Thermostat Heater Control Circuit Open
The P0597 code indicates that the engine control module (ECM) has detected an open circuit in the thermostat heater control circuit. This heater is part of an electronically controlled thermostat that helps regulate engine temperature more precisely. An open circuit means the heater is not receiving power or has failed, preventing the thermostat from opening at the correct time, which can lead to poor engine performance and increased emissions.
1. Most Common Causes
- Faulty electronically controlled thermostat (internal heater resistor open circuit)
- Open circuit in the heater control wiring (cut, disconnected)
- Loose, corroded, or damaged thermostat connector terminals
- Blown fuse in the thermostat heater power supply circuit
- Internal ECM failure (control circuit driver) - rare
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine temperature gauge reading lower than normal
- Poor fuel economy
- Engine may take longer to reach operating temperature
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for any related codes.
Step 2: Visually inspect the thermostat heater connector and wiring for damage, corrosion, or loose connections.
Step 3: Test the thermostat heater resistance with a multimeter; compare to manufacturer specifications.
Step 4: Check the fuse for the thermostat heater circuit and replace if blown.
Step 5: If wiring and fuse are okay, replace the thermostat assembly (includes heater).
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally safe for short trips, but prolonged driving may cause poor fuel economy, increased emissions, and potential engine overheating or underheating. It's best to repair it promptly.
How much does it cost to fix?▼
The cost typically ranges from $150 to $400, including parts (thermostat assembly) and labor. The exact cost depends on vehicle make/model and labor rates.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.