What are the common causes of B0021?

An open in the left curtain stage 1 squib circuit. A short to ground on the left curtain wiring. Damage at the left curtain connector, often after roof or trim work. A failed left curtain airbag module. A left curtain stage 1 output fault in the airbag control module.

Inspect the left curtain stage 1 squib wiring for opens and shorts. Check the left curtain connector for damage after trim work. Measure left curtain stage 1 resistance through the harness. Replace the left curtain airbag if the circuit tests open. Replace the airbag control module if the curtain output is faulty. Clear the code and retest.

B0021

Left Curtain Deployment Control 1

System: Body control (B code)
Lamp: Airbag Light
Category: Body

What it means

B0021 means Left Curtain Deployment Control 1.

Check these first

An open in the left curtain stage 1 squib circuit
A short to ground on the left curtain wiring
Damage at the left curtain connector, often after roof or trim work
A failed left curtain airbag module
A left curtain stage 1 output fault in the airbag control module

What to do next

Inspect the left curtain stage 1 squib wiring for opens and shorts
Check the left curtain connector for damage after trim work
Measure left curtain stage 1 resistance through the harness
Replace the left curtain airbag if the circuit tests open
Replace the airbag control module if the curtain output is faulty
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.