P0599: Thermostat Heater Control Circuit High
10 vehicles · 6 makes · $60-$1,800 repair
Most Reported On
P0599 is an OBD-II diagnostic trouble code meaning “Thermostat Heater Control Circuit High.” This code relates to the engine cooling system's thermostat heater control circuit, used on engines with an electrically heated (map-controlled) thermostat that the computer can open early to fine-tune coolant temperature. The 'high' designation means the computer detected the control circuit voltage was higher than expected, indicating an electrical fault such as a short to voltage or an open circuit. It is generally an electrical/wiring problem rather than a mechanical cooling failure. It can affect how precisely the engine manages its operating temperature and fuel economy. This code is most commonly reported on 2007-2016 MINI Cooper, 2015-2020 Mercedes-Benz GLA (GLA250), and 2007-2017 Jeep Patriot, plus 7 other vehicles, with repair costs ranging from $60 to $1,800.
Common Causes
Typical Repair Cost
Based on 11 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
To diagnose P0599, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
- Read & clear engine codes
- View freeze frame data
- I/M readiness status
- No batteries or app needed
BlueDriver Pro Bluetooth Scanner
by BlueDriver
Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
- Enhanced diagnostics (ABS, SRS, transmission)
- Repair Reports with verified fixes
- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X OBD-II Scanner
by LAUNCH
A professional-grade handheld scanner that reads all four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
- Engine, transmission, ABS, SRS diagnostics
- Live data stream & graphing
- AutoVIN for vehicle identification
- Free lifetime updates via Wi-Fi
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
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Vehicles Affected (10)
Thermostat Housing Coolant Leak / Cracking
Engine Overheating / Water Pump and Radiator Fan Failure
Thermostat Housing Coolant Leak
Engine Overheating / Cooling System Failures
FAQ
What does P0599 mean?
P0599 stands for "Thermostat Heater Control Circuit High." This code relates to the engine cooling system's thermostat heater control circuit, used on engines with an electrically heated (map-controlled) thermostat that the computer can open early to fine-tune coolant temperature. The 'high' designation means the computer detected the control circuit voltage was higher than expected, indicating an electrical fault such as a short to voltage or an open circuit. It is generally an electrical/wiring problem rather than a mechanical cooling failure. It can affect how precisely the engine manages its operating temperature and fuel economy.
What are the most common causes of P0599?
The most common causes of P0599 are: Faulty electronically heated thermostat element/heater, Short to voltage in the heater control circuit, Open or damaged wiring/connector, Corroded or loose connector at the thermostat, Poor electrical ground, Faulty PCM/ECM driver (less common). The specific cause varies by vehicle.
How much does it cost to fix P0599?
Repair costs for P0599 range from $60 to $1,800, depending on the vehicle and root cause.
Which vehicles are affected by P0599?
Au7o has documented P0599 across 10 vehicle models from 6 manufacturers: BMW, Chevrolet, Dodge, Jeep, MINI, Mercedes-Benz.
Sources (12)
- Forum2015 Water Pump Failure - Mercedes GLA Forum
- ForumWater Pump issues does replacement work - Mercedes GLA Forum
- ForumWater Pump Failure - Mercedes GLA Forum
- ForumThere goes the Water Pump - Mercedes GLA Forum
- ForumJeepPatriot.com - Thermostat Housing Discussion
- newsMyJeepPatriot.com - Common Problems and Solutions
- partOEM Thermostat Housing Assembly 68003582AB
- NHTSACarComplaints.com - 2006 Commander Engine & Cooling (173 complaints)
- mediaDodge Caliber Overheating - 700R4TransmissionHQ
- mediaDodge Caliber Running Hot - 700R4TransmissionHQ
- ForumOverheating issue needing help - Dodge Caliber Forums
- ForumWheres the radiator fluid going - Dodge Caliber Forum
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.