← View Generic B0421 Guide Severity: Medium
🚗 Vehicle-Specific Guide

This guide is customized for your 2020 Chevrolet SILVERADO 1500 PICKUP

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

on 2020 Chevrolet SILVERADO 1500 PICKUP

Fix Cost
$50 - $200
Parts & Labor
Difficulty
3/5
1-2 hours
DIY Possible?
✅ Yes
Save money
Your Vehicle
2020 Chevrolet
SILVERADO 1500 PICKUP
⚠️

Important for 2020 Chevrolet SILVERADO 1500 PICKUP Owners

Before starting repairs, verify which engine your 2020 Chevrolet SILVERADO 1500 PICKUP has. Check your VIN or engine code to ensure you order the correct parts.

📖 What Does B0421 Mean on 2020 Chevrolet SILVERADO 1500 PICKUP?

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
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How to Fix B0421 on 2020 Chevrolet SILVERADO 1500 PICKUP

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.

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Parts for 2020 Chevrolet SILVERADO 1500 PICKUP

BCM Shop ↗ fuses Shop ↗ wiring harness Shop ↗ exterior light bulbs Shop ↗

Essential Tool

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OBD2 Scanner

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Related Diagnostic Codes

Other codes that may appear with B0421

B0419 Sequential Code

B0419: Power Window Relay Circuit Malfunction

Medium
B0420 Sequential Code

B0420: Seat Switch Circuit Malfunction

Medium
B0422 Sequential Code

B0422: Body Control Module (BCM) Security System Malfunction

Medium
B0423 Sequential Code

B0423: Audio System Malfunction

Medium

💡 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