P0599 Code: Thermostat Heater Control Circuit High

On-board diagnostic (OBD) codes are designed to help you identify possible issues with your vehicle. But before attempting any fixes to resolve the codes retrieved by your scan tool, it’s important to know exactly what they mean.

Code P0599 is one of many trouble codes that can be logged and retrieved from the OBD system. Read on to understand what this code can mean for your vehicle.

What Does the P0599 Code Mean?

Diagnostic trouble code (DTC) P0599 stands for “Thermostat Heater Control Circuit High.” This code is logged when the powertrain control module (PCM) detects an incorrect signal from the thermostat.

Some vehicles with newer engines can utilize thermostats that are electronically controlled by the PCM. The electronically controlled thermostat consists of various temperature and load sensors, a computer program, and the control housing with a built-in thermostat.

If the PCM detects an incorrect signal from the thermostat, then it might log code P0599. Code P0599 can also indicate a fault has occurred with the system where the control voltage is high.

Depending on the severity of the problem, related error codes can also be stored with this DTC. Code P0599 is similar to error codes P0597, P0598, and P0599.

Note: The definition of code P0599 might be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Common Causes of the P0599 Code?

• Wiring problem
• Thermostat failure
• Faulty connector on the thermostat
• Coolant leak
• PCM failure

What are the Common Symptoms of the P0599 Code?

• Active check engine light
• Constantly operating cooling fans
• Inconsistent temperature gauge readings

How to Diagnose the P0599 Code

The P0599 trouble code is a generic code that can be set across several makes and models. However, this does not mean there’s a one-size-fits-all approach to diagnosing its underlying cause. The steps for troubleshooting this code will vary depending on your vehicle’s make and model.

Check out this video to get an idea of what the diagnostic process for this code might involve:

How to Fix the P0599 Code

P0599 can share similar triggers and symptoms with other fault codes. However, that does not mean that they share repair steps as well. All vehicles are different, so make sure to refer to a factory repair guide that is specific to your car.

If you’re considering troubleshooting this code on your own, make sure to consult a vehicle-specific repair manual or an online repair database. These resources contain the appropriate diagnostic and repair procedures for this code. Alternatively, you can leave the job to a professional.