Body, generic

B0278 HVAC Defrost Door Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

B0278 appears neither in J2012 tables nor in factory service material, so its existence is open. By its title it covers the electrical side of the defrost door actuator, the flap that routes air to the windscreen. Saab's 9-3 climate module stores the matching fault as B0240 06 (actuator circuit open or grounded) and B0241 01 (short to battery or excessive current); both lead to wrong air distribution. Hitachi's US5181553A drives the defroster door with a dedicated actuator motor, and MOTOR magazine describes how such actuators are tested electrically. A dead circuit leaves the door parked, so demisting may be weak or air may blow at the screen constantly. Door position problems without an electrical fault fit B0205.

Likely causes

Defrost door actuator motor open or shorted internally
Actuator wiring under the dashboard damaged or connector loose
Door or linkage seized so the motor draws excessive current
Actuator driver in the climate control module failed

Symptoms

  • Windscreen clears slowly because little air reaches it
  • Air keeps blowing at the windscreen whatever mode is selected

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–400
Time0.5–3 h

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

Parts involved

hvac defrost actuatorhvac control module

Related codes

B0205B0273

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