fault code guide
B0100: Side Airbag Deployment Control Circuit Malfunction
Fault code B0100 means the car detected an electrical problem in a side airbag circuit. The side airbag will not deploy properly in an impact, putting you at risk.
How it shows up: The red or amber airbag (SRS) warning light stays lit on your instrument cluster after starting the engine. You will not notice any change in how the car drives, and the B0100 code must be read using an OBD diagnostic scanner.
Updated 9 November 2026
Can I keep driving?
Service soon
The car drives normally, but the side airbag is disabled and will not protect you during a collision.
What to do right now
- 1Check whether the airbag warning light remains illuminated steadily on the instrument cluster.
- 2Avoid storing bags, bottles, or other loose items beneath the front seats.
- 3Book an appointment with a qualified mechanic or auto electrician to inspect the restraint system.
Likely causes
Most likely first.
- Likely
Loose or damaged under-seat wiring connector
Moving the front seats backwards and forwards can pull, loosen, or strain the yellow airbag wiring harness connectors underneath.
- Possible
Corroded connector terminals
Moisture or damp carpets inside the cabin can oxidise the metal pins inside the under-seat harness plug, increasing electrical resistance.
- Rare
Damaged side airbag squib or module
Internal wear or an open circuit within the side impact airbag module itself triggers a deployment circuit malfunction.
- Rare
Faulty SRS airbag control module
Internal electronic component failure in the central restraint control unit can prevent it from monitoring or firing the circuit correctly.
What you can check yourself
Park somewhere safe and level, engine off, before you start.
- 1
Check under the front seats
Park safely, switch off the ignition, and remove the key. Look under the front seats to see if loose objects, water bottles, or luggage have jammed or disturbed the wiring.
- 2
Look for visible wire damage
Use a torch to look at the bright yellow harness sheathing beneath the seats. Check for obvious signs of chafing, pinched wires, or completely detached plugs without pulling on any cables.
- 3
Inspect the footwells for dampness
Feel the carpet beneath both front seats for dampness or pooling water. Water ingress from blocked drainage channels can corrode electrical connections and trigger circuit faults.
Rough cost to fix
Rough estimateTypical prices in Ireland (€) and the UK (£), from an independent garage up to a main dealer. The total cost depends mainly on whether the fault is a loose connector contact or requires a replacement side airbag module.
Under-seat wiring harness repair or connector cleaning
- Do it yourself
- Garage job
- At a garage
- €90–180£75–150 in the UK
Side airbag wiring loom replacement
- Do it yourself
- Garage job
- At a garage
- €180–380£150–320 in the UK
Side airbag unit replacement
- Do it yourself
- Garage job
- At a garage
- €350–750£300–650 in the UK
When to go to a garage
- The airbag warning light remains illuminated after checking for loose under-seat items.
- You find damp carpets or signs of water damage around the seat connectors.
- You want the restraint system safely tested, as working on live airbag circuits risks accidental deployment.
Questions drivers ask
Can I still drive my car with code B0100?
Yes, the car will drive normally because the engine, brakes, and steering are unaffected. However, the side airbag system is disabled while the warning light is lit, which leaves occupants unprotected during a side collision.
Will code B0100 cause an MOT or NCT failure?
Yes, an illuminated airbag warning lamp is an automatic fail on both the UK MOT and the Irish NCT. The light must illuminate during the initial ignition bulb check and turn off shortly after the engine starts.
Can I fix the under-seat connector myself?
Working on airbag wiring is not recommended for home mechanics due to the risk of accidental deployment. Airbag modules contain pyrotechnic charges, so the 12-volt battery must be disconnected and the system completely discharged before any connectors are handled.
Will clearing the fault code with an OBD scanner turn the light off?
Clearing the code will only turn off the light if the underlying wiring or module problem has already been rectified. If high electrical resistance or a broken connection remains, the restraint module will immediately detect the fault and turn the light back on.
Test rules here are for the National Car Test in Ireland (NCT) and the MOT in the UK. Elsewhere, check the regulations of your own country or state before going for a vehicle test.
The warning light you may see
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General guidance for most cars, not a diagnosis of yours. Details differ by make, model and year - check your handbook, and if in doubt, don't drive.