Description of the P0599 fault code.
OBD2 Error Codes

P0599 Thermostat Heater Control Circuit High

26.05.2022 /

P0599 – OBD-II Trouble Code Technical Description

Trouble code P0599 indicates that the PCM has detected a signal level too high in the thermostat heater control circuit.

What does the fault code mean P0599?

Trouble code P0599 indicates the thermostat heater control circuit is too high. This means that the vehicle's ECU (Electronic Control Unit) has detected that the voltage in the thermostat heater control circuit is higher than the manufacturer's limit. The thermostat heater may be malfunctioning or malfunctioning, which can cause problems with engine temperature control and engine efficiency.

Fault code P0599.

Possible reasons

Possible reasons for DTC P0599:

  • Thermostat heater malfunction: The thermostat heater itself may be damaged or failed, resulting in faulty engine temperature control and increased voltage in the control circuit.
  • Short circuit in control circuit: A short or open in the thermostat heater control circuit can cause voltage instability and lead to P0599.
  • Problems with temperature sensors: Failure of the temperature sensors that transmit signals to the ECU to control the thermostat heater may cause the system to malfunction and cause an error to occur.
  • Electrical fault: Problems with the wiring, connectors, or connections in the thermostat heater control circuit may cause the voltage level to be too high and cause the P0599 code.
  • ECU problems: Malfunctions or errors in the operation of the electronic control unit (ECU) itself, which controls the operation of the thermostat heater, can lead to the appearance of this fault code.
  • Insufficient engine cooling: If the thermostat heater is not working properly due to a malfunction, it may result in insufficient engine cooling, which in turn can cause serious engine performance problems.

It is important to conduct a comprehensive diagnostic to determine the exact cause of the P0599 code.

What are the symptoms of a fault code? P0599?

With DTC P0599, the following symptoms may occur:

  • Unstable engine temperature: A malfunctioning thermostat heater can result in unstable operation of the cooling system, which may result in fluctuations in engine temperature.
  • Increased fuel consumption: Insufficient engine temperature stability due to a faulty thermostat heater can lead to increased fuel consumption.
  • Performance degradation: If the engine is running too cold due to a malfunctioning thermostat heater, engine performance may be reduced, resulting in loss of power and poor throttle response.
  • Increased emissions of harmful substances: Insufficient engine temperature can lead to incomplete combustion of fuel and increased emissions of harmful substances, which may lead to violation of environmental standards.
  • Errors appearing on the dashboard: In some cases, the ECU may activate the “Check Engine” light on the dashboard to alert the driver of a problem.
  • Problems with interior heating: If the thermostat heater is not working properly, it may result in insufficient heating of the vehicle's interior in cold weather.

If you notice one or more of these symptoms, it is recommended that you have your DTC P0599 problem diagnosed and repaired by a qualified auto mechanic.

How to diagnose a fault code P0599?

To diagnose DTC P0599, you can follow these steps:

  • Checking fault codes: Use the OBD-II diagnostic scanner to read trouble codes from the vehicle's ECU. Verify that the P0599 code is indeed present.
  • Visual inspection of the thermostat heater: Check the thermostat heater for visible damage, corrosion, or breaks in its wiring. Carefully inspect the connections and connectors.
  • Checking the voltage in the control circuit: Using a multimeter, measure the voltage at the thermostat heater control circuit. Normal voltage should be within the limits specified in the technical documentation for your car.
  • Checking the thermostat heater resistance: Using a multimeter, measure the resistance of the thermostat heater. The normal resistance will be indicated in the technical documentation for your vehicle. If the resistance is not within specifications, the thermostat heater may require replacement.
  • Checking temperature sensors: Check the operation of the temperature sensors, which provide information about the engine temperature to the ECU. Failure of these sensors can result in a P0599 code.
  • Checking wiring and connectors: Check the condition of the wiring and connectors in the thermostat heater control circuit for corrosion, breaks or damage.
  • Checking the operation of the computer: If there are no problems with the thermostat heater, carry out additional diagnostics of the operation of the ECU, since the problem may be related to improper operation of the control unit itself.
  • Checking the ECU software: Check for ECU software updates as software errors can cause P0599 to appear.

