What it means
The map-controlled thermostat - electrically heated to lower its opening temperature on demand for emissions or torque mapping - has an open control circuit. The ECU loses the ability to override coolant flow timing.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
An electrically heated thermostat lets the control module influence when coolant begins flowing through the radiator. P0597 sets when the module detects an open in the thermostat heater control circuit, preventing that adjustment; engine warm-up or temperature behavior may change.
Common causes
Most likely first.
- Open in heater element or harness
- Pin pushed back out of connector body
- Cracked solder joint inside the module or sensor
Symptoms
- Check-engine light
- Engine may take longer to warm up or run hotter than usual
- Temperature gauge may behave unusually
How to diagnose it
- Use a scan tool to confirm P0597 and review freeze-frame data, coolant temperature, and thermostat-heater command to see when the open was detected.
- With the engine cool, inspect the thermostat heater connector and harness for a loose plug, damaged wire, corrosion, or a pushed-back terminal.
- Check continuity through the heater circuit and thermostat element using the wiring diagram to locate the open.
- Wiggle the harness while monitoring the circuit or repeating the scan-tool check to reveal an intermittent connection.
- If the wiring is intact, test the heated thermostat and control circuit against the manufacturer's specification.
Common fixes
- Reconnect a loose thermostat heater plug and secure its wiring.
- Repair an open or broken wire in the heater circuit.
- Replace damaged or corroded connector terminals.
- Replace the thermostat assembly if its heater element fails testing.
Can I keep driving?
You can usually drive if the temperature gauge stays normal, but watch for overheating or unusually slow warm-up. Stop if the engine overheats, since continued driving can cause serious engine damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.