B0042 OBD2 Code Guide
B0042 is a body / srs diagnostic trouble code. Use this hub to understand the plain meaning, the first checks to run, and which vehicle-specific guides may be more useful before replacing parts.
Third Row Left Side Airbag Deployment Loop Fault
Code B0042 indicates a detected fault within the deployment circuit for the third-row left side airbag. This means the Supplemental Restraint System (SRS) control module has identified an open circuit, short circuit, or incorrect resistance within the wiring, connectors, or the airbag inflator itself, preventing proper deployment in the event of a collision. This compromises the vehicle's occupant safety system, potentially leading to non-deployment or, in rare cases, inadvertent deployment.
Code verification standard
B0042 is published with SAE J2012 / ISO 15031-6 code structure plus OBD2 B0042 diagnostic context.
First checks
- - Read all stored and pending codes before clearing anything.
- - Save freeze-frame data so you know speed, load and temperature when the code set.
- - Inspect wiring, connectors, fuses, hoses and obvious leaks tied to the named system.
- - Compare live data against realistic values before buying sensors or modules.
- - Clear the code only after repair and complete a drive cycle to confirm it does not return.
B0042 diagnostic path
- 11. Scan and Verify: Use an advanced scan tool capable of accessing the SRS module to confirm the B0042 code and check for any related or accompanying SRS codes. Record freeze frame data for further analysis.
- 22. Visual Inspection: Disconnect the battery and wait at least 10-15 minutes to allow the SRS system to fully discharge. Carefully inspect the wiring harness, connectors, and the third-row left side airbag module itself for any signs of damage, corrosion, loose connections, or previous repairs. Pay close attention to areas where wiring might be pinched, abraded, or exposed.
- 33. Circuit Resistance Test: With the battery still disconnected, carefully disconnect the airbag module connector. Using a multimeter, measure the resistance across the airbag deployment loop terminals at the SRS module connector (refer to vehicle-specific wiring diagrams for pinouts). Compare this reading to the manufacturer's specified resistance range. An open circuit (OL), short circuit (0 ohms), or out-of-range resistance indicates a fault in the wiring or the airbag inflator. *Never probe the airbag module directly without a dummy resistor, as this can cause inadvertent deployment.*
- 44. Power and Ground Check (SRS Module): If the circuit resistance appears correct, verify proper power and ground supply to the SRS control module according to the vehicle's wiring diagram. Ensure all fuses related to the SRS system are intact and receiving power.
- 55. Component Isolation and Testing: If the resistance test points to the airbag or wiring, isolate the components. If the wiring is confirmed good through continuity and resistance checks, the airbag module itself is likely faulty. If the wiring is damaged, repair or replace the affected harness section using appropriate SRS-rated repair procedures and materials.
Verify before repair
- - Repair or replace damaged wiring and/or corroded connectors leading to the third-row left side airbag module.
- - Replace the faulty third-row left side airbag module (inflator assembly) if internal resistance is out of specification.
- - Replace the SRS control module if all other components and wiring test good, and the module is determined to be internally faulty (less common for this specific code, but possible).
Vehicle-specific pages to check next
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