Q: Engine code says my thermostat is bad but nothing seems wrong with my car.

asked by on January 09, 2017

I have a code of P0599 saying my thermostat heather control circuit high. But when my car is operating it is completely fine and nothing overheats or shows signs of error.

My car has 57000 miles.
My car has an automatic transmission.

Check Engine Light is on Inspection $79.99 - $89.99 Get a Quote

Your vehicle is probably covered by GM’s 5 year, 100,000 mile Powertrain Warranty. Consequently, you may be entitled to a free warranty repair of this thermostat issue, which issue by the way is not particularly unusual and so the dealer service department will have already encountered it and be familiar with it. Thermostat replacement may resolve the problem. However, a loose or corroded connector on the thermostat is another cause. Other reported causes are shorts or opens in the wiring harness between the computer and thermostat and rarely the control computer will fail. The existence of diagnostic trouble code P0599 on your vehicle does definitely mean there is a fault in the system but the fault does not always immediately result in a visible malfunction. Nevertheless, the efficiency of the engine is degraded simply because there is some loss in the electronically controlled thermostat’s ability to precisely control coolant flow at part throttle versus high engine load. GM should repair this for and you should definitely get it resolved as I have indicated that the fault DOES negatively affect engine performance. If you run into difficulty you can request diagnosis and repair though YourMechanic and the service to request would be a check engine light diagnostic. Please let us know if you have further concerns.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

What others are asking

Rep light is on and now wont start like not getting gas car was runing and cut off and would not re crank

You should have the computer scanned for additional codes and also check the fuel pressures to see if the no start is a computer sensor issue like crankshaft sensor or the fuel pump is not giving pressure.

Can having your engine seize cause transmission problems too?

If your vehicle has an automatic transmission, the engine drives the transmission through a fluid coupling known as a "torque converter". As a consequence of this design, if the engine were to suddenly stop, the transmission (and differential) would continue...

Are the variable valve timing solenoid and the camshaft sensor the same?

Hello. The variable valve timing and the camshaft position sensor are two separate sensors. The camshaft position sensor is more towards the front of the engine and is a lot easier to replace. The variable valve timing sensor is a...

Car starting issues

There are a number of things that may contribute to hard starting. Things like low fuel pressure, fouled spark plugs, contaminated fuel, a clogged fuel filter or a bad fuel pump are some of the things related to fueling issues...

What does the Lane Departure System Unavailable message mean?

The Lane Departure System Unavailable message can appear in the driver information center (DIC). When the DIC displays this alert, the lane departure warning (LDW) system is temporarily not working. When the LDW system issue is resolved, the DIC alert...

EVAP Vent valve solenoid code p0449

This suggests you may have a bad EVAP control module. A battery voltage is supplied to the evaporative emission (EVAP) canister vent solenoid valve. The control module grounds the EVAP canister vent solenoid valve control circuit to close the valve...

Reduced engine power

Code P0120 relates to the throttle position sensor and can be caused by the following: Sticking throttle return spring MAP or TPS connector corrosion Misrouted harness causing chafing Bad TPS Bad PCM Code P0220 relates to the...

My horn windshield wipers A/c stop working at the same time could it be a relay or any thing over 2012 Chevrolet Cruze

If they all stopped working at the same time, that raises the possibility of a "common" failure such as a circuit opening relay, fuse, fusible link, common ground, and so forth. Note though that if a "fuse" blows, it's not...

Car only drives in reverse.

Sounds like you are having transmission issues. Low fluid levels in the transmission can cause issues like this. The problem is not all cars have easily accessible ways of checking the fluid. You can check your owners manual to see...

Related articles

How a Car's Heating System Works
The The sun sets, and the air has a chill. You pause to flip your jacket collar up, and you walk briskly to your car door and slide into the driver's seat. Once you start your car, it’s only moments...
The Top 5 Selling Cars in Georgia in 2012
Georgia Georgia offers drivers a mild climate with very little snow, but rain is a major factor. Previous best-selling cars in the area, such as the Escape, Fusion and Camry, have shown that residents prefer a mix of both SUV...
The Best Used Cars to Buy If You’re a Wedding Planner
As As a wedding planner, the demands placed on your time are going to be significant, even if you’re only dealing with one or two couples. You need to be a master juggler when it comes to your time and...