Thermostat Heater Control Circuit High
P0599 is an OBD-II trouble code that indicates thermostat heater control circuit high. This page explains what the code means, what issues may trigger it, common symptoms and where to look next.
P0599 code meaning is one of the most common OBD-II searches when a warning light appears on the dashboard.
Drivers searching for P0599 usually want to know what the code means, whether the car is safe to drive and what part may need testing first.
Likely causes
- • Open circuit or short circuit
- • Poor electrical connection
- • Failed heater element
- • Blown fuse or wiring fault
- • Wiring or connector issue
- • Component failure in the affected system
Symptoms
- • Check engine light illuminated
Severity
Low to Medium
Can you keep driving?
Whether you can keep driving depends on how the vehicle is behaving. If there is rough running, loss of power, overheating or stalling, diagnose it as soon as possible.
Common fix areas
- • Check continuity, power and ground
- • Inspect for damaged wiring or corrosion
- • Scan all fault codes and freeze-frame data
- • Inspect wiring, connectors and grounds
- • Confirm repair with a retest after clearing codes
Manufacturer notes
FAQs
What does P0599 mean?
P0599 means thermostat heater control circuit high.
What can cause P0599?
Common causes include component failure, wiring faults, incorrect sensor readings, leaks, pressure issues or related upstream faults in the same system.
Can I keep driving with P0599?
That depends on how the car is behaving. If there is rough running, overheating, loss of power or stalling, it should be diagnosed quickly.
Does P0599 always mean I need a new part?
No. A fault code points you to a system or condition, but proper diagnosis is still needed before replacing parts.