Jump to content
  • Sign up for FREE! Become a GM-Trucks.com Member Today!

    In 20 seconds you can become part of the worlds largest and oldest community discussing General Motors, Chevrolet and GMC branded pickups, crossovers, and SUVs. From buying research to owner support, join 1.5 MILLION GM Truck Enthusiasts every month who use GM-Trucks.com as a daily part of their ownership experience. 

Recommended Posts

Fellas and Gals! 

I am having a problem with my cooling fans not coming on my 2006 GMC Sierra, 5.3. I can force them on by running the A/C constantly. But if the A/C isn’t on, the fans won’t come on till the truck reaches almost 230 degrees F, which I’m on the road to cracking a head at the temp. I’ve already replaced the fans, thermostat, engine temp sensor,  checked to make sure I’ve got good water flow through my radiator, I’ve replaced all three cooling fan relays and I’ve checked the wiring harness. The fans will come on when I reach in there and manually unplug the harness from the temp sensor while the truck is running and it sometimes will throw a code after that. The only thing I can imagine may be happening is the CPU is not sending the ground signal to command the fans to come on when the engine reaches the appropriate temp (≈ 202, without the A/C being on). Has anyone ever experienced the CPU messing up and not send a ground signal to the system, what am I missing? S.O.S.  PLEASE SEND HELP!! 

Link to comment
Share on other sites

Check the resistance of the temp sensor against specifications.

Measure resistance of the temp sensor at the sensor. Then pull wire harness from cpu, measure resistance in the wire harness, should be the same or close.

Now the tough part. Resistance in the sensor increases as the temp rises- reducing the voltage on the return leg. Unplugging the sensor creates high resistance, and 0 voltage, enough to cross the threshold set by the cpu. A short on the return leg could be sending incorrect voltage signal back. Unplug the sensor, check for shorts with either leg against all other wires in the harness.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.