B0029: Right Curtain Deployment Control 1 (Subfault)

The restraints module measures each pyrotechnic firing circuit continuously, passing a current far too small to set anything off and checking that the resistance it sees stays inside a narrow window. Deployment loops are specified tightly because the module has to be able to distinguish a healthy inflator from a corroded terminal, and a few tenths of an ohm is enough to matter. B0029 is stored when the primary right curtain loop falls outside that window — open, shorted to power or to ground, or simply drifted high on resistance. A symptom byte accompanies the code and names which of those it was; read it, because it decides the entire direction of the diagnosis.

The useful thing about loop 1 specifically is that it is the universal one. Every vehicle with a right curtain airbag has this circuit. Loop 2 exists only on designs that fire the curtain through more than one channel, so a stored B0029 needs no architectural investigation before you start work — it is describing hardware you know is there.

That also determines what the code means for the occupant. On a single-loop vehicle, this circuit is the entire right curtain. A fault here does not degrade the airbag; it takes it out. The head protection along the right-hand windows, in a side impact and in a rollover, is what is at stake, and nothing about how the vehicle drives will hint at it.

Where the circuit runs is the other half of the story. The curtain is packed into the roof rail and its firing connector is up at the A-pillar, behind the trim panel that has to come off for a windscreen replacement. Windscreen work is common, is often done quickly and away from a workshop, and involves the one trim panel that sits directly over this connector. A curtain code that appears within days of new glass being fitted is a disturbed or partly seated connector until proven otherwise, and reseating it costs almost nothing compared to what people spend chasing it elsewhere. The same applies to sun visor, grab handle, mirror and roof console work, which all reach into the same area.

The connectors themselves are built to resist accidental firing and that construction is part of the diagnosis. Curtain airbag connectors carry a shorting bar that bridges the two loop conductors whenever the connector is unmated, so the inflator cannot be set off by stray voltage while it sits disconnected. A shorting bar that has been bent or left engaged by a connector that is not fully home makes the loop read as a dead short — which the module reports as a fault, correctly, even though the airbag and the wiring are both perfect. Inspect the mating faces rather than assuming a short means damaged wire.

This is not a job to approach casually. The loop terminates in a pyrotechnic device, and the manufacturer's power-down and wait procedure exists because energy remains in the system for a period after the battery is disconnected. Have it done by a technician with the correct service data and equipment.