Will a faulty BMW thermostat trigger a fault code?
2 Answers
BMW thermostat failure will trigger a fault code. Below are specific symptoms of thermostat damage: Observe for water flow: Open the coolant reservoir filler cap and check if there's coolant circulation inside. If not, it indicates a damaged thermostat or debris stuck between the main valve switches. Thermostat response test: Remove the thermostat from the vehicle and boil it in water to observe whether it opens as the water temperature rises. Check hose temperatures: Start the engine and feel the upper and lower radiator hoses after 3 minutes. With a properly functioning thermostat, the upper hose should be hot while the lower hose remains cool, indicating normal operation.
Over the years of running a repair shop, I've seen many BMWs with thermostat issues. If the electronic thermostat gets stuck or has wiring problems, the dashboard immediately lights up with a yellow warning, and the diagnostic tool often shows a P0597 control circuit fault. The most typical symptom is the coolant temperature gauge needle refusing to rise, with the engine staying in the cold zone even after warming up for half an hour. Once, a customer's car had the check engine light constantly on, with OBD showing P0128 (coolant temperature too low). Upon disassembly, we found the thermostat valve jammed by scale deposits. The newer G-series models are more sensitive - any abnormal valve opening directly triggers power limitation. Never ignore a faulty thermostat - cooling system chaos can lead to cylinder scuffing, and the repair cost would far exceed a thermostat replacement.
