B0021 code meaning
Left Curtain Deployment Control 1
What B0021 means
In the J2012 order B0021 is the first firing loop of the left curtain airbag, the bag that drops from the roof rail over the side windows. Mitsubishi files it under the left curtain module and stores byte 11, 12, 13 or a short to another circuit once the condition has lasted 2 seconds. Mercedes-Benz reads B002113 as an open squib of the left window bag on the A-Class, CLA and GLB, where raised contact resistance at the restraint unit plug was the cause (LI54.21-P-070658). Curtain 1 is the only or front curtain inflator; B0022 is the second one. GM Global A modules use B0021 for the passenger seat side airbag instead, with bulletins on seat harness contact (PI1469, 23-NA-030). Airbag lamp on; the left curtain may not fire.
B0021 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyWorkshop only
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of B0021
- Airbag warning lamp on
- Left curtain airbag may not deploy in a side impact or rollover
- Safety note: do not probe the airbag circuit yourself; unplug airbag connectors only with the battery disconnected and the stated wait time observed
Common causes of B0021
- Most likelyRaised contact resistance at the curtain airbag or restraint module connector
- PossibleDamaged lead along the A-, B- or C-pillar or the roof rail
- PossibleInternal fault in the left curtain airbag module
- Less likelyFault or unsuitable software in the restraint control module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Left curtain airbagSRS roof wiringSRS control module
What each part of B0021 means
| B | Body system: airbags, seat belts, power seats, lights and climate control. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 21 | The exact fault in that area. |
What to do next
- Note B0021 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about B0021
What does B0021 mean?
B0021 means "Left Curtain Deployment Control 1". In the J2012 order B0021 is the first firing loop of the left curtain airbag, the bag that drops from the roof rail over the side windows. It is a generic code, so it means the same on every make.
Is it safe to drive with B0021?
B0021 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will B0021 fail an emissions test?
B0021 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is B0021 to fix?
Difficulty: workshop only. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will B0021 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.