P0597 means the engine control module has detected an open circuit in the thermostat heater control circuit. The thermostat heater is used on electronically controlled thermostats to modulate coolant flow; when the heater circuit is open, the heater cannot operate, which may affect engine warm‑up and temperature regulation.
The internal heater winding in the electronic thermostat has an open circuit, preventing it from receiving power.
Corrosion, broken wires, or a loose connector in the thermostat heater harness creates an open circuit.
The fuse or relay supplying voltage to the thermostat heater circuit has opened, cutting power to the heater.
An inadequate ground for the thermostat heater circuit can cause the PCM to see an open condition.
A failure inside the engine control module that incorrectly reports an open circuit is possible but uncommon.
No. PCM failure is rare for this code; most cases are caused by a faulty thermostat heater, wiring issue, or blown fuse/relay.
You can drive short distances, but the engine may warm up slowly or run hotter than normal, which could affect performance and fuel economy. It is advisable to repair the fault promptly.
Disconnect the heater connector and measure resistance across the heater terminals with a multimeter; an open (infinite) reading indicates a failed heater. Also check for voltage at the connector while the engine is running.
Re‑inspect the wiring harness, connectors, fuse, and relay for intermittent faults. If those are good, further PCM diagnostics may be needed, but PCM replacement is still unlikely.