P0599: Thermostat Heater Control Circuit High

What does P0599 mean?

P0599 is a diagnostic trouble code indicating "Thermostat Heater Control Circuit High". The ECU is reading a voltage that is above the expected range. This can be caused by a short to power in the wiring, a failed sensor, or a connector issue in the cooling system.

Symptoms you may notice

• Check engine light (MIL) illuminated on dashboard
• Engine overheating
• Temperature gauge reading high
• Heater not working properly
• Intermittent warning lights

Common causes

• Damaged or corroded wiring harness
• Loose or disconnected electrical connector
• Failed cooling system sensor or actuator
• Blown fuse in the related circuit
• Poor ground connection

What should you do?

Schedule a diagnostic appointment at your earliest convenience. The vehicle is generally safe to drive short distances, but the underlying issue should be addressed to prevent it from worsening.