OBD Guide
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B21F8

Exterior Lighting Power Supply Input 1 Circuit Open

B21F8 is an OBD-II diagnostic trouble code meaning: Exterior Lighting Power Supply Input 1 Circuit Open. Common causes: break in the wiring harness, light relay fault. Estimated repair cost: $22–167.

Severity
⚠️ Medium
Can you drive?
Do not drive — repair immediately
Approx. repair cost
$22–167 (est.)

Symptoms

  • Headlights don't work
  • Side lights don't work
  • Exterior light flashing
  • Error message on the dashboard

Causes

  • Break in the wiring harness
  • Light relay fault
  • Blown fuse
  • Problem with the lighting control unit
  • Short circuit in the circuit

How to Fix

  1. Check external lighting fuses
  2. Check lighting relay
  3. Inspect the wiring harness for damage
  4. Check the voltage in the power circuit
  5. Replace damaged components if necessary
  6. Reflash the lighting control unit (if required)

Related codes

B21F7B21F9B2100

FAQ

What does the B21F8 code mean?

B21F8 is an OBD-II diagnostic trouble code that indicates: Exterior Lighting Power Supply Input 1 Circuit Open

What causes a B21F8 error code?

The most common causes of B21F8 include: Break in the wiring harness; Light relay fault; Blown fuse; Problem with the lighting control unit.

How do I fix a B21F8 diagnostic trouble code?

To fix B21F8: Check external lighting fuses. Check lighting relay. Inspect the wiring harness for damage. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with B21F8?

Do not drive — repair immediately

How much does it cost to fix B21F8?

The estimated repair cost for B21F8 is $22–167. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat