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 there is a break in the electrical path, preventing the heater from functioning. This can lead to improper engine warm-up, reduced fuel efficiency, and increased emissions.
01. Most Common Causes
- Faulty thermostat heater element
- Open or shorted wiring in the heater control circuit
- Blown fuse related to the thermostat heater
- Faulty engine control module (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine takes longer to reach normal operating temperature
- Poor fuel economy
- Possible overheating or underheating
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm code P0597 and check for other 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 good, replace the thermostat assembly (heater integrated).
04. Commonly Affected Makes
05. 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 and increased emissions. In extreme cases, the engine may not reach proper operating temperature, leading to increased wear.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor. The thermostat assembly itself is often $30-$80, and labor adds $50-$100 depending on the vehicle.