GM has issued a technical bulletin that instructs diagnosing and fixing a common problem where owners of 2019-2021 Chevrolet Silverado and GMC Sierra or 2021+ Chevrolet Tahoe/Suburban, GMC Yukon, or Cadillac Escalade may experience poor interior heating performance.
General Motors testing has indicated that there are typically two possible reasons for poor heater performance on these models. Both potential problems show up first on the driver’s side.
The vehicle models affected by poor heater performance include
- 2019-2021 Chevrolet Silverado
- 2019-2021 GMC Sierra
- 2021 Chevrolet Tahoe
- 2021 Chevrolet Suburban
- 2021 GMC Yukon
- 2021 GMC Yukon XL
- 2021 Cadillac Escalade
There may be two possible causes for the poor heater performance on these models:
- The heater core may have become plugged
- The physical links that connect to and control the temperature control doors within the HVAC control system may have become disconnected
Fixes for poor heater performance on these models will include:
Dealership technicians have a few options to diagnose potential heater issues. They may use a borescope to watch the internal doors of the HVAC unit open and close as the temperature is adjusted. If the doors are not opening and closing as needed, a technician will need to disassemble the HVAC control system and find out the root cause, typically a link that has become disconnected.
Another potential problem may be a heater core clog. If the HVAC doors are found to be opening and closing correctly, a technician will diagnose your coolant system. They will look for sludge that may have built up in the lines, that there is enough coolant in the overflow bottle, and that there are no leaks.
If any contaminants or sludge is found, they will flush the coolant system and refill with an appropriate mix of anti-freeze and water.
Have this problem with your vehicle? Here’s what you can do.
If you are an owner of one of these vehicles and have poor heating performance, your dealership will be able to help diagnose the problem. If you believe one of these symptoms may be the reason, refer your dealership to Technical Document PIT5818.
If your vehicle is out of warranty, your independent repair shop can also complete these diagnostics. Just let them know that one of the HVAC door linkages may have come undone and/or the coolant system could need to be flushed.