This process allows the mechanic to ensure that no unnecessary repairs are performed.
After this step, and every sequential step, it is important to clear the P0599 code from the PCM, and retest the system. After that, the mechanic should first check the coolant level, and be sure that there are no leaks that need repairing. The P0599 code should first be verified with an OBD-II scanner.
How does a mechanic diagnose the P0599 code? If the thermostat malfunction happens after the engine is already at the correct temperature, there may not be any noticeable symptoms at all. In addition to the illuminated Check Engine lamp, vehicle owners may observe an overheating engine in cool weather, or an engine that cannot reach optimal temperature very quickly in warm weather. The symptoms that can be present with the P0599 code can vary greatly depending on the position of the thermostat at the time of the malfunction.