P0599 Code: Thermostat Heater Control Circuit High

Reviewed by

Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Written by CarParts.com Research Team - Updated on June 12th, 2024

Reading Time: 3 minutes
Summary
  • Diagnostic trouble code (DTC) P0599 stands for “Thermostat Heater Control Circuit High.” This code is triggered when the powertrain control module (PCM) detects an incorrect signal from the thermostat.
  • The P0599 code is caused by wiring or connector problems, thermostat failure, coolant leaks, or PCM failure.
  • Common symptoms of the P0599 code include an illuminated check engine light, inconsistent cooling fan operation, and inconsistent temperature readings.

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.

Code P0599 is logged when the PCM detects an incorrect signal from the 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 and P0598.

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?

What are the Common Symptoms of the P0599 Code?

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.

Where to Get a New Thermostat to Clear DTC P0599

DTC P0599 is logged whenever the PCM detects a problem with the thermostat, specifically if there’s an incorrect signal. Fortunately, if clearing it requires replacing the thermostat, you won’t have any issues finding a new one at CarParts.com.

To start shopping, visit our website or download our mobile app. Use the vehicle selector and search filters to check out compatible thermostats that match your preferred brand, price, specs, and more. If you have questions, our team of customer service representatives will give you all the help you need to find what you’re looking for.

We source our thermostats from the most trusted manufacturers in the industry for guaranteed fit and performance. In addition, our warehouses are strategically located across the US, meaning you can receive your order within a few days.

Clear code P0599 in no time. Shop for a replacement thermostat today and take advantage of our unbeatable deals!

About The Authors
Reviewed By Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Written By CarParts.com Research Team

Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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Published by
CarParts.com Research Team and Richard McCuistian, ASE Certified Master Automobile Technician