B0020

Symptoms

• SRS/airbag warning light stays on
• the affected airbag (left-side or passenger instrument panel loop, depending on make) is disabled and will not deploy in a crash while the code is active.

Probable causes

• 1) Wiring open or short in the airbag deployment loop. 2) Corroded
• loose
• or damaged SRS connectors - on GM
• a loose
• damaged
• or missing Connector Position Assurance (CPA) retainer on the yellow airbag connectors is a documented known issue (GM TSB #08-09-41-002H). 3) Moisture/liquid intrusion under the seats corroding connector pins. 4) Faulty clock spring when the fault is in the driver's front airbag circuit. 5) Internal airbag/SRS module failure.

Diagnostic steps

1. SAFETY FIRST: disconnect the negative battery terminal and wait for the SRS capacitors to discharge (sources cite 15 minutes) before touching any yellow SRS connector.
2. Read the exact sub-code (e.g. open circuit vs low resistance/short) with a scan tool that accesses the SRS module - it tells you what kind of electrical fault to hunt.
3. Visually inspect the deployment-loop wiring and yellow SRS connectors (under seats, door jambs, around the steering column) for corrosion, backed-out pins, broken locks, and on GM check the CPA retainers on the airbag connectors.
4. If the circuit points to the driver's front airbag, test the clock spring with a multimeter; a clock spring fault is likely if horn/steering-wheel controls fail at the same time as the airbag light.
5. With a scan tool graphing live resistance data on the circuit, wiggle-test the harness at common failure points - a resistance spike pinpoints the fault location.
6. To isolate module vs loop: with battery disconnected, substitute the deployment loop with an SRS test resistor (sources cite 2.0-3.3 ohm) at the harness, reconnect and rescan - if the code goes away the fault is downstream in the loop/airbag unit; if it stays, suspect wiring to the module or the module itself.
7. Repair the wiring/connector or replace the faulty component, clear codes, and verify the SRS light goes out.