2005 Silverado Engine Fans wont come on!

[Grit03]

Hello, I have been researching an issue with my engine cooling fans on my 2005 Silverado Z71, and I hope someone could help me out. Here's what's going on.

 

1) With my OBD2 reader hooked to the truck (reading engine temp on OBD2 reader), the engine temp goes up to 237F and neither low OR high speed fans come on.

 

2) After troubleshooting relays and fuses, I found that the PCM starts the low/high speed fans come on by grounding a Green wire (Connector 1 Pin 42 for LOW SPEED) OR a Blue wire (Connector 2 Pin 33 for HIGH SPEED) in the PCM.

 

3) I can physically remove the green & blue wire from the PCM, and physically ground them. Fans come on! This tells me that the circuit from the PCM to the fans is fine. The relays operate accordingly, etc. If I ground the Green, I get low speed. If I ground the Blue, I get high speed. Reinstalled wires in the connectors, and fans still wont come when engine temp reaches 237F.

 

4) Furthermore, I ohmed all PCM ground wires to  battery/chassis ground, and all were good.

 

I have no codes for the Engine Cooling Fans, and no associated codes. Are there parameters in the PCM for the engine cooling fan that could've changed? Is there a designated ground from the PCM that I'm not aware of? Is my PCM bad? Are there other components that could have failed that would cause fans not to come on (for example a faulty gauge cluster?.?>??)

Any help would be greatly appreciated. Thankyou.

[Jsdirt]

I'd test the temp sensor directly. Not sure if they still use 2 these days, but back in the day, there was 1 for the temp gauge, and another for he ECU to read.

 

I figure the computer is getting bad info. If not, the driver somehow got cooked. Maybe the fan motors are failing, and pulled too many amps? Or someone did some testing and fed battery positive directly to one or both those wires ...

 

Temp sensor would be the first place I'd look. 

[kickass audio]

I'm not sure 100% on the actual temp that you need to reach before it kicks on but you may not be quite hot enough to get the fans to want to start up.

 

If your truck is that hot try to turn on your a/c full blast and see if the fans will start up. It needs to be warm enough outside as well for it to work. 

[Doug_Scott]

How sure are you that the engine is at that temperature? Does the engine overheat?  

[Hillwood]

The fans should be on with the A/C running. You should be able to turn them on with a scan tool.
The circuits should be good then.


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[Grit03]

On 12/20/2018 at 7:17 AM, Hillwood said:

The fans should be on with the A/C running. You should be able to turn them on with a scan tool.
The circuits should be good then.


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Thanks 

[Grit03]

Im reading temp with my OBD scan tool, and it gets to 237.  I understand that low-speed fan to come on at 212°, and high-speed fans come on around 230°. I did not see any parameters where I can cut the fans on and off with the scan tool that I have (but I just ordered a new scan tool, so I'll see when it gets here).  I haven't tried the air condition yet, but I feel very comfortable that the circuit is fine due to the grounding of the wires at the PCM, and fans come on... I will try the AC though....

[Jsdirt]

By grounding the wires at the PCM, you're only verifying that the fans, their power and wiring are good - the unknowns are still the PCM itself, and the sensors it relies on in order to command the fans on.

 

Don't know where you live, but we're in a heat-wave in the Northeast right now - 61° outside. Would be a perfect day to test the A/C to at least see if the PCM is capable of controlling the fans.

[Grit03]

I agree, I will check this. I will keep you posted thank you for your help!