What Does P0597 Mean?
The PCM has detected an open circuit or general malfunction in the electronically heated thermostat control circuit. Modern vehicles use an electrically heated thermostat to allow the PCM to precisely control engine operating temperature for optimal fuel economy and emissions. When this circuit fails, the thermostat defaults to its wax-element behavior, typically opening at a fixed temperature. The driver may notice slightly reduced fuel economy or the engine taking longer to warm up.
Common Causes
35%
Failed heated thermostat internal heater element
25%
Open or broken wire in the thermostat heater control circuit
20%
Corroded or disconnected thermostat heater connector
12%
Blown fuse protecting the thermostat heater circuit
8%
PCM driver circuit failure for the thermostat heater output
Diagnostic Steps
1
Locate the heated thermostat connector (on the thermostat housing, typically near the upper radiator hose connection) and verify the connector is securely plugged in — these connectors are exposed to engine heat and coolant leaks.
2
Measure the thermostat heater element resistance — typical values range from 10-30 ohms depending on the application; OL (open) confirms a failed heater element.
3
With the connector unplugged, check for 12V power supply and PCM ground control at the harness side — the PCM typically supplies a duty-cycled ground signal to control the heater.
4
Check the thermostat heater fuse in the fuse panel — consult the vehicle fuse diagram for the correct location and rating.
5
Monitor the coolant temperature warm-up rate using the ECT PID — a properly functioning heated thermostat allows the PCM to reach operating temperature (195-220°F) faster and more precisely than a conventional thermostat.
Estimated Repair Cost
$150 - $500
Parts + labor, varies by vehicle and location
The PCM has detected an open circuit or general malfunction in the electronically heated thermostat control circuit. Modern vehicles use an electrically heated thermostat to allow the PCM to precisely control engine operating temperature for optimal fuel economy and emissions. When this circuit fail...
The most common cause of P0597 (Thermostat Heater Control Circuit / Open) is: Failed heated thermostat internal heater element
Typical repair costs for P0597 range from $150 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. The thermostat will still function using its mechanical wax element — it simply loses PCM-controlled temperature optimization. The engine will not overheat, but fuel economy may decrease slightly and warm-up time may be slightly longer, especially in cold weather.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0597 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Engine Cooling System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
