Code Definition

B1812 — Lamp Backup Switch Input Circuit Short To Battery

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

About B1812

B1812 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 B1812 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.

B1812 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) monitors an input signal from the backup lamp switch on the transmission to determine when reverse has been selected. DTC B1812 sets when the BCM detects battery voltage on the backup switch input line at a time when the gear selector is in a position other than reverse, indicating that the input wiring or the switch itself has shorted to a battery feed somewhere between the switch contacts and the BCM input pin. Because the BCM uses this input to command the backup lamps, the rear view camera, and the parking aid system, a constant high signal can cause the syste...

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