Airbags

B0042 — Driver Frontal Airbag Deployment Loop Circuit Fault (Stage 2)

Severity: high Drive with care, to a shop

What B0042 means

The SRS control module constantly tests the circuit that fires the stage 2 squib in the frontal airbag, usually the driver's. B0042 sets when the loop is open, shorted to ground or voltage, or its resistance is outside the expected range. On some vehicles the code refers to the third row left frontal stage 2 loop. While it is active, the system may disable that airbag.

Symptoms

  • Airbag (SRS) warning light is on
  • Driver frontal airbag may be disabled and not deploy in a crash
  • Steering wheel buttons such as the horn or audio controls may stop working
  • No other drivability problems

Possible causes

  1. Open circuit or broken wire in the airbag loop
  2. Short to ground or to voltage in the loop
  3. Worn or failed clockspring in the steering column
  4. Faulty squib or airbag module
  5. Corroded or partly seated connectors under the seat or on the steering column
  6. Failed SRS control module (rare)

How to diagnose

  1. Scan all SRS codes with a scan tool that supports airbags, record the data, then clear and see if B0042 returns
  2. Inspect connectors under the steering column and front seats for corrosion, loose locks and bent pins
  3. Ask whether recent work on the wheel, dash or seats left a connector unplugged
  4. Disconnect the battery and wait the manufacturer's specified time before touching the airbag circuit
  5. Check the harness for opens and shorts using the factory wiring diagram, never applying power to the circuit
  6. Measure clockspring resistance and compare it with specification
  7. Test the squib only with the manufacturer's recommended tool, not a standard multimeter
  8. If wiring checks out, test or replace the SRS module

Common fixes

  • Repair damaged wiring or replace the connector
  • Replace the clockspring
  • Replace the airbag module or squib
  • Replace and, if needed, program the SRS control module
  • Clear the code and confirm the SRS light stays off

Questions and answers

What does B0042 mean?

The SRS module found a fault in the stage 2 frontal airbag circuit. The airbag may not deploy in a crash until it is fixed.

Can I replace the clockspring or airbag myself?

It is risky because accidental deployment can cause injury. Disconnect the battery, wait the specified time and follow the manufacturer's procedure. If unsure, use a professional shop.

Why did the SRS light come on after steering wheel work?

Most often an airbag or clockspring connector was left unplugged or a wire was damaged. Check the connectors, then read and clear the code.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.