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Juan Crespo
Juan Crespo, Tech Trainer
Category: GMC
Satisfied Customers: 1500
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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GM Yukon Denali: Cooling fan issue. Just read Ron Z's responses

Customer Question

Cooling fan issue. Just read Ron Z's responses to another user. 05 yukon Denali. While sitting idle, over heated, started dumping AF. Just returned from a 45 mile mountainous trip. No issue noticed on the ride. Stopped and was idling when occurred. Although it wasn't an immediate thought, i know that if thoses fans were on, they'don't be screaming at that moment. Didn't think to check fan by turning on AC. I also have an existing guage issue (rpm and speedometer out of whack and stuck at times) does the guage cluster issue translate to other gauges? I dumped AF with a temp reading slightly above the 210 center mark. If when I test the low speed fan by turning on AC, and it fails, should I move forward with relay replacement? Both 40amp and 10amp fuses look good. Then.. if theres indication of power to fans, but failing to operate for engine temp extremes, should I opt to change temp sensor?
Submitted: 6 months ago.
Category: GMC
Expert:  Juan Crespo replied 6 months ago.
Hi there.We don't have access to other expert's responses, so I haven't read the ones you mention. However, I'm pretty sure I'll be able to help you solve your issue; just need a little more information:when you say "started dumping AF", where was the coolant dumping from, the cap, the reservoir, a hose?did any warning lights or messages come up on the cluster indicating the engine was overheating? If yes, what were those lights/messages?is the check engine light on or has it come on and then turned off by itself? If yes, have you had the onboard computer scanned for codes? If yes, what are those code numbers?how many miles on your Yukon?have you had your cooling system flushed? If so, how many miles ago?
Customer: replied 6 months ago.
Check engine light did not illuminate. Antifreeze began to leak from expansion tank relief under the cap to the tank. No other hoses detected to have failures. I changed the water pump, hoses, and antifreeze about 18 months ago. Vehicle has 150k miles. Didn't realize the vehicle was overheating until I saw some steam from under the hood. Guage was indicating about 210 degrees, but not by much. The AC being turned on activates at least one fan, whereas during the incident, there were no cooling fans operating.
Customer: replied 6 months ago.
I have not yet looked at ODB DTC codes, if any.
Expert:  Juan Crespo replied 6 months ago.
Thank you for that information.Cooling fans should have come on when engine temperature reached 202 degrees, regardless of whether or not the A/C was on. Since there were no indicators (check engine light, message on cluster, etc.) and engine temperature was being shown on the gauge, the cause of the overheating is probably a fault in the electric fans circuit (motors, relays, wiring, PCM).A scan tool capable of performing actuator tests is the best tool to use for the diagnosis, as it allows for the mechanic to take control of the PCM and energize the fans at will; doing this facilitates testing the circuit from the relays to the motors. Do you have access yo such a scan tool?
Customer: replied 6 months ago.
That is one tool that I do not have access to.
Expert:  Juan Crespo replied 6 months ago.
Not having that tool means we could test each motor and relay to make sure they're in working order, but we couldn't test any of the circuits and components that control them. Do you want to do that?

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