OBD Guide
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B2509

Rear Fog Lamp Switch Circuit Failure

B2509 is an OBD-II diagnostic trouble code meaning: Rear Fog Lamp Switch Circuit Failure. Common causes: open or short circuit in wiring harness, oxidation of switch contacts or connectors. Estimated repair cost: $6–56.

Severity
✅ Low
Can you drive?
Limited driving only, diagnose soon
Approx. repair cost
$6–56 (est.)

Symptoms

  • Rear fog light does not turn on
  • The malfunction indicator on the dashboard is on
  • The flashlight may be unstable (blinking)

Causes

  • Open or short circuit in wiring harness
  • Oxidation of switch contacts or connectors
  • Blown circuit fuse
  • Fog lamp relay malfunction
  • Problems with the switch on the instrument panel
  • BCM malfunction (rare)

How to Fix

  1. Check and replace circuit fuse if necessary
  2. Inspect the wiring harness for damage
  3. Clean the contacts of the switch and connectors
  4. Check the functionality of the switch with a multimeter
  5. Test the fog light relay
  6. If necessary, diagnose the BCM

Related codes

B2512B2513B2514

FAQ

What does the B2509 code mean?

B2509 is an OBD-II diagnostic trouble code that indicates: Rear Fog Lamp Switch Circuit Failure

What causes a B2509 error code?

The most common causes of B2509 include: Open or short circuit in wiring harness; Oxidation of switch contacts or connectors; Blown circuit fuse; Fog lamp relay malfunction.

How do I fix a B2509 diagnostic trouble code?

To fix B2509: Check and replace circuit fuse if necessary. Inspect the wiring harness for damage. Clean the contacts of the switch and connectors. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with B2509?

Limited driving only, diagnose soon

How much does it cost to fix B2509?

The estimated repair cost for B2509 is $6–56. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat