Code Definition

B1509 — Flash To Pass Switch Circuit Short To Battery

System: Body  |  Type: Manufacturer-Specific  |  Make: Generic

About B1509

B1509 is a manufacturer-specific body diagnostic trouble code. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

When B1509 is stored, the module has detected a short-circuit (voltage pulled to ground or to supply) in the monitored circuit.

Scanning & clearing: Body (B) codes are often stored in the body control module, airbag module, or climate module. A basic OBD-II tool usually will not read body codes — an enhanced or OEM-level scan tool is typically required.

B1509 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The Body Control Module (BCM) or headlamp control module monitors the flash to pass switch input from the multifunction stalk and expects it to sit at a defined idle voltage when the switch is open. DTC B1509 sets when the module sees battery voltage on the flash to pass switch input wire continuously, indicating a short to a constant or accessory 12V source somewhere along the input circuit. Because the input appears permanently active to the module, the high beams may flash continuously, stay illuminated, or trigger erratically, and on some vehicles the flash to pass function may be locked o...

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