Body, generic

B0300 HVAC Evaporator Temperature Sensor Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

Public code lists do not show B0300, and factory documentation for it is missing too. The evaporator temperature sensor is a thermistor on or just behind the evaporator core; the climate controller cycles or throttles the compressor with it so that the core does not ice up (US6427465B1, US4326386A). Saab's 9-3 uses its own numbers: B0521 02 below 0.2 V and B0522 05 above 4.8 V at the module input, after which the outside temperature serves as a substitute value. HELLA reports that a badly sealed or drifting sensor can freeze the evaporator and choke the airflow. A circuit fault therefore tends to cost cooling comfort rather than leave the car without air.

Likely causes

Evaporator thermistor open, shorted or out of tolerance
Sensor pushed out of the core or poorly sealed after service
Connector at the HVAC housing loose or corroded by condensate
Sensor input in the climate control module faulty

Symptoms

  • Cooling weak or fluctuating, especially in hot weather
  • Airflow drops after a long drive because the evaporator ices up

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–500
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

evaporator temperature sensorhvac control module

Related codes

B0292B0288

References: saabwisonline.com, saabwisonline.com, patents.google.com, patents.google.com.