I am trying to locate the cooling fan resistor on a 2012 GMC Sierra. My issue is the fan comes on high a few minutes after starting the vehicle with the heater on. I have checked the fuses, relays, thermostat, and replaced the temp. sensor with no luck. Some mechanics told me it was the blower motor sensor under the dash on the passenger side. I changed it out and that's not it. I'm thinking the cooling fan resistor must be around the radiator. The only code it has is B0423_04
The radiator cooling fan
When the cooling fan turns on it is always on high. I never see the low side turn on.
are you having issues with your radiator cooling fans or blower motor for your HVAC cabin? Two different parts that require two different diagnostic procedures.
Both cooling fans are supposed to run on both low speed and high speed.
Are you saying that one fan isn't running?
Yes, only the right fan is blowing on high
The radiator fans don't have a resistor and the computer can't command just one fan to come on
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Here's how it's wired: I just highlighted the fan relay control wires from the PCM to show that the computer can either energize the Low Speed Relay by itself or when it wants High Speed it energizes Both the Fan Control Relay and the Fan High Speed Relay (Cool/Fan Relay 1 in the diagram) TOGETHER, along with keeping the Low Speed Relay energized
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And the way you'd test this is to grab a paperclip and bend it into a "U" shape. Pull out the Fan Lo Relay and jump relay sockets 30 & 87. When you do that both fans should run on Low Speed
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If one fan doesn't run, then disconnect that fan's wiring connector and use a test light to check that it's getting Power and Ground
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If that connector is getting power and ground then that fan motor has failed and you'll have to replace the fans
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If that fan's connector isn't getting Power then it has to be the Fan Control Relay is stuck with the Load Side in the "energized position"
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I found a video of a guy showing exactly which of those Low Speed Relay sockets to jump with a paperclip (It's a 2009 so his Fan Fuses are numbered differently than yours but the relays are the same)
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The only thing is that he makes a comment that could be confusing. He says ,if the Fan Control Relay activates with the Low Speed Relay only the drivers side fan will receive power and it will spin faster
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He doesn't make it clear that it should never happen and if it is happening it's likely that the Fan Control Relay has failed with the Load Side of the relay in its "energized position
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Here's the video:
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https://www.youtube.com/watch?v=txodmJIsDUQ
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((don't take 8 months to come back and tell us what you found out and if you need help on how to do the testing just ask))
I am trying to locate the cooling fan resistor on a 2012 GMC Sierra... I'm thinking the cooling fan resistor must be around the radiator.
There is no cooling fan resistor.
It runs either in series or parallel with the driver's side fan. The circuit is controlled by the three FAN relays in your underhood fuseblock (LO,HIGH,CNTRL) and FAN1 , FAN2 fuses. Try testing those.
The only code it has is B0423_04
the passenger side HVAC temperature blend door is malfunctioning.
Look for service bulletins such as these
https://www.tsbsearch.com/GMC/08-01-39-009B
https://static.nhtsa.gov/odi/tsbs/2016/MC-10119054-9999.pdf
https://static.nhtsa.gov/odi/tsbs/2015/MC-10139339-9999.pdf
https://f01.justanswer.com/MissileTechnician/4aba323e-1bb1-4f84-aca8-2ed9576c9cb8_Tahoe+Blendoor.pdf
The radiator cooling fan
Is the cooling fan staying on high all the time? Or what’s is it actually doing?
No it shuts off for about 2-3 minutes then back on again
Ok there is a lot of grey area here. Is it coming on really high then shutting of then high again? Like if it’s overheating? Also what’s the coolant temperature when that is happening? Cooling fans are supposed to turn off and an on so what your saying may be normal operation. Need a little more info to help.
I haven't checked the temp. with the scan tool but it turns on high a minute or two after I start it then turns off then on again after a few more minutes. This happens continuously before it reached normal operating temp. while the heater is on. The truck has never done this before since I've owned it, 6 yrs. To answer your question I would say it would start at 140 degrees.
So this only occurs with the heater on? What about when the heat is off?
It doesn't come on unless the heater is on
I would be looking at the A/C pressure sensor and connector. Look for corrosion on the connector if ok. You will need a good scan tool to monitor the ac pressure sensor and see what the voltage is at or what psi it’s reading. A bad pressure sensor could make fans turn on high when it’s not supposed to. Also would look into thermostat and the ECT. Make sure to use OEM parts. A stuck thermostat will also cause this issue.