Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the car's computer has detected a problem with the heater that helps control the engine's thermostat. It's like the heater is getting too much power.
The P0599 code indicates that the thermostat heater control circuit is receiving a higher voltage than expected.
The thermostat heater is an electrically controlled device that helps regulate the engine's temperature by opening and closing the thermostat. The Engine Control Module (ECM) monitors the voltage in the thermostat heater control circuit. If it detects a voltage level that is higher than the specified range, it triggers the P0599 code.
• Check Engine Light is on
• Engine overheating
• Poor fuel economy
• Faulty thermostat heater
• Wiring issues such as short circuits or open circuits
• Faulty Engine Control Module (ECM)
ECM: Engine Control Module, the computer that controls engine functions.
Thermostat: A device that regulates the engine's temperature by controlling coolant flow.
• Use an OBD-II scanner to confirm the P0599 code is present.
• Inspect the thermostat heater and its wiring for damage or disconnections.
• Check the voltage and ground connections to the thermostat heater.
• Replace the thermostat heater if faulty.
• Repair or replace damaged wiring or connectors.
• Replace the ECM if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $400
Moderate
• Chevrolet Cruze
• Volkswagen Jetta
• Ford Focus
• Regularly inspect and maintain the cooling system.
• Ensure electrical connections are secure and free from corrosion.
• Use the correct type of coolant for your vehicle.
Sensor Issue
• Do not ignore the Check Engine Light; get the vehicle inspected promptly.
• Monitor the engine temperature gauge for signs of overheating.
• Avoid driving long distances until the issue is resolved.
Check with your vehicle manufacturer to see if the thermostat or related components are covered under warranty.
This code has become more common with the introduction of electronically controlled thermostats in modern vehicles.
Moderate – Addressing this issue promptly can prevent engine overheating and potential damage.
Driving with an overheating engine can cause severe damage and may not be safe. Address this issue promptly to ensure vehicle safety.
• Engine at operating temperature
• Electrical system fully charged
The thermostat heater is typically located near the engine's thermostat housing.
Q: Can I drive my car with a P0599 code?
A: It's not recommended, as it can lead to engine overheating and further damage.
Q: How can I reset the Check Engine Light after fixing the issue?
A: Use an OBD-II scanner to clear the code, or disconnect the battery for a few minutes.
High-End · Full-system diagnostics
A full-system bidirectional platform aimed at advanced DIY users and professional diagnostic workflows.
Network faults often require full-system access instead of a generic code reader alone.
View on Amazon
Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
View on Amazon
Universal · Wire connectors and repair kit
Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
View on AmazonThese are optional diagnostic tools, not guaranteed fixes. As an Amazon Associate I earn from qualifying purchases.
Fitment Required · Vehicle-fitment part
Relevant when coolant-temperature and warm-up faults indicate a thermostat-related issue.
Coolant-temperature and warm-up faults often lead to thermostat testing and replacement.
Thermostats are vehicle-specific and should be matched by engine and housing style.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.