Code Definition

B0040 — LHF seatbelt deployment loop Circuit resistance low

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

About B0040

B0040 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 B0040 is stored, the module has detected a signal or supply voltage lower 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 B0040 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

This fault code is set when the Restraints Control Module (RCM) detects that the resistance in the left hand front (LHF) seatbelt pretensioner deployment circuit is lower than the expected range. The RCM continuously monitors the pretensioner deployment loop resistance to confirm the circuit is intact and ready to fire in a collision. Low resistance usually indicates a short circuit or a partial short between the deployment wires, which can compromise correct pretensioner operation and, in a fault condition, risks unintended activation. When this code is set the airbag or SRS warning lamp is i...

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