Body, generic

B0121 Fluid Reservoir Level Sensor F

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

B0121 closes the row with level sensor F. Small local reservoirs are one reason a vehicle might carry six level sensors: Ford's application DE102018109892A1 describes a camera washer with its own container close to the lens, fitted with a buoyant level sensor that signals when the fluid has fallen to a set low point and the container needs topping up. How the result reaches the driver is a separate design question; Mannesmann VDO's patent US6588270B1 even moved the washer level display next to the fuel filler neck so that it is noticed while refuelling. No manufacturer publishes which reservoir F stands for or documents B0121. Driving is not affected, but the washer it watches may run dry unnoticed.

Likely causes

Float of sensor F stuck by deposits or ice
Wiring to the small reservoir chafed or connector corroded
Level sensor F defective

Symptoms

  • Missing or permanent refill message for the affected reservoir
  • Washer served by this reservoir runs dry without warning

Repair estimate

DifficultyMediumDIY possible
Parts and labour€20–200
Time0.3–2 h

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

Parts involved

fluid reservoir level sensor fsensor wiring

Related codes

B011CB011DB011EB011FB0120

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