Common Symptoms
- Check Engine Light illuminated
- Engine takes longer than normal to reach operating temperature
- Poor fuel economy during warm-up phase
- Reduced cabin heat output
- Engine temperature gauge reads lower than normal
- HVAC system blows cooler air than expected
Most Likely Root Causes
- Shorted thermostat heater control circuit to voltage
- Faulty electronically controlled thermostat assembly
- Damaged wiring harness between ECM and thermostat
- Corroded or damaged connector at thermostat
- Failed ECM thermostat driver circuit
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Component Location
The electronically controlled thermostat is typically located in the engine coolant housing near the cylinder head or upper radiator hose connection.
Manufacturer Notes
Electronically controlled thermostats became common on many manufacturers' vehicles after 2010 to improve warm-up time and fuel economy.
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