Technical Description of OBD-II Trouble Code
The thermostat heater control circuit is experiencing high voltage.
What does that mean?
This is a generic powertrain diagnostic trouble code (DTC) that applies to all makes and models from 1996 onwards. However, the specific troubleshooting steps may vary depending on the vehicle.
The codes P0597, P0598, and P0599 all refer to an electronically controlled engine thermostat. These codes are generic and apply to all vehicles that use this type of thermostatic control. However, only a small number of manufacturers utilize this system. Therefore, this trouble code article is essentially the same for all three codes.
The P0599 code indicates a fault in the system where the control voltage is high. This system is primarily used in German manufactured vehicles such as BMW, Mercedes, Audi, Mini, Volkswagen, Opel, and Jaguar.
The electronically controlled thermostat consists of various temperature and load sensors, a computer program, and the control housing with a built-in thermostat.
Concept
By electronically controlling the coolant flow or engine temperature, fuel economy can be increased and emissions can be reduced during part throttle, while reducing the temperature under load can increase power.
Symptoms
The symptoms of a P0599 code will vary depending on the position of the thermostat at the time of failure. However, it is unlikely that there will be any noticeable difference in the operation of the vehicle.
Potential Causes
Based on experience, the problem usually lies in a loose or corroded electrical connector, or the electrically operated thermostat itself is faulty. Occasionally, the Motronic (engine management) computer may fail, but this is the least likely cause.
Diagnostic and Repair Procedures
This information should include the identification of the pins and their location, wire colors, pin values in volts at specific temperatures, and resistances. These values and diagnostic procedures may vary depending on the manufacturer and engine size.
You will also need an infrared temperature probe and a volt/ohmmeter.
