GM has released a fix for the Chevy Tahoe and Suburban rear heater blowing cold air. The issue tends to occur while the SUV is at idle and sometimes persists as the engine revs. Affected models include the 2021-2025 Chevy Tahoe and Chevy Suburban full-size SUVs.
According to bulletin PIT6373 issued by the National Highway Traffic Safety Administration (NHTSA), the issue could be caused by air trapped in the rear heater core, which causes poor heater performance. Notably, this complaint does not address front heater performance.
“Some customers may comment there is cool air coming from the rear heater at idle, but when the engine RPMs are increased rear heater performance improves,” reads the bulletin. “This may be normal due to the engine RPMs at idle are low resulting in less coolant flow to the rear heater core.” In other words, if the rear air warms up when the RPMs go up, don’t take it in for service, because that’s normal.
However, if the rear air doesn’t warm up when the engine revs, it’s likely due to air trapped in the rear heater core. GM technicians are instructed to elevate the front of the vehicle and use the coolant Vac-N-Fill procedure to remove the air from the rear heater core. Of course, technicians also need to ensure the cooling system is filled to the proper level. From there, service departments should compare the rear heater performance to other GM vehicles with the same wheelbase and powertrain to see if it’s fixed.
The bulletin notes that this potential issue can apply to all engines and transmissions available in the Chevy Tahoe and Chevy Suburban from the 2021-2025 model years. These include the 5.3L V8 L84 gas engine developing 355 horsepower and 383 pound-feet of torque, the 6.2L V8 L87 gas engine cranking out 420 horsepower and 460 pound-feet of torque, and the 3.0L I6 LM2 turbodiesel Duramax engine, rated at 277 horsepower and 460 pound-feet of torque. The diesel was upgraded to the new-for-2025 3.0L I6 LZ0 turbodiesel Duramax engine, providing 305 horsepower and 495 pound-feet of torque.
Comments
Total lack of quality
This seems minor in comparison to the plethora of mechanical issues that GM is experiencing. I had an issue with slow heater warm up on a new 2023 GM vehicle. It turned out to be a weak factory installed antifreeze mixture. Draining some from the radiator at 1000 mi. and replacing with pure undiluted coolant cured the problem after a short run up.
Cheapest parts from lowest bidder worldwide any QC with engineering and down the assembly line seem to be a long lost art. Been building vehicles for over 100 years and can’t even get the simple things correct. Maybe they can sell you an additional app after your purchase of this $80 to $125k to correct all these issues after it leaves the dealer lot.
Seems like designing the rear heater inlet to be lower than the outlet would allow the unit to air free itself.
Perhaps they’ve been installing them upside down?
GM should consider an electric booster water pump to help eliminate the inadequate coolant circulation due to the long hose routing to the rear heater core or switch to a system of using a hot air duct to provide heat from the front to the back cabin areas. T. A.