Serious — S4BMW 3 Series · european tier
B0021 on BMW 3 Series
The B0021 diagnostic trouble code on a BMW 3 Series indicates left curtain deployment control 1. For BMW vehicles, this code is commonly triggered by faulty airbag module — most common cause, test before replacing or damaged or corroded wiring/connector in the airbag/srs (supplemental restraint) system circuit.
Can You Still Drive?
Drive to a shop soon. Risk of damage if ignored.
Estimated Repair Cost
$100 – $2,000
for BMW 3 Series
Common on This Vehicle?
The B0021 code is relatively common on BMW vehicles and often appears alongside other diagnostic codes.
Symptoms on BMW 3 Series
- •Check Engine Light illuminated
- •Airbag/SRS warning light on — airbags may be disabled
- •Seat belt pretensioner may not deploy in a collision
- •Diagnostic trouble code (DTC) stored in module memory
Common Causes
- •Faulty airbag module — 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