Code Definition

B2520 — High Mount Stop Lamp Circuit Short to Battery

System: Body  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About B2520

B2520 is a generic (obd-ii standard) body diagnostic trouble code. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

When B2520 is stored, the module has detected a short-circuit (voltage pulled to ground or to supply) in the monitored circuit; and a signal or supply voltage higher than the expected operating range.

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.

Because B2520 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The Body Control Module (BCM) monitors the high mount stop lamp (CHMSL) control circuit and expects 0V on the output wire when the lamp is commanded off. DTC B2520 is set when the BCM detects battery voltage on the CHMSL feed wire while the lamp should be inactive, indicating an unintended source of power on the circuit. This typically occurs when the feed wire is chafed against a constant or switched battery feed, when aftermarket accessories are improperly spliced into the brake light wiring, or when internal damage to the CHMSL assembly creates a back-feed condition. Drivers may notice the ...

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