P0597 on Buick: How to Diagnose & Fix
Thermostat Heater Control Circuit Open
1 Buick model · 1 documented issue · 1 critical · $600-$1,500 repair
P0597 on Buick by model: symptoms, diagnosis and fix
The three-cylinder turbo cooling system uses an electrically actuated multi-port coolant control valve with a plastic housing and rotor that directs flow between the block, heater core, turbo and radiator circuits. The plastic rotor binds or the housing cracks, and the integrated water pump module can fail alongside it. Because the ECM cannot achieve commanded coolant flow, it sets a coolant-flow-low fault and the engine overheats, typically after 20-25 minutes of continuous driving. Owners describe an erratic temperature gauge that swings before the overheat warning appears. Because the valve sits in a tight three-cylinder bay, labor is a large share of the bill.
Common Symptoms
- Engine overheats after 20-25 minutes of driving
- Temperature gauge reads erratically or swings high then normal
- Engine overheat / idle engine warning message
- Heater blows cold or only warm at idle
- Coolant loss with no obvious external puddle
- Check engine light
How to Fix
Verify with a scan tool that the coolant control valve is being commanded and is actually moving, and pressure-test the system for the cracked housing. The repair is replacement of the coolant control valve assembly (and the water pump if it is leaking or noisy), followed by a full vacuum-fill and bleed of the cooling system. A partial or air-locked fill will reproduce the overheat symptom, so the vacuum fill is not optional. Do not simply top off coolant and keep driving; sustained overheating on an aluminum three-cylinder head risks head gasket and head damage.
Sources for this issue (2)
P0597 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0597 mean on a Buick?
P0597 stands for "Thermostat Heater Control Circuit Open." P0597 is a cooling-system code indicating an open electrical circuit in the control for the heated (electronically controlled) engine thermostat. Many modern engines use a thermostat with a built-in heater element that the computer can energize to open the thermostat sooner for better temperature management and emissions. When the PCM commands that heater but detects no electrical continuity (an open circuit), it sets this code. It generally means the thermostat heater isn't being controlled, which can affect coolant temperature regulation, fuel economy, and emissions. On Buick it is documented across 1 model: Encore GX.
What are the most common causes of P0597?
The most common causes of P0597 are: Failed thermostat heater element or integrated control thermostat, Open or broken wiring to the thermostat heater circuit, Corroded, loose, or disconnected thermostat connector, Blown fuse or open in the heater power feed, Poor ground or control-circuit fault from the PCM, Damaged PCM driver for the heater (rare). The specific cause varies by vehicle.
How much does it cost to fix P0597 on a Buick?
Published repair estimates on Buick range from $600 to $1,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0597 on a different make?
View P0597 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.