B0121
Serious Severity (Level 4)Fluid Reservoir Level Sensor F
B0121 usually means fluid Reservoir Level Sensor F.
Can you still drive with B0121?
⚠️Limited driving — get to a repair shop within 1–2 days. Avoid long trips and highway speeds.
Typical repair cost: $100 – $2000
Severity Level 4 — Serious
This code indicates a serious issue that can cause noticeable driveability problems and potential engine damage if not addressed. The vehicle should be taken to a mechanic as soon as possible. Extended driving is not recommended.
Common Symptoms
- Airbag/SRS warning light on — airbags may be disabled
- Check Engine Light illuminated
- Seat belt pretensioner may not deploy in a collision
- Diagnostic trouble code (DTC) stored in module memory
Possible Causes
- Faulty airbag module or impact sensor — most common cause, test before replacing
- Damaged or corroded wiring/connector in the airbag/SRS (supplemental restraint) system circuit
- Blown fuse or faulty relay for the airbag/SRS (supplemental restraint) system
- Poor ground connection — check and clean all related ground points
- Control module fault — rare but possible, only consider after ruling out simpler causes
Common Fixes
- Scan vehicle with a professional-grade OBD2 scanner to read all stored codes and freeze frame data — note the conditions when the code set ($29-120 at shop, free at auto parts store for basic scan)
- Visually inspect the airbag/SRS (supplemental restraint) system wiring harness and connectors — look for chafed wires, melted insulation, green corrosion, loose pins, or rodent damage (often free to check yourself, $63 diagnostic fee at shop)
- WARNING: Airbag/SRS system work should be performed by a qualified professional. Disconnect battery for 15+ minutes before any SRS work. Replace faulty component and clear SRS codes with professional tool ($354-618 at qualified shop)
- Replace airbag module or impact sensor if testing confirms it has failed — use OEM quality, avoid the cheapest no-name aftermarket parts that fail in a year ($100-2000)
- Check and replace any blown fuses in the airbag/SRS (supplemental restraint) system fuse circuit — if fuse blows again, there's still a short that needs to be found ($4-10 for fuses)
Estimated Repair Cost
These are estimated costs based on generic repair data. Actual costs may vary depending on your vehicle, location, and labor rates.
Frequently Asked Questions
What does B0121 mean?
B0121 stands for "Fluid Reservoir Level Sensor F". B0121 usually means fluid Reservoir Level Sensor F.
Can you drive with B0121?
Limited driving — get to a repair shop within 1–2 days. Avoid long trips and highway speeds.
How much does it cost to fix B0121?
Repair costs for B0121 typically range from $100 to $2000, depending on your vehicle make, model, and local labor rates. Common fixes include: Scan vehicle with a professional-grade OBD2 scanner to read all stored codes and freeze frame data — note the conditions when the code set ($29-120 at shop, free at auto parts store for basic scan); Visually inspect the airbag/SRS (supplemental restraint) system wiring harness and connectors — look for chafed wires, melted insulation, green corrosion, loose pins, or rodent damage (often free to check yourself, $63 diagnostic fee at shop); WARNING: Airbag/SRS system work should be performed by a qualified professional. Disconnect battery for 15+ minutes before any SRS work. Replace faulty component and clear SRS codes with professional tool ($354-618 at qualified shop).
Will B0121 clear itself?
Explore Repair Costs
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