Cooling Fan stayed on killed my battery 05 Silverado

woodja

Original poster
Member
Dec 24, 2012
14
05 Silverado 5.3, 113000 miles. Parked for a week - seldom driven- battery was dead. 6 month old battery.
Hooked up a charger there was some clicking in the relay / fuse box when i first connected the charger to the battery and the cooling fan began running - right side only.
Put the key in and turned on, wont start but fan shut off. Left the charger hooked up and went away for an hour or so. Came back and the fan is on again. Battery is charged up. Started the truck let it run for a few minutes and shut it off.
Fan stayed on again and battery draining rapidly.
What could cause the fan to stay on until the battery is dead? Block temp sensor, relays?
 

Sparky

Member
Dec 4, 2011
12,927
What does the temp guage read when the engine is cold but the fan is kicking on?

Could just be a bad relay also.
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Try swapping the fan relay with another one of the same type and see if it persists. If it does, time to break out the meter and check where the power is coming from. Having schematics would help (download the manual from the link in my signature).
 

woodja

Original poster
Member
Dec 24, 2012
14
thank you, ill try the relay swap and see if that solves it. ill post back after it try that.
 
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woodja

Original poster
Member
Dec 24, 2012
14
Well, i did try the relay swap, the condition did not improve. I continued searching for answers and found a tip. The 2 large wire connectors to the PCM (blue and Green) under the cover next to the battery. Removed them and inside the blue one was water and corroded female pin connectors (pin was corroded too). Cleaned the pin with emery, pulled the connector from the block of wires and did a good clean on it as well, air to blow the water out of everything, dielectric grease to seal the wires and connector. It worked... for 1 year.20201211_125349.jpg
The condition returned. I retried the relays just in case, swapped in new ones. No improvement. Went back to the PCM, disassembled as before. Water again in the connector and the PCM pin bay. Corrosion on the ground pin this time and the related female pin connector. Cleaned them both up again, sealed again and reassembled. It worked... for 2 months.
Yesterday i came home from work to the low speed fan running. I popped the hood to disconnect the battery until i have time to once again see what the water did to the PCM connector. This time, when i disconnected the battery ground cable the fan DID NOT stop running. Disconnected the pos cable, the fan still runs with no battery connected.
The fan is getting power supply from somewhere, im at a loss as to where. Stored capacitor power is my guess. Meant to supply power to PCM to support memory functions? I disconnected the fan wire to before it drew the power supply to zero.
Long winded i know, but does anyone have any suggestions? I plan to open the PCM connector again this wknd and see what is going on in there but at this point i am my limit as far as electrical systems go.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
What? That is practically impossible. Are there two batteries? What if you disconnect the fans? What if you turn the key to start? Is this a hybrid by any chance? There can't be that much capacitor capacity to run cooling fans for that long, even from those huge ones used for amps.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Now that is truly bizzare!!

Is there even a remote chance that you disconnected the battery while the RAP was still active and the OnStar back up battery kicked on?? I don't even know if this is possible but I have read there is a BUB (back up battery) for OnStar systems and that it activates if the main battery is ever disconnected while either the key is in the on position or the RAP is still active.
 

mushy

Member
Sep 21, 2021
1
north carolina
05 yukon xl same problem ,fans run ignition off ,runs down batt. after long trouble shooting, moisture in bottom of pcm . pins corroded and broken off. new pcm from flagship one 150.00 . 5 new pins solder in plug ,yes it was tuff taking plug apart ,got pins from dealer .extended fender well with vinyl stair tread from lowes, with zip ties. hoping to block water. sealed around plug with seal tape that seals to its self. 8 months later same problem. did not have to get new computer ,but had to put in 3 new pins. this time i took computer bracket out ,cut on it some ,raised it some and turned computer where plug faces up ,covered it with vinyl stair tread and zip ties. over 3 years now no problems.
 

Reprise

Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
Welcome to the site. Normally, I might throw some shade for posting in an old thread, but it's only about 6mos since the last update, and you may have some useful info for me (since I just converted my '03 Sierra to e-fans). So I'll cut ya a little slack, vs. being my usual anal-retentive self. :argue::popo::biggrin: (no, I'm not a mod, either... just an old fart that likes to complain... lol)

I'm not having any water intrusion issues (yet), but since you and the OP did... got any pics of what you did to mod yours with? (actually, I can visualize a bit of it, since you reoriented the PCM on its side to have the connectors / pins facing upward).
Thanks in advance, if you post them! :tiphat:
 

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