Electric Cooling fans staying ON with engine is OFF.

[tonyblaze]

I have a 2005 GMC 1500 Sierra 5.3 with the dual electric fans. The truck has 205K miles on it, and it has been a good truck. I bought it new in 2005.

This past week, I had to jump start the truck, since the battery was dead. After jumping it off and driving it, I got home and noticed the electric fans staying on after the engine is off and keys out of the switch. So that drained my battery.

Today, I replaced all 3 relays and the temperature sensor on the driver's side head. Well, it did not fix the problem, the fans are still running.

Does any know what I need to do next? Is there another sensor or control module for the fans?

[Badass69]

It's just 2 trigger pins from the pcm that operate the fans. Al the pcm does is ground one or the other or both depending on desired speed. Sounds like you either physically damaged something or screwed up the pcm thus it is grounding at least one of the triggers constantly. Blue connector number 33 and green number 42.

[PH-Wolf]

It is quite possible the ECM is malfunctioning, Since you replaced the temp sensor, relays, I'd check the connections and wiring making sure its not rubbed threw and feeding off other wire or grounding out,(Seen that before) Also test the ECM for any internal issues, I've seen this once a couple years ago where the ECM was malfunctioning and commanding the fans to be on all the time due to the ECM thinking the coolant temp was high and it was not, reading 235 degrees(truck was sitting overnight in the shop), Temp sensor/wiring was fine, found the ECM to be at fault and had to replace the ECM.