Code Definition

B1803 — Lamp Turn Signal Rear Output Circuit Open

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

About B1803

B1803 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 B1803 is stored, the module has detected an open (broken or disconnected) electrical path 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.

B1803 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 circuit for proper current flow when the lamp is commanded on. DTC B1803 sets when the BCM detects an open circuit specifically on the rear turn signal output, meaning current cannot flow through the load when the lamp is commanded by the turn signal stalk or hazard switch. The rear turn signal circuit routes through the C pillar and across the trunk hinge or tailgate where the harness is exposed to repeated flexing every time the lid is opened, making broken conductors at flex points the dominant failure ...

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