B0040 – Driver Side (Left-Front) Deployment Loop – Resistance Low

What it means

B0040 sets when the SRS/airbag control module detects abnormally low resistance in the driver-side deployment loop. Factory service content (Saab WIS) labels B0040 as “Driver side deployment, resistance low,” aligning with an electrical short/low-ohmic condition in the driver airbag circuit. Saab Wisonline+1

Note: Some aftermarket references map B0040 to other rows/positions (e.g., “third-row left-side airbag”). That reflects platform differences in how B-codes are assigned; always verify against the OEM manual for the specific vehicle. RepairPal.com

Typical symptoms

  • Airbag/SRS warning lamp on; module inhibits that loop until fixed. Saab Wisonline

Severity / priority

High (safety-critical). A loop fault can lead to improper or non-deployment in a crash. Saab Wisonline

Common causes

  • Shorted segment in the driver airbag high/low control circuits (low resistance).
  • Clock spring (spiral cable) damage creating unintended continuity.
  • Connector/terminal issues (backed-out pins, corrosion, shorting-bar problems).
  • Less common: driver airbag module or SRS control unit fault. Saab Wisonline+1

Diagnostic notes

  • Use an SRS-capable scan tool; confirm B0040 and check companion loop codes. Follow OEM SRS safety procedures.
  • Perform visual/circuit checks per the manual; look for short-to-ground/B+ or unintended low resistance across the loop.
  • Flex harness/column while monitoring to expose intermittents; compare measured values to OEM thresholds. Saab Wisonline+1

Possible fixes

  • Repair the harness where a short/low-resistance path is found; correct pin fit/corrosion.
  • Replace a failed clock spring (initialize if required).
  • Replace the driver airbag module only if it fails OEM-directed tests; evaluate SDM/RCM last.
  • Clear DTCs and verify with a re-scan. Saab Wisonline

Primary sources: Saab WIS entries explicitly defining B0040 as “Driver side deployment, resistance low,” including platform-specific DTC lists. Saab Wisonline+2Saab Wisonline+2
Supplemental (platform variance): RepairPal shows a “third-row left-side airbag” mapping—useful to illustrate why OEM lookup is required for the exact vehicle. RepairPal.com