Service VME - Inadequate Heater Performance on the Drivers Side - core heat HVAC intermittent

When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

Product reports and Technical Assistance cases have recently been received on vehicles that exhibit a concern with the heater not getting hot enough or maybe just the driver’s side not getting hot enough. Back flushing the heater core often resolves the concern but sometimes only temporary. Analysis of returned heater cores as well as the material retrieved from them reveals a restriction resulting from the addition of stop-leak pellets. The Denso high efficiency heater core is designed with smaller core tubes that transfer heat with less volume of coolant flow. Stop-leak material will accumulate in the smaller tubes restricting and eventually stopping the flow of coolant. Although stop-leak pellets have been widely accepted in the industry for past applications, until further notice, use of these materials is prohibited for the CTS. Engineering is currently reviewing the system design as well as other materials that could possibly be used.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.