Code Definition

B1804 — Lamp Turn Signal Rear Output Circuit Short To Battery

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

About B1804

B1804 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 B1804 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.

B1804 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) controls the rear turn signal lamp output and monitors the voltage state on the controlled side of the driver when the lamp is commanded off. DTC B1804 sets when the BCM detects battery voltage on the rear turn signal output line at a time when that line should be at 0V or floating between flash pulses, indicating that the wiring or load has shorted to a battery feed somewhere between the BCM driver and the lamp ground. The rear lamp typically shares its housing with the brake or tail lamp, and the most common cause of this code on combination tail lamps is a corr...

Join TaT to view the complete code information and diagnostic details.

Quick Facts