2019 GLS450 Heating issue
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Joined: Feb 2026
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2019 GLS450 Heating issue
So i have an issue with my wifes 2019 GLS450 that has been driving me mad.
About last month on a trip up north to the cottage the car lost heat. After doing some research i assumed that the aditive pack in the coolant tank had ruptured and it had clogged up the system.
I then got a new expansion tank a new auxiliary water pump did 2 coolant flushes but nothing changed. Now when checking the pipes that go to the heater core inside the dash both the in and out are hot. So i know the core is not plugged.
I hooked up the scanner and looked for codes but there is absolutely nothing present. After doing the blend door calibration some heat started coming.
I then took appart the entire lower portion of the dash took off the flap motors lubed everything up checked for any play or damages but everything looks good.
I started the car and let it get to temperature and it started blasting heat properly, while having all motors off and me opening and adjusting all the flaps manually. Now with everything working properly i put it all together drive it around for a bit and it all seems fixed. Or so i though.
Now what im experiencing is full heat out of the rear vents and weaker hot air out the front. The fan speed works properly im referring to the temperature itself. The front vents output is colder than the rear. After driving the car for an extended period of time trough town the front vents dont get as hot as the rear and driving at highway speed loweres their temperature a few degrees more. While the rear maintains proper heat under all conditions.
Someone please point me in the right direction as there are no codes or errors for any of the hvac components when scanned.
About last month on a trip up north to the cottage the car lost heat. After doing some research i assumed that the aditive pack in the coolant tank had ruptured and it had clogged up the system.
I then got a new expansion tank a new auxiliary water pump did 2 coolant flushes but nothing changed. Now when checking the pipes that go to the heater core inside the dash both the in and out are hot. So i know the core is not plugged.
I hooked up the scanner and looked for codes but there is absolutely nothing present. After doing the blend door calibration some heat started coming.
I then took appart the entire lower portion of the dash took off the flap motors lubed everything up checked for any play or damages but everything looks good.
I started the car and let it get to temperature and it started blasting heat properly, while having all motors off and me opening and adjusting all the flaps manually. Now with everything working properly i put it all together drive it around for a bit and it all seems fixed. Or so i though.
Now what im experiencing is full heat out of the rear vents and weaker hot air out the front. The fan speed works properly im referring to the temperature itself. The front vents output is colder than the rear. After driving the car for an extended period of time trough town the front vents dont get as hot as the rear and driving at highway speed loweres their temperature a few degrees more. While the rear maintains proper heat under all conditions.
Someone please point me in the right direction as there are no codes or errors for any of the hvac components when scanned.
Newbie
Joined: Feb 2026
Posts: 5
Likes: 1
Hi. Check what the interior temperature sensors show in xentry. I had similar thing today when car was toward the sun. Outside was -13C but sun heats sensors (so it thinks it's warm in the car) and air wasn't blowing hot. My windshield was cold to touch but xentry shows windshield temperature +32C. Once I started driving away from sun everything went back to normal in 2mins
Thread Starter
Newbie
Joined: Feb 2026
Posts: 2
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Hi. Check what the interior temperature sensors show in xentry. I had similar thing today when car was toward the sun. Outside was -13C but sun heats sensors (so it thinks it's warm in the car) and air wasn't blowing hot. My windshield was cold to touch but xentry shows windshield temperature +32C. Once I started driving away from sun everything went back to normal in 2mins
If you are referring to the outside air temp sensor the car was showing -8. I have not checked the cabin ones under the dashboard
