Intermintent Cooling Fan problem

SB42 · July 2, 2014

I have electric fans on a 06’ Sierra 6.0. Twice in the last 2 months (or so) I’ve had them not turn-on when they should have been on. I happened to notice because I could smell it running a little hot and my temp gauge was all the way to 210-ish. I switched on the heat to help dissipate the extra heat. When I started the truck up a few minutes later the fans turned on and all was well. (not that it should matter but I was at 8-9K ft. both times. I know this impacts the coolants’ properties but I wouldn’t think it would have any impact on the fans themselves)

The only work that’s been done on the truck lately was some fluid flushes including the coolant. Seems unlikely that this would be related but thought I would mention it. Prior to me realizing it was the fans, I tested the coolant to ensure that the dealer put the right mixture in and it tested fine. The first time this happened I thought maybe they disconnected the fans during the flush process but verified that the connectors looked fine and since the fans have been running since, I ruled that out.

What do I need to check next? Seems odd to me that its intermittent. Seems like it’s a sensor type issue of some sort but that doesn’t quite click for me since the gauge is reading fine. Could the thermostat be acting up? I couldn’t quite wrap my head around how that would influence the fans….

Let me know what y’all think I need to check next. Much appreciated!

Sam

Chris · July 2, 2014

Are we talking a 06 Vortec Max that came with them or a 2500+ that was swapped to electric fans

SB42 · July 2, 2014

06 Stock VMax (1500) that came with them....

I've had the truck for a little over 4 years and put 45K on it.

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Chris · July 2, 2014

Change the upper and lower hoses plus the puke tank hose. Replace thermostat. And follow instructions to completely change out the Dex-Cool

8.1HD/ALLISON · July 2, 2014

I dont have specs or book for that year, but most times the fan wont kick on till its really hot. Maybe someone with SI can chime in.

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SB42 · July 2, 2014

Chris -

I'm curious about your logic. I just had the fluid flushed so I'd prefer not to replace the hoses quite yet. In hindsight probably would've been a good idea to do the hoses as good measure.

Anyone have a link handy to a write up on a thermostat replacement. Haven't done one yet and wondering what's all involved if I end up needing to go that route.

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SB42 · July 2, 2014

I dont have specs or book for that year, but most times the fan wont kick on till its really hot. Maybe someone with SI can chime in.

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Yea I agree they won't kick on until it's hot enough. In this case I'm confident they weren't on when they should've been. Just ran out and took a closer look at the gauge and I think it was actually running closer to 215 maybe staring to push 220.

Dumb question - what's SI short for?

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8.1HD/ALLISON · July 2, 2014

Service information. Gm dealer service manuals.

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8.1HD/ALLISON · July 2, 2014

Alldata says they won't kick on untill 220.

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SB42 · July 8, 2014

Alldata says they won't kick on untill 220.

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Good idea on the AllData. My subscription expired a while back and I didn't even think of that.

Still seems somewhat odd to me that it doesn't kick on until 220 but AllData had been a reliable source in my experience. I don't stare at my gauges but generally speaking it sticks around 190-195. I know the red doesn't start until 250 but that seems extreme. I've run my truck in temps above 100F. If the 220 statement is accurate it seems that I n theory my fans would never activate unless A/C was on since I can't recall ever seeing gauge above 210.

I figured out you can indirectly force the fans on by turning the A/C on. I guess next time I'm up at that altitude cruising real slow on the forest service roads I'll need to be more patient and give the fans a chance to kick on.

Maybe one of the GM advisors will chime in and provide their two cents.

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txab · July 8, 2014

You could get a tune and adjust the temp. setting for fans to kick on. Also get a scanner that can read engine data and see what the ecm is reading for temps and when the fans switch on/off. Dash gauge is not always an accurate measurement. IIRC, fans also have a low and high fan speed setting

Duelin · July 8, 2014

Most GM vehicles have their fan kick in around 228° and kick off around 214°. GM likes the engines running at this temp for a couple of different reasons. The 14° range between 228° and 214° means less expansion and contraction which means less movement between the heads and block. Which means less problems with head gaskets. Also at that heat range it keeps any moisture that is in the engine in vapor state and the engine is able to pull it out thru the PCV system. No moisture means no sludge. Also at that temp range there is less emissions. LIke txab said if you have a scanner you could look and see what temp the computer is kicking the fans on and off. And if you had an infrared thermometer you could compare the two. There is a possibility that you could have a bad CTS sensor.

bossier62guy · July 10, 2014

This is out of GM SI for an 05....most up to date info I could get.

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.

SB42 · July 17, 2014

Thanks for all the responses and info. That's what I was looking for.

Sounds as if my CTS may be going bad since it seems like intermitent issues. I'm curious how the gauge gets fed from the CTS/PCM since it seems to be working well but the fans not (well, only twice now they haven't kicked on when I feel they should have). Sounds like a good test in the future will be turning the A/C on to see if that kicks the fans on. I'll get my hands on a scanner so I can see the true temps. Hopefully I can catch the fans in the off postion while scanning. If it ends up being the CTS, from the quick research I've done it seems like that may be a simple $20 repair.

bossier62guy · July 17, 2014

The CTS signal is sent to the PCM. The PCM provides the gauge info via the class 2 serial data bus and also sends the appropriate signal to activate the fan relays. If it were my truck I'd find some way to monitor the coolant temp and watch the fans to see if they are operating per the specs above. If you have a smart phone you can buy an OBDII adapter and downlown the "torque" app. Not sure how good you are with schematics but I'm attaching them nonetheless.....once again they are for an 05. Don't over look those relays....you could have one going bad.