B0170 B0xxx · Body (B) Low severity
Evaporator Temperature Sensor Circuit
The evaporator temperature sensor reading is implausible. The A/C compressor then cannot be modulated correctly, risking evaporator icing.
Severity guidance: Low — usually no drivability impact, fix at the next service
Symptoms you will notice
- A/C cuts out intermittently
- Weak cooling
- Evaporator icing and reduced airflow
Common causes
Ordered from most to least likely — start at the top.
- 1 Failed sensor
- 2 Corroded connector at the HVAC housing
- 3 Wiring damage
- 4 Sensor dislodged from the evaporator
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Watch evaporator temperature in live data — it should stabilise just above freezing.
- ✓ Inspect the sensor and its position on the evaporator core.
- ✓ Check the connector at the HVAC housing for corrosion.
Repair options
- Replace the evaporator temperature sensor
- Re-seat the sensor correctly
- Repair the wiring
B0170 — frequently asked questions
Why does the airflow drop after 20 minutes? +
Classic evaporator icing from a sensor that reads too warm, so the compressor never backs off.
Can I keep using the A/C? +
Short term yes, but icing and compressor cycling will eventually damage the system.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.