B3A21
Serious Severity (Level 4)Active Aerodynamic Feature Control Module B
B3A21 usually means active Aerodynamic Feature Control Module B.
Can you still drive with B3A21?
⚠️Limited driving — get to a repair shop within 1–2 days. Avoid long trips and highway speeds.
Typical repair cost: $150 – $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
- Check Engine Light illuminated
- The engine/body control module is not operating as designed
- Warning light or malfunction indicator related to the engine/body control module is illuminated
- Diagnostic trouble code (DTC) stored in module memory
Possible Causes
- Faulty control module — most common cause, test before replacing
- Damaged or corroded wiring/connector in the engine/body control module circuit
- Blown fuse or faulty relay for the engine/body control module
- 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 ($45-110 at shop, free at auto parts store for basic scan)
- Visually inspect the engine/body control module wiring harness and connectors — look for chafed wires, melted insulation, green corrosion, loose pins, or rodent damage (often free to check yourself, $135 diagnostic fee at shop)
- Replace control module if testing confirms it has failed — use OEM quality, avoid the cheapest no-name aftermarket parts that fail in a year ($150-2000)
- Check and replace any blown fuses in the engine/body control module fuse circuit — if fuse blows again, there's still a short that needs to be found ($3-17 for fuses)
- Perform a wiggle test on the engine/body control module wiring harness while monitoring live data — see if the fault returns when you move the harness at different points ($0-142 diagnostic labor)
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 B3A21 mean?
B3A21 stands for "Active Aerodynamic Feature Control Module B". B3A21 usually means active Aerodynamic Feature Control Module B.
Can you drive with B3A21?
Limited driving — get to a repair shop within 1–2 days. Avoid long trips and highway speeds.
How much does it cost to fix B3A21?
Repair costs for B3A21 typically range from $150 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 ($45-110 at shop, free at auto parts store for basic scan); Visually inspect the engine/body control module wiring harness and connectors — look for chafed wires, melted insulation, green corrosion, loose pins, or rodent damage (often free to check yourself, $135 diagnostic fee at shop); Replace control module if testing confirms it has failed — use OEM quality, avoid the cheapest no-name aftermarket parts that fail in a year ($150-2000).
Will B3A21 clear itself?
Explore Repair Costs
Related OBD-II Codes
These codes are in the same range as B3A21 and often share similar causes and fixes.
Worried about repair costs?
Get transparent estimates and verify your mechanic's quote before authorizing repairs.
Related Discussions
See what other car owners are saying about this code and related repairs.
View B3A21 discussions in the community