Thermostat Heater Control Circuit / Open
Your engine's thermostat heater isn't getting power or has a broken wire connection, like a lamp that won't turn on because the cord is unplugged. The ECU detected an open circuit in the heater control system that warms the thermostat for faster engine warm-up.
The ECU sends a voltage signal to command the thermostat heater element on and monitors the circuit for proper current draw and voltage feedback. It expects to see a specific resistance and current flow within the heater control circuit. If the ECU detects zero current or open-circuit voltage (no load resistance), it sets the P0597 fault code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Heater Circuit Resistance | 4-15 ohms (varies by vehicle) | Infinite ohms (open circuit detected) |
| Control Signal Current | 0.5-3.0 amps during heater activation | 0 amps or below minimum threshold |
Code P0597 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0597 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.