Low resistance is the complaint behind B102C. The Mercedes restraint control unit measured the driver emergency tensioning retractor squib circuit and found the value below the range it will accept.
Every squib circuit has a resistance window. Too high or open tells the module the path is broken. Too low tells it current is finding a shortcut. B102C is the low reading on the driver tensioning retractor, so the module is seeing less resistance than the igniter alone should present, which usually means conductors are touching somewhere they should not.
That shortcut can be between the two circuit wires, from one wire to ground, or inside the igniter itself. It can also be intermittent, showing up only when the seat is at a certain position or when the harness is wet. A low reading is a different search than an open, because you are hunting for contact rather than for a break.
B102C tracks a live resistance value, which is what puts it in the circuit family. It reflects the wiring at this moment and clears when the reading returns to range. Crash data does not behave that way at all. It records a past event, stays in memory permanently, and requires a module reset rather than any electrical repair.
There is nothing a reset can do about a short. The module measures the same low value on the next key cycle and stores the code again. Locate the contact point, repair or replace the damaged section, and verify the resistance is back in range. A mail in reset applies only if that module is also holding crash data from a deployment.
Mercedes-Benz uses B102C for the driver side tensioning retractor resistance low condition. The companion code for an open or general ignition circuit fault on the same component is a separate number, so read the full code set before deciding what you are chasing.
Disconnect the retractor and measure the harness on its own, because that one step tells you immediately whether the short is in the wiring or inside the igniter. If the harness is clear, the retractor is the part at fault. If the harness still reads low, follow it along the sill and under the seat looking for rub marks, crush points, and moisture. We stock genuine OEM Mercedes seat belts and can help identify the correct assembly at 501-988-0611. Related codes: B1028, B1034, 34-1X.
Trace the wiring and connectors first. If the module still holds the fault after the repair, mail it to us and we will clear it.
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