P0597: Thermostat Heater Control Circuit Open
What to do
Driveable, and you will probably notice nothing. The engine simply loses the ability to fine-tune its running temperature, which costs a little fuel economy. Worth fixing, but not urgent unless the temperature gauge is misbehaving.
What this code means
An open circuit on the thermostat's electric heater. Map-controlled thermostats carry a small heating element in the wax capsule so the module can force the thermostat open earlier than coolant temperature alone would — which lets the engine run hotter for efficiency at light load, then be deliberately cooled under high load.
With the heater open the thermostat simply behaves as an ordinary mechanical one. Nothing dramatic happens, which is why this is easy to leave: the engine runs hotter than intended at high load and slightly cooler than optimal at light load, costing a little economy and, over time, working the cooling system harder than the designer intended.
Likely causes
Start here
- Failed thermostat heater element · moderate
- Broken wire in control circuit · moderate
- Corroded or loose connector · easy
Rare
- Control module driver failure · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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