Body, generic

B0104 Sensor Cleaning Air Blower Actuator A Control Relay

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

B0104 points at the relay that switches power to blower A. A fan motor draws more current than a module output can carry, so a relay is a natural choice: the module energises the coil (terminals 85/86 in HELLA's scheme) and the contact (30/87) feeds the motor. HELLA's relay brochure explains that coils may carry a diode or resistor against switch-off spikes and that relays are checked for coil resistance and contact voltage drop. Faults here are an open or shorted coil, welded or burnt contacts, or a missing feed. Ford's US12115948B2 places the blower on the sensor bracket, and the Ford tiara uses that air to shield lenses from insects, as eeNews reports. No carmaker publishes B0104; the B-side relay is B0105.

Likely causes

Burnt or welded contacts in the blower A relay
Relay coil open or its control wire interrupted
Blown fuse or loose socket on the relay supply side

Symptoms

  • Blower A dead, or running without command if contacts are welded
  • No relay click when cleaning is requested
  • Sensor cleaning warning with possible loss of assistance functions

Repair estimate

DifficultyEasyDIY possible
Parts and labour€20–200
Time0.2–1 h

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

Parts involved

sensor cleaning air blower relay arelay control circuitsensor cleaning air blower a

Related codes

B0100B0102B0105

References: hella.com, patents.google.com, eenewseurope.com.