B0021 is GM's code for the passenger seat side airbag deployment loop, the circuit that fires the thorax bag built into the outboard bolster of the front passenger seat. Because the whole circuit lives under a seat that slides, tilts, and reclines, the harness takes abuse that a fixed harness never sees. That is where this code usually comes from.
GM's descriptors read Passenger Seat Side Air Bag Deployment Loop, with 01 for short to battery, 02 for short to ground, 04 for open, 0D for high resistance, and 0E for low resistance. On a 2013 crossover the SDM sets the code when loop resistance runs above 4.2 ohms or below 1.4 ohms for 2 seconds. B0014 is the identical code for the driver seat.
GM's own diagnostic aid for these two codes is worth repeating: run the seat through its full travel while watching the deployment loop parameters on a scan tool. Stress and damage to the harness from seat movement is a known cause, and a wire that only opens at the end of its travel will not show up with the seat parked in one spot.
One thing this code is not: it has nothing to do with the passenger presence system or the weight sensor in the seat cushion. Those set their own codes in the B0074 family. People replace occupant sensors over B0021 and end up back where they started.
Circuit. The SDM is reporting the electrical state of the seat airbag loop. It is not a crash record, and GM notes the module will still attempt deployments with this code stored. That said, a seat airbag that already fired reads open forever, so on a vehicle with side impact damage expect this code beside a locked module and other side system codes.
No. Nothing about clearing module memory changes a damaged wire under the seat, and B0021 returns on the next start. Repair or replace the harness and connector first. If the seat airbag itself deployed, it needs a matching seat airbag before anything else, and then the module that recorded the deployment needs an airbag module reset to come out of its locked state.
The passenger seat side wording is GM SIR language and appears on Chevrolet, GMC, Buick, Cadillac, and Pontiac vehicles from the mid 2000s through the mid 2010s, from the Silverado and Sierra to the Terrain, Equinox, and Traverse. Other manufacturers use B0021 for their own restraint circuits, so tie the code to the module that reported it before ordering parts.
Get the seat all the way back, look under it, and follow the harness from the floor connector to the seat frame. Check for a connector that was never relatched, a wire routed over a sharp bracket, and a CPA clip that is only half in. Then cycle the seat through its travel with the scan tool on the loop data.
If B0020, B0014, or a roof rail code is stored at the same time, look upstream at the SDM connector or the inline harness instead of at one seat.
Related codes: B0016, B0028, B0020
Keep reading:
Code scope: Chevrolet, GMC, Cadillac, Buick. The same number can mean something different on another manufacturer, so match the code to your make before you act on it.
A reset clears stored crash data. A replacement part fixes a hardware fault. We have read these codes since the nineties and will tell you which one you are looking at.
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