After identifying and eliminating the cause of the P0599 code, it is recommended to test the cooling system and check for other trouble codes.

Diagnostic errors

When diagnosing DTC P0599, the following errors may occur:

  • Misinterpretation of data: Incorrect reading or interpretation of data obtained from a multimeter or scanner may result in an incorrect diagnosis. This may occur due to incorrect connections, selection of incorrect measuring ranges, or misunderstanding of technical parameters.
  • Skipping factors: Some mechanics may skip some important diagnostic steps such as checking wiring and connections, which may result in incorrectly identifying the cause of the error.
  • Failure of new components: When replacing components such as the thermostat heater or temperature sensors, faulty or incompatible parts may be used and the error will persist.
  • Insufficient knowledge and experience: Errors may occur due to insufficient experience or knowledge in diagnosing cooling systems and vehicle electronics.
  • Hardware problems: Incorrect use or malfunction of diagnostic equipment may result in incorrect diagnostic results.
  • Skip additional checksNote: Failure to perform additional checks or tests to identify other possible causes of the P0599 code may result in an incomplete diagnosis and failure to correct the underlying problem.

To prevent these errors, it is important to contact qualified technicians with experience in engine management systems and use the correct diagnostic equipment.

How serious is trouble code P0599?

Trouble code P0599 can be serious, especially if the problem is not resolved promptly or is ignored:

  • Potential engine cooling problems: The thermostat heater plays a key role in regulating engine temperature. If it is not working properly due to a P0599 code, it can cause the engine to not cool properly, which can ultimately lead to overheating and serious engine damage.
  • Increased fuel consumption and emissions of harmful substances: Improper operation of the thermostat heater can result in inefficient fuel combustion, which can increase fuel consumption and emissions, harming the environment.
  • Decreased productivity: Insufficient engine temperature due to a malfunctioning thermostat heater can result in reduced engine performance, which affects the vehicle's performance and handling response.
  • Potential Security Issues: If the thermostat heater does not operate properly and causes the engine to behave unpredictably or cause poor engine performance, it can create dangerous situations on the road.
  • Possible damage to other components: Incorrect engine temperature can cause damage to other cooling system and engine components, which may require costly repairs.

Based on the above factors, it is recommended that you take the P0599 trouble code seriously and resolve the problem as soon as possible to avoid serious consequences for your vehicle and road safety.

What repair will help eliminate the code? P0599?

Troubleshooting DTC P0599 may include the following repairs:

  1. Replacing Thermostat Heater: If the thermostat heater has failed or is not functioning properly, it should be replaced with a new one. This usually involves removing the old heater and installing the new one according to the manufacturer's instructions.
  2. Checking and repairing the electrical circuit: Check the wiring, connectors and connections in the thermostat heater control circuit for corrosion, breaks or other damage. Replace damaged components or wiring as necessary.
  3. Checking and replacing temperature sensors: Check the operation of the temperature sensors, which provide information about the engine temperature to the ECU. If necessary, replace faulty sensors.
  4. Checking and updating ECU software: Check for ECU software updates as software errors may cause DTC P0599 to appear. If necessary, update the software to the latest version.
  5. Additional tests and diagnostics: If necessary, perform additional tests and diagnostics to identify other possible causes of the P0599 trouble code, such as checking the operation of the ECU and other cooling system components.

After repairs, it is recommended to test the cooling system and scan fault codes to ensure that there are no errors and that all components are operating correctly. If you are unsure of this work, it is recommended that you contact a qualified auto mechanic or service center to perform repairs.

How to Fix P0599 Engine Code in 2 Minutes [1 DIY Method / Only $11.97]

P0599 – Brand-specific information

Trouble code P0599 can occur on various makes of vehicles, some of them are:

Please refer to your vehicle brand's specific repair manual for more detailed information about the P0599 code and its solution for your specific vehicle.

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