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Tuner in Training
I need help with programming my fan swap in my 03 Chevy Tahoe.
So I took electric fans and the factory wiring harness out of an 05 Tahoe to put in my 03 Tahoe. I have everything working and nothing is over heating and the ac works very well. I have noticed while working at an auto shop is all of the 05 chevys that come in that have electric fans both will run on low while at operating temp; while on mine, only the passenger side on kicks on high for operating temp and then the driver side will kick on high for overheating. I am curious why I can not find a way to program them the same as an 05. I have looked at the differences between a stock 05 tune and a stock 03 tune and the only thing I can find is options for Desired % vs ECT on the 03 and the 05 tune does not have that. I am afraid of messing with those numbers and would like some help. The wiring harness I have has a 3 relay setup so I know it is capable of low speed and I have tested that using an Autel scan tool to turn the different relays on.
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You didn't post your tune so I will have to assume that because you have an 03 it acts like an 03.
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Tuner in Training
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You reduced cooling fan operation on fan 1 and fan 2 by 30 degrees.
Cooling system operation 2005
Cooling System Description and Operation
Engine Coolant Indicators
ENGINE COOLANT HOT
The instrument panel cluster (IPC) displays ENGINE COOLANT HOT message when the IPC receives a class 2 message from the powertrain control module (PCM) requesting illumination of this driver warning.
ENGINE OVERHEATED
The IPC displays ENGINE OVERHEATED message when the IPC receives a class 2 message from the PCM requesting illumination of this driver warning.
LOW COOLANT LEVEL B
The IPC displays LOW COOLANT LEVEL message when the IPC receives a class 2 message from the PCM requesting illumination of this driver warning.
REDUCED ENGINE POWER
The IPC displays REDUCED ENGINE POWER message when the IPC detects a reduced engine power condition from the PCM. The IPC receives a class 2 message from the PCM requesting illumination when the engine temperature exceeds a calibrated value.
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:
Engine coolant temperature exceeds a calibrated value.
A/C refrigerant pressure exceeds a calibrated value.
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 a calibrated value.
A/C refrigerant pressure exceeds a calibrated value.
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.
Coolant Level Control (If Equipped)
COOLING FAN OPERATION 2003
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:
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.
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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Tuner in Training
So what I am getting at is that I just need to increase the turn on temps to what the 05 specs are? The only thing I am wondering is that with my factory clutch fan, my operating temp was around 198F. So if I increase these values will it cause any problems with my engine because I am not really wanting to run it that hot. Are there any other ways to change the values so the fans will activate at the low temp and run properly? Like changing the Desired % vs ECT?
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I'm not sure I get what you are trying to accomplish. You have two separate fans with the 05 config and wiring. If you want them both to come on at the same time set them to the same on and off temp. You could set them at a very low temp and put the A/C disable speed at 200mph and the fans would stay on the moment it turned on to the moment it turned off.
Are you actually having an issue that needs correcting like overheating or over cooling, or do you just not like how the fans turn on and off?
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Tuner in Training
My fans will not run on low speed. At operating temp only fan 1 comes on, on high speed and then when it gets hotter fan 2 comes on, on high speed. I don't understand why my fans will not use low speed.
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Typically you will have a 3 relay system. You can have a low speed when you run both fans in series splitting the voltage between the two motors. But to do that you need the third relay. Does the system (hardwire mechanical) you installed in this vehicle have two, or three fan relays?
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Tuner in Training
It has 3 relays. The fans and wiring harness are factory, I pulled them out of a 05 tahoe.
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Should be a wiring schematic in this forum. It has been posted many times now. Need to do a good electrical diagnostic on the wiring and relays. Might try swapping the relays and see if something changes. If it does..... bad relay
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Tuner in Training
Okay, I have already changed all of the relays and fuses because I thought that too. I'll doubt check continuity again.
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Tuner in Training
The only thing I do not understand is it should all work because like I stated in the original post. I tested all the relays by activating them with my Autel scan tool I have so I know all the relays are good and triggers the fans for low speed.
Last edited by sethdipman; 11-14-2023 at 12:51 PM.
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So both fans run in low speed when manually commanded but not when the PCM does it on its own based on temperature?
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Tuner in Training
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I don't see how that's possible. There are only two control pins at the PCM, one pin to ground for one relay to get low speed, both control pins to ground at the same time for all 3 relays to get high speed.
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Tuner in Training
I will put some videos up of what it?s doing here in a bit
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Tuner in Training
I have already tried that tune file
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2005 Tahoe:
screenshot.14-11-2023 15.25.02.png
You should test the fans without the PCM or depending on any scanner controls. Ground the wire going to C1 42 and both should run at low speed. Ground both C1 42 & C2 33 and both should run at high speed.
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Tuner in Training
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