Electric cooling fans not working

Hello,

It sounds like the PCM fan control driver has gone bad not triggering the relay when hot. I would plug in a used/rebuilt PCM to see what happens here is the location of the PCM in the diagrams below. Check out the diagrams (Below). Please let us know what happens. Also I have included the fan wiring diagrams so you can see how thehyetems works.

Can you check applicable trouble codes? To check codes, yourself, at the least, you need an obd2 code reader. Some of the national brand auto stores will check codes for free? Here is a guide to help check the relay and the location featured below.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know,

I looked at info for 6.0L Silverado--1500.

I grabbed you a diagram of the cooling fan system from "prodemand"

it shows all of the components and locations

surely, you can get 'er done now!

Waiting to see your grin!

The medic

The cooling fans are controlled by the engine computer and are driven from the coolant temperature sensor which is located in the diagram below.

I would check the coolant temp sensor before the relay or the fan motor itself.

The only other thing I can suggest is did you scan for any dtc's, there could also be a trouble code. Coolant fan problems might not turn on the SES light but there could be a dtc. Also looking at the scematic there could also be a problem in the pcm because there are 2 drivers in the pcm which are relay control grounds. The pcm controls the relays. (This is just a suggestion) but there could even be a problem in the pcm. You need to use a scan tool that is able to command the fans on and off. This might help to diagnose it. Post back with other questions/answers.

Only other thing I could think of, is the coolant low or does the coolant sys have air in it, that could cause the fans to run on high.I looked at the scematic and the diagnostic it's preety straight forward, it just says to check all relays and check for a short to voltage on the motor supply voltage circuit. I also found this info on the operation of the fans, this might help. The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.

During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan s/p relay and the right cooling fan. The result is a series circuit with both fans running at low speed.

During high speed operation the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3 second delay, the PCM supplies a ground path for the high speed fan relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.

Important: The right and left cooling fan connectors are interchangeable. When servicing the fans be sure that the connectors are plugged into the correct fan.

The PCM commands the low speed cooling fans ON under the following conditions:

" Engine coolant temperature exceeds approximately 104.25 °C (220 °F).

"Â 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 107.2 °C (225 °F).

"Â A/C refrigerant pressure exceeds approximately 1824 kPa (265 psi).

"Â 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. I do't know to many more suggestions, I hope some of this info helped. If you get stuck of find any other info post back.

A quick thing to check is un plug the ecm connecters and check inside for green powder. This truck was known to have problems with the plug letting water get in and fans running all the time. Clean out the plug end and the ecm end.