Tested 3 relays for fan (2 of them were 4 prong and i energized 2 terminals, heard a click and tested for 0 resistance between other two terminals and these checked out fine by those standards) 1 fan relay is a 5 prong and I don't know how to test it but when circuit was energized the middle terminal still had resistance (70a i think)

3) found and replaced 2 40 amp fuses that had blown.

RESULTS:

Ran truck with A/C at full blast. Truck reached 210 and passenger side fan engaged to full speed and ran for about 10 minutes so I turned of a/c and the fan continued to run a few minutes then blew a fuse. Around this time, I noticed a burning smell and it seemed as if the driver side fan was smoking so I turned off truck. Turned on truck and driver side fan kicked on and ran about 60 seconds before blowing second fuse. Touched the metal part of fan and it scorched the tip of my finger.

Question: I am new to GMC trucks and electric fans. I understand that the PCM sends signals to the fans because of information received from a coolant temp sensor and apparently something to do with the a/c. I do not know if the fans run simultaneously or if one is different from the other. I was also under the impression they run at low speed before high speed. Can I rule out a major issue such as PCM? can I rule out temp sensor? did I not properly test relays and it could be a relay? Could the fans be turning on but still be the culprit? Any help at all is much appreciated.

rjgti · April 21, 2016

ohm out the fans

wolfautojimmy · April 21, 2016

How?

rjgti · April 21, 2016

use an dmm set to ohms and undue the connecter and check them

wolfautojimmy · April 22, 2016

So maybe I didn't make it clear that I don't know how to "check them" with a multi meter I don't know what I'm looking for so I took the fans out and jumped them to the battery. Both had signs of overheating and burned oil looking substance that looked like oil. One fan ran when jumped and one did not. Why would both fuses be blown? Why does the fan that runs still have signs of overheating and smell slightly of burned electrical inside

rjgti · April 22, 2016

they sound like they need replacement. that smell is windings that have shorted

wolfautojimmy · April 25, 2016

So the fans were the problem. I ended up removing th fan assembly and jumping each motor. One was Siezed and the other was dragging. $320 later and a very simple easy job and my p0480 is cleared