Code p0599, coolant system?

2019 CHEVROLET TRAX

62,000 MILES • 4.0L • 4 CYL • 2WD • AUTOMATIC

NBM1961

MEMBER
11 POSTS
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after getting code p0599, I found a leak at the thermostat and water pump, replaced both, checked for leaks and found none. Drove the car for about a half hour no problems. shut it off waited 30 minutes, turned it on and the p0599 code came back on. what am i missing?

Apr 14, 2025 at 7:37 PM

STEVE W.

CAR REPAIR CONTRIBUTOR
15,167 POSTS

P0599 is for a thermostat heater control circuit high voltage. The circuit is fed voltage in on the Violet w blue wire, the PCM turns the heater on and off using PWM voltage on the blue wire. The heater controls the thermostat through the connector on it. You can test the circuit using a meter to measure the resistance between the two terminals on the thermostat. It should be between 13-15 ohms for a good heater. If that test is okay, then the next step is to use a test light and touch the connector for the Violet wire on pin one. If you have voltage there and the heater tests good then the next check is to see if there is an issue in the heater control side, that is the blue wire on pin two. The easy way to test that part of the circuit you need a scan tool.

This video is the same system and shows the testing process:
https://www.youtube.com/watch?v=uM0iTg7mXWA

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Apr 14, 2025 at 11:56 PM

NBM1961

MEMBER
11 POSTS

Multimeter is showing 4.5 ohms. Is thermostat bad or not?

Apr 15, 2025 at 9:07 AM

STEVE W.

CAR REPAIR CONTRIBUTOR
15,167 POSTS

4.5 is very low and should be replaced. Sounds like you got a bad one.

Apr 15, 2025 at 9:38 AM

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