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2006 GMC Sierra cooling fans question.


soulweeper

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I have a 2006 GMC Sierra, 1500 2WD, 5.3L engine. I have 33,000 miles on it, for whatever it's worth. A couple weeks ago, I was going up a small hill in first or second, can't remember....and I noticed the temp go up a bit, which I'm sure is normal, but it wasn't that steep of a hill, and I wasn't on it very long, but it went back to normal when I got where I was going. Didn't think much of it, and it might do that every time I go uphill, but I don't remember it going much above normal since I bought it. I will say that I don't stare at my gauges every two minutes, but I'm pretty good at keeping a eye on them, so maybe I never noticed this going uphill before.

 

 

Anyway, it made me keep an eye on the water temp a little more than normal, just to be safe. I was going up another little hill a few days later...same thing. Again, didn't think much of it. The other day, I came home from work in the afternoon, after about an hour drive, truck at normal temperature, a 65 degree day....pulled in the driveway, truck was still running while I was writing down my mileage in my record book, and I noticed the temp go up just a bit. Nothing you call overheating, but going up above normal. So, I popped the hood, just to see if anything seemed weird, or coolant was low....anything. One thing I noticed was that my cooling fans weren't on.

 

Now, I'm not a mechanic, but I know some of the basics, but I'll admit I don't know exactly how the electric fans work. My last truck still had a fan that simply turned with the engine, and I bought this new, so I've just been driving it, not learning every aspect of it.

 

So, after a couple more minutes that day, the fans kicked on, and the temp came back down to normal. So....when are they supposed to come on, or not supposed to be on? The next morning, after I started the truck to go to work, I popped the hood right away, and they weren't on. I'm assuming that's normal, as the truck wasn't even up to normal temperature yet. My question is simply what can I look for to give me some idea if they're working properly? Are they thermostatically controlled or do they come on over a certain speed???

 

Any input would be greatly appreciated. Thanks in advance!

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Here's a little info from an 05 model.....I'm going to assume it's the same for an 06.

 

Cooling Fan Control - Two Fan System
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:
1. Engine coolant temperature exceeds approximately 94.5°C (202°F).
2. A/C refrigerant pressure exceeds 1447 kPa (210 psi).
3. 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:
1. Engine coolant temperature exceeds approximately 104.25°C (220°F).
2. A/C refrigerant pressure exceeds approximately 1824 kPa (265 psi).
3. 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.

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Here's a little info from a 05 model.....I'm going to assume it's the same for an 06.

 

Cooling Fan Control - Two Fan System

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:

1. Engine coolant temperature exceeds approximately 94.5°C (202°F).

2. A/C refrigerant pressure exceeds 1447 kPa (210 psi).

3. 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:

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

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

3. 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.

...and that my friends sounds like an awesome answer. Thanks for posting that up.

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They come on at a certain temp and also are forced on when you use the AC generally. For what it's worth I've been in some miserably hot weather and never seen the temp gauge budge but my truck is also a different model year so the gauges may respond differently.

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Thanks for the reply.

 

I did read somewhere that they come on when the AC is used. I tried that yesterday, and they didn't kick on, but I'll have to try it again today. If I hit the AC button, should they come on right after, is it that simple? And if not, what might that indicate as the problem?

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I also have an 06 and mine don't always come on right away when the AC is on. I personally haven't seen my temp raise above normal except when I driving "the grapevine" in California while fully loaded and towing my travel trailer. It didn't go up but a notch or two but it was enough for me to turn off the AC for a few miles. I'm not sure what the specs are of the temps the fans kick on/off. I'd take it to a dealer/good shop that can scan and check out the setting to verify everything is running within normal. Also no the fan will not kick on right away when you first start it up in the morning, unless you live in Phoenix in the summer time...brutal, fans never shut off while engine running. The fans on a 65 degree day will cycle on and off, depending on speed, load, etc, etc.

 

You said the engine temp goes up just sitting in your driveway? I know you only have 33k miles (which is amazing to me, I've got 104k) but it is possible your thermostat may beginning to stick a little an staying closed a little more than it should. Do you know if the coolant system has ever been serviced?

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They should BOTH be on with the AC on.

 

One is temp controlled by the PCM, the other always comes on with the AC.

Ok.....so beyond the shadow of a doubt, if I go out and start my truck, and turn on the AC, they should both come on?? If not, where do I start to fix the problem?

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They should BOTH be on with the AC on.

 

One is temp controlled by the PCM, the other always comes on with the AC.

Ok.....so beyond the shadow of a doubt, if I go out and start my truck, and turn on the AC, they should both come on?? If not, where do I start to fix the problem?

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Unless ur in northern Alaska, AND when the truck is warmed up to the 190~ operating temp, yes.

I tried it today......when I was out and about running errands. I pulled over, popped the hood, and turned on the AC, and they cam on, so that seems o.k. According to the previous post, the fans won't come on while idling, unless it's at 202 degrees. For the most part, that needle stays right below the middle mark, which is labeled 210. The increments seem to be more than 10 when you count them, but just to the left of the middle mark is essentially "normal" Stock gauges probably aren't super precise.

 

But yeah, after coming home the other day, just sitting in the driveway, it went up past the middle, the fans came on, and it dropped, but that "seems" more like a thermostat that might be starting to act up.

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Sounds like they're working just fine to me but if you really want to find out get yourself a scanner and hook it up to your obd2 port and monitor the temperature and fan operation.

Is that an expensive item? Where do you get them?

 

I'm about to order a Hypertech Speedometer/Odometer Recalibration Programmer because I'm changing the tire size, and it's not cheap at all, for what it does, but I'm using this credit card promotion, so some of the sting is coming out of the price, haha.

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