P0597 P0597 code definition The P0597 trouble code signifies that a thermostat heater control circuit is open. What the P0597 code means If a PCM (Powertrain Control Module) stores this code, it’s because the engine’s thermostat (https://www.yourmechanic.com/services/thermostat-replacement) (https://www.yourmechanic.com/services/thermostat-replacement) is experiencing...