B0020 B0xxx · Body (B) High severity
Left Side Airbag Deployment Control
Fault in the left-side airbag or curtain deployment loop. Usually the connector under the seat or in the door pillar.
Severity guidance: High — stop driving and diagnose now; risk of further damage
Symptoms you will notice
- Airbag lamp on
- Side impact protection disabled
Common causes
Ordered from most to least likely — start at the top.
- 1 Connector under the seat disturbed or corroded
- 2 Open wiring in the door-pillar harness
- 3 Faulty side airbag unit
- 4 Water ingress
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Disconnect and wait per the safety procedure before touching connectors.
- ✓ Inspect the seat harness connector first — seat movement is a common cause.
- ✓ Read loop resistance from the airbag module.
- ✓ Check for water ingress in the footwell or pillar.
Repair options
- Re-seat or repair the seat connector
- Repair the pillar wiring
- Replace the side airbag unit
B0020 — frequently asked questions
It started after I moved the seat — why? +
The connector under the seat is strain-limited. Moving the seat fully forward or back can pull it loose.
Is a side airbag cheaper to fix? +
Usually, because the fault is nearly always the connector rather than the airbag itself.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.