Cadillac ATS A/C off due to high engine temperature with check engine light, possible thermostat issue on Cadillac ATS

Some Cadillac ATS owners report experiencing the "A/C off due to high engine temperature" message along with the check engine light, which may indicate a problem with the engine thermostat. These owners often find that the P0128 trouble code suggests the thermostat is stuck open, preventing the engine from reaching the correct operating temperature. Additionally, the A/C is automatically disabled to prevent overheating when the Powertrain Control Module detects excessive heat or if the electric cooling fan is malfunctioning. Other issues such as low coolant levels, a clogged radiator, or a faulty radiator fan may also trigger this warning. Some owners note that switching to a lower temperature thermostat can affect the engine's ability to reach the expected temperature, potentially leading to sensor issues flagged by the ECM. If the thermostat and related components are not inspected and replaced promptly, these issues can persist, necessitating further tuning and adjustments.