← Back to Search Severity: Medium

B0421

B0421: Body Control Module (BCM) Malfunction - Exterior Lighting

Fix Cost

$50 - $200

Parts & Labor

Difficulty

3/5

Moderate

1-2 hours

DIY Possible?

✅ Yes

Save money

📖 What Does B0421 Mean?

The Body Control Module (BCM) has detected a malfunction in the exterior lighting system, which may cause issues with the headlights, taillights, or other exterior lights.

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Symptoms

• Dim or inoperative exterior lights
• faulty headlight aim
• or erratic lighting behavior

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Common Causes

• Faulty BCM
• wiring issues
• blown fuse
• or damaged exterior light bulbs

Fix Guide

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Possible Solutions

1. Check and replace blown fuses. 2. Inspect and repair or replace wiring as needed. 3. Test and replace the BCM if necessary. 4. Replace faulty exterior light bulbs.

❓ Common Questions About B0421

Can I drive with code B0421?

You can drive for a short time, but should address code B0421 soon to avoid worsening the problem or failing an emissions test.

How much does it cost to fix code B0421?

The estimated repair cost for code B0421 is between $50 and $200. This includes parts and labor. Prices may vary based on your vehicle's make and model.

Is code B0421 easy to fix myself?

This repair is considered moderate. It may require specialized tools or significant disassembly. If you are not an experienced mechanic, professional help is recommended.

Required Parts

Tools

multimeter wire tester screwdrivers torx bits

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Need a Pro?

Complex codes like B0421 can be tricky. Don't risk it if you're unsure.

Quick Stats

Severity Medium

DIY Friendly Yes

Est. Time 1-2 hours

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Related Diagnostic Codes

Other codes that may appear with B0421

B0419 Sequential Code

💡 Why These Codes Are Related:

• Similar Issues: Same root cause or component failure
• Related Problems: Often occur together due to system interactions
• Sequential Codes: Progressive failure stages or multiple sensors
• Same System: Components within the same automotive system