B1025 is Mercedes-Benz's code for too much resistance in the driver airbag firing circuit. The factory text reads that the ignition circuit with component R12/13, driver airbag ignition squib 1, is above its allowed resistance. R12/13 is the first stage igniter inside the driver airbag, and the circuit that feeds it runs from the restraint systems control unit up the steering column and across the contact reel.
Mercedes calls the airbag module N2/7, the restraint systems control unit, and on most models it is bolted to the tunnel under the center console. Every time the ignition comes on, N2/7 puts a small current through each firing loop and measures what comes back. A healthy squib reads a couple of ohms, so a poor connection anywhere in that short path stands out immediately.
B1025 is the high half of a matched pair. B1024 is the same circuit reading too low. That pairing repeats through the whole Mercedes fault list: B1026 and B1027 cover driver squib 2 on a dual stage airbag, B1028 and B1029 cover the front passenger squib, and B102C and B102D cover the driver emergency tensioning retractor. Knowing which half of the pair is stored tells you whether to hunt for a poor connection or for something bridging the wires.
High resistance on a driver circuit is nearly always mechanical. Something in the path is barely touching. The path itself is short, and the one part in it that moves every time the wheel turns is the contact reel, which most shops call the clock spring.
Circuit. N2/7 is reporting a live measurement it took at key on rather than a record of anything that happened to the car. Mercedes stores deployment events separately, and on the older numbering those read as codes in the 9000 block.
If B1025 turns up on a car with collision history, treat the resistance fault and the stored crash record as two jobs on the same repair order. Repair the circuit, then deal with the module's memory.
No. Resetting the module restores its memory and clears stored crash data, and a high resistance loop is a live fault the control unit measures again on the next key cycle. It will store B1025 right back.
Fