HVAC Evaporator Temperature Sensor Circuit Malfunction
What does B1317 mean?
The B1317 code means the vehicle's onboard diagnostic system has detected: HVAC Evaporator Temperature Sensor Circuit Malfunction. This is a moderate severity code.
Common Symptoms
- AC blows warm air intermittently
- Evaporator icing or freezing up
- AC compressor short cycling
- Inconsistent cooling performance
- AC system warning light or message
Probable Causes (Ranked by Likelihood)
- Failed evaporator temperature sensor Very High
- Corroded sensor connector in HVAC housing High
- Sensor displaced from evaporator fins Moderate
- HVAC control module sensor input failure Low
Step-by-Step Diagnostic Procedure
-
Read evaporator temperature sensor data with scan tool
-
Compare sensor reading to actual evaporator surface temp
-
Inspect sensor connector for corrosion or moisture
-
Check sensor resistance and compare to specifications
-
Verify sensor is properly seated in evaporator fins
Frequently Asked Questions
What does the evaporator temperature sensor do?
It monitors the evaporator core temperature to prevent it from freezing. When the evaporator gets too cold, the sensor signals the system to cycle the compressor off to prevent ice buildup.
Why does my AC freeze up?
If the evaporator sensor fails and reads a warmer-than-actual temperature, the system will not cycle the compressor off, allowing the evaporator to freeze. This blocks airflow and reduces cooling.
Is the evaporator sensor easy to access?
On most vehicles, the sensor is located inside the HVAC housing near the evaporator core, which can require removal of the glove box or part of the dashboard to access.