GM has released a fix for the GMC Yukon and Yukon XL 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 GMC Yukon and GMC Yukon XL full-size SUVs.
According to bulletin PIT6373 issued by GM, 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 GMC Yukon 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
If put this comment up before. I know from experience that some 2023 GM vehicles were filled with a diluted form of coolant. I don’t know if they were running short because of covid circumstances or whatever. In my case the cure was simple. Drain some of the diluted coolant and replace with full strength. After run up the slow warm-up corrected itself. If I was a GM technician it would be the first thing I would check.
Constant poor quality on so many vehicles.