Electric Cooling Fans

[JPVortex]

Hello, all my 2005 Tahoe's cooling fans are not coming on no matter what. This is an ongoing issue, that while the truck stays steady at 205-210 while moving, it does climb a bit while sitting at idle for 15+ minutes. Direct 12 volts to the fan shows that they work, so it's wiring for sure.

Tried swapping out all of the relays for known working ones and the fuses to no avail.

Does anyone have a wiring diagram for the fan assembly? May try cleaning up the relay center or getting a new relay center. I may also try finding a ground to clean up.

If I really can't be bothered I'll just wire it to the ignition so it's always on.

 

[Doubeleive]

Hello, all my 2005 Tahoe's cooling fans are not coming on no matter what. This is an ongoing issue, that while the truck stays steady at 205-210 while moving, it does climb a bit while sitting at idle for 15+ minutes. Direct 12 volts to the fan shows that they work, so it's wiring for sure.

Tried swapping out all of the relays for known working ones and the fuses to no avail.

Does anyone have a wiring diagram for the fan assembly? May try cleaning up the relay center or getting a new relay center. I may also try finding a ground to clean up.

If I really can't be bothered I'll just wire it to the ignition so it's always on.

have you tested the fans? nevermind I see that now
have you checked fan harness? if there is voltage at the relay and the fans work with 12v applied then there has to be a break somewhere in between.

 

[Scottydoggs]

try unplugging the temp sensor, both fans should come on full speed, if they do replace the temp sensor.

 

[Doubeleive]

try unplugging the temp sensor, both fans should come on full speed, if they do replace the temp sensor.

he said the temperature gauge shows normal temps while driving and gets hot when stopped, I would presume the sensor is working properly
and I totally missed he tested the fans already lol

 

[Scottydoggs]

he said the temperature gauge shows normal temps while driving and gets hot when stopped, I would presume the sensor is working properly
and I totally missed he tested the fans already lol

temp sensors are two part, one side goes to the cluster, other to the pcm. pulling the plug off the temp sensor should default the fans to hi speed, showing the relays work.

 

[mattbta]

The gauge on the cluster is notoriously inaccurate. From what I gathered when researching parameters for tuning my PCM when doing this swap on my 2004, the factory has low speed fan turn-on at 226* which seems way high. I set mine at 205* and have only had them come on once one the 3 or 4 drives since install.

Do they come on when you turn the A/C on?

 

[JPVortex]

The gauge on the cluster is notoriously inaccurate. From what I gathered when researching parameters for tuning my PCM when doing this swap on my 2004, the factory has low speed fan turn-on at 226* which seems way high. I set mine at 205* and have only had them come on once one the 3 or 4 drives since install.

Do they come on when you turn the A/C on?

will try with the coolant temp sensor unplugged. And no with AC on they do not turn on.

 

[mattbta]

Another thing to test could be unplugging the connector from the fan harness to the PCM. Then on the end that runs to the relay box you can ground the green wire for low speed or blue for high. That should tell you if it is harness/relay related.

 

[Rocket Man]

If you know somebody with a Tech2 you could command them on and see if the PCM is telling them to turn on.

 

[JPVortex]

Another thing to test could be unplugging the connector from the fan harness to the PCM. Then on the end that runs to the relay box you can ground the green wire for low speed or blue for high. That should tell you if it is harness/relay related.

Ok, wouldn't I need to give power to the part that goes into the PCM too aswell as ground aswell? Or wait actually the relays would give it power.

And to ground it would I just splice into the wire and run it to a good ground?

 

[JPVortex]

Ok, wouldn't I need to give power to the part that goes into the PCM too aswell as ground aswell? Or wait actually the relays would give it power.

And to ground it would I just splice into the wire and run it to a good ground?

Or I could probably just put an alligator clamp on the connector

 

[Fless]

You might think about pulling both PCM connectors off to inspect for water migration and pin fitment. IIRC the fan pins are at the bottom of the connector and that's where the water goes if it gets in. Just something to check.

 

[JPVortex]

You might think about pulling both PCM connectors off to inspect for water migration and pin fitment. IIRC the fan pins are at the bottom of the connector and that's where the water goes if it gets in. Just something to check.

Yeh thatd be a good idea, I'll first test the connector by sending ground with those wires

 

[JPVortex]

Another thing to test could be unplugging the connector from the fan harness to the PCM. Then on the end that runs to the relay box you can ground the green wire for low speed or blue for high. That should tell you if it is harness/relay related.

Do you have a picture of which connector goes to the PCM?

Also from what you said I'm guessing that the way the PCM turns the fan on and off is by cutting ground? Since I'd be grounding the wire?

 

[mattbta]

The connector with the two small gauge wires in the middle of this picture is what I’m talking about. Disconnect that connector. You will want to ground to the relay side (left in the pic), take a spare wire and touch to negative battery terminal and then to one of the pins inside that connector. Green for low or blue for high.

The two small wires with tiny pins in the picture go to the PCM. Don’t do anything with that side of the connector. (The PCM supplies, not cuts, ground when the fans are activated.)

If the fans turn on, then it’s not the relays or harness.

Make sure to plug it back in.

 

[JPVortex]

View attachment 391236The connector with the two small gauge wires in the middle of this picture is what I’m talking about. Disconnect that connector. You will want to ground to the relay side (left in the pic), take a spare wire and touch to negative battery terminal and then to one of the pins inside that connector. Green for low or blue for high.

The two small wires with tiny pins in the picture go to them PCM. Don’t do anything with those. (The PCM supplies, not cuts, ground when the fans are activated.)

If the fans turn on, then it’s not the relays or harness.

Make sure to plug it back in.

Ok thank you very much. I will perform this test tomorrow as itll be like 45 farenheit out compared to 15 lol.

 

[JPVortex]

Did run out quick to test the temp sensor. Fans did not kick on with it unplugged, kind of expected that

 

[JPVortex]

Well heres an update yall, did the test and the fans do kick on! So it's some sort of PCM issue. I have a spare PCM but it might be for a pre 2005 truck that doesnt have electric fans.

also wondering if my pcm was replaced at one point and the electric fans weren't enabled in it.

 

[Rocket Man]

Have you removed the connectors at the PCM and looked for corrosion? It’s fairly common like @Fless mentioned. The PCM is located under the battery and has 2 large connectors with 8mm screws holding them on iirc. You’ll have to loosen those and wiggle the connector to get them off. Disconnect the battery first of course. There’s an o-ring on each one but sometimes water still gets in. You should be able to tell if the PCM has been swapped by looking at it. If it’s undisturbed looking then it’s probably original.

 

[JPVortex]

Have you removed the connectors at the PCM and looked for corrosion? It’s fairly common like @Fless mentioned. The PCM is located under the battery and has 2 large connectors with 8mm screws holding them on iirc. You’ll have to loosen those and wiggle the connector to get them off. Disconnect the battery first of course. There’s an o-ring on each one but sometimes water still gets in. You should be able to tell if the PCM has been swapped by looking at it. If it’s undisturbed looking then it’s probably original.

Yeah I have the PCM off right now. I see no corrosion what so ever on it.