Heater Coolant Temp Sensor Open Circuit
The HVAC control module or battery energy control module (BECM) in hybrids/EVs has detected an open circuit in the heater coolant temperature sensor. This sensor monitors the temperature of coolant flowing to the cabin heater core or the high-voltage battery thermal management system. An open circuit prevents accurate temperature readings, potentially affecting heating performance or battery thermal regulation.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty heater coolant temperature sensor (internal open circuit)
- Damaged, corroded, or disconnected wiring or connectors between the sensor and control module (HVAC or BECM)
- Internal failure of the HVAC control module or BECM
- Coolant leak exposing the sensor to air, causing an erroneous open-circuit reading
3. Symptoms You Will Notice
- Inoperative or weak cabin heater
- Check engine light or HVAC system warning light illuminated
- Possible reduced battery performance or thermal management issues in hybrids/EVs
4. Step-by-Step Diagnosis
Scan for related codes and check live data from the heater coolant temperature sensor
Visually inspect the sensor, wiring, and connectors for damage, corrosion, or disconnection
Test sensor resistance with a multimeter and compare to specifications
Check for coolant leaks near the sensor
If sensor and wiring are okay, test the control module for proper signal reception
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, but cabin heating may be reduced or inoperative. In hybrids/EVs, battery thermal management could be affected, so it's best to address the issue promptly.
How much does it cost to fix?▼
Typically $150 to $400, depending on the sensor cost, labor, and whether the control module needs replacement.