Body, generic

B0305 HVAC Sun Load Sensor Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

B0305 is unconfirmed by any public J2012 list or manufacturer, and its subject matches B0156. The sun load sensor is a photodiode on top of the dashboard that tells automatic climate control how much solar heat enters the cabin (US6888120B2, US5957375A). Real codes for it carry other numbers: Saab's 9-3 uses B0183 08 for an implausible signal and B0184 06 for an open or grounded circuit, and then regulates as if the sky were overcast; the GM-built 2011 Saab 9-5 reports B0183 02/05. A circuit fault rarely stops the system, but in strong sun the cabin tends to run warm and the blower reacts late.

Likely causes

Sun load sensor photodiode aged or damaged
Sensor unclipped from the dashboard grille, connector pulled off
Signal or ground wire to the sensor open or shorted

Symptoms

  • Cabin too warm in bright sunshine with auto climate
  • Blower speed does not rise when the sun comes out

Repair estimate

DifficultyEasyDIY possible
Parts and labour€30–200
Time0.3–1 h

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

Parts involved

sun load sensorhvac control module

Related codes

B0156B0162

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