P0599: Thermostat Heater Control Circuit High
What Does P0599 Mean?
P0599 is a diagnostic trouble code indicating: Thermostat Heater Control Circuit High. This code relates to the vehicle speed and idle control system. It has been reported in NHTSA complaints across 1 different vehicle models.
Symptoms of P0599
- ⚠️ Check engine light illuminated
Real Owner Reports
From NHTSA complaint database — actual owner descriptions.
"MY DAD AND I NOTICED THAT AFTER MY CAR HAD BEEN DRIVEN FOR AWHILE THAT THE FAN BEGAN RUNNING REALLY HARD THEN I NOTICED ABOUT A MONTH AGO THAT MY CHECK ENGINE LIGHT CAME ON. I HAD A MECHANIC CHECK IT AND HE TOLD ME THAT IT WAS CODE P0599 WHICH IS THE THERMOSTAT CONTROL CIRCUIT. HE SD THAT HE BELIEV"
— Chevrolet Cruze owner, 06/02/2016
Source: NHTSA Complaints Database
Most Reported Vehicles for P0599
Based on NHTSA owner complaint data.
| # | Vehicle | Reports |
|---|---|---|
| 1 | CHEVROLET CRUZE |
Frequently Asked Questions
Why does my car idle rough?
Can a dirty throttle body cause this?
What To Do Next
Possible Fixes
- 🔧 Have the code scanned with a professional-grade scanner to read freeze frame data
- 🔧 If DIY repair isn't feasible, get a diagnostic from a trusted mechanic ($50-150)
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1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
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2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
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3
Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.