OBD Guide
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B21F9

Exterior Lighting Power Supply Input 2 Circuit Open

B21F9 is an OBD-II diagnostic trouble code meaning: Exterior Lighting Power Supply Input 2 Circuit Open. Common causes: broken wire in the harness, oxidation of contacts. Estimated repair cost: $22–111.

Severity
⚠️ Medium
Can you drive?
Do not drive — repair immediately
Approx. repair cost
$22–111 (est.)

Symptoms

  • Tail lights don't work
  • No license plate light
  • The lighting fault indicator is on
  • Error message on the dashboard

Causes

  • Broken wire in the harness
  • Oxidation of contacts
  • Blown fuse
  • Faulty lighting relay
  • Problems with the control module
  • Corrosion of connectors

How to Fix

  1. Check the condition of the fuses of the corresponding circuit
  2. Inspect the wiring harness for damage
  3. Check the integrity of the power circuit with a multimeter
  4. Clean connector contacts from oxides
  5. Check the operation of the lighting relay
  6. Test the lighting control module

Related codes

B21F8B2100B21FA

FAQ

What does the B21F9 code mean?

B21F9 is an OBD-II diagnostic trouble code that indicates: Exterior Lighting Power Supply Input 2 Circuit Open

What causes a B21F9 error code?

The most common causes of B21F9 include: Broken wire in the harness; Oxidation of contacts; Blown fuse; Faulty lighting relay.

How do I fix a B21F9 diagnostic trouble code?

To fix B21F9: Check the condition of the fuses of the corresponding circuit. Inspect the wiring harness for damage. Check the integrity of the power circuit with a multimeter. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with B21F9?

Do not drive — repair immediately

How much does it cost to fix B21F9?

The estimated repair cost for B21F9 is $22–111. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat