Could be the temperature sensor is bad.

 

If the sensor was bad, I wouldn't think I should be able to read my temperature on dash or on the scanner. Or is there another input?

 

True. It must be sending some signal. But I have heard the dash gauge is not super accurate. More of a dummy gauge if you will within a range. If you have an OBD2 type reader you can see what the actual number is. I use a bluetooth adapter in mine and the Torque app on my phone to see it.

 

Check the ground in the PCM and maybe check the actual temp with an OBDII tool. I had a similar thing on my caprice and it came on at around 225°F. Dash showed around 240°F

 

Thanks, I am checking it with my OBDII reader, and it gets up to 220F and fans didn't come on. I will check the grounds though! Thanks

 

I am not sure what temp they should be kicking on at...but that is right around normal operating temp there at 220°F.

 

Saw this in depth post on another site:

The PCM commands the low speed cooling fans ON under the following conditions:
•Engine coolant temperature exceeds approximately 94.5°C (202°F) .
•A/C refrigerant pressure exceeds 1447 kPa (210 psi) .
•After the vehicle is shut OFF if the engine coolant temperature at key-off is greater than 101°C (214°F) the low speed fans will run for a minimum of 60 seconds . After 60 seconds , if the coolant temperature drops below 101°C (214°F) the fans will shut OFF. The fans will automatically shut OFF after 3 min. regardless of coolant temperature.

The PCM commands the high speed fans ON under the following conditions:
•Engine coolant temperature exceeds approximately 104.25°C (220°F) .
•A/C refrigerant pressure exceeds approximately 1824 kPa (265 psi) .
•When certain DTCs set.
At idle and very low vehicle speeds the cooling fans are only allowed to increase in speed if required. This insures idle stability by preventing the fans from cycling between high and low speed.

This is why I'm concerned. This says low speed fan on at 202F, High Speed fan on at 220F. Mine aren't coming on at all (unless I ground blue & green wire at PCM). I'm going to check a friends truck to see when fans come on (same year model).......

 

If this info is correct, what I assume, the fans should kick on.. Atleast the low speed fan. Your High Speed Fan might come on at 221 or a tad higher depending on the accuracy of the sensor.
Were you able to check the PCM grounds? But with the PCM Grounds beeing the issue shouldn´t there be more problems?

 

My thoughts exactly. I'll double check the grounds just in case. And check another truck for fan temp operation. I'll keep you posted!

 

Did you try jumping power to your fans? Make sure they come on first before you go too much further. I can't see them crapping out but stranger things have happened.

 

When I ground the Green & Blue wires at the PCM, the fans cut on. Tells me the circuit from PCM to fans are fine.

 

Ok here's what I've done. I have removed both PCM connectors and ohmed all ground wires to chassis & battery ground. All ohmed good. Reconnected and started truck. Hooked OBD 2 scanner to read engine temp. Coolant temp climbed to 227F and fans never came on.

I completely removed the green and blue wire from the PCM connectors. I ground them, and the fans cut on. The PCM is not completing the ground to start fans.

Does anyone know if there are 'cooling fan parameters' in the PCM that could have changed? My OBD 2 scanner doesn't read parameters like this....

Again, any help would be great! I appreciate the help so far...

 

I going through the same issues with my truck. I'm planing on opening up the ecm today to see if there is any thing wrong with the board.

 

I will see when I get to my shop with the scan tool.

 

Thanks man! Let me know what you find! Thanks

 

I can't find anything for setting parameters in the scanner.

 

That's what I was afraid of... Its really pointing towards a PCM.

 

Have you come across a solution for your problem? I have now where else I can search. I'm looking into a ecm swap.

 

Yeah I'm thinking the same thing. I may have come across a pcm to try. I'll let you know!

 

I have the same year, make and model and this has helped me eliminate a lot of possibilities when mine started doing the same thing. Did you ever end up having to replace the PCM?

Thanks again, this thread saved me a lot of time!

 

Hi guys I am having similar issue with my 2011 fans won’t come on even if I turn on the ac . I have replaced the relay and temp control sensor for them . I’ve bypassed the relay and they spin fine .

 

Bumping this thread. My '07 Classic is having the exact same issue right now. No fans, A/C doesn't work, no fans when A/C is selected on the control panel. I've replaced all fan relays, fuses checked fine, replaced coolant temp sensor. Fans turn on if I jump the relay slots 30 to 87. I've even swapped ECUs and still no change.

 

Easy way to test is with BIDI controls from a scanner or tuning software. That lets you test everything from the PCM/ECM to the fans in one try.

 

Alternately/as well, you can try doing electrical testing instead of throwing parts at the truck. Could be a wiring or connector problem somewhere, or perhaps the hvac head unit has a problem.

 

if the refrigerant lever is low, it will not come in either. You could just short out the refrigerant pressure switch and see if it comes on or alternatively disconnect the coolant temperature sensor.

That's what happened to mine
twice

 

Hello everyone I have had a problem also with my Electric fans not turning on when at temp mine was the relay on the fans but I also switch to a manual fan and clutch to stop the over heating

 

What year/make/model/engine/trim truck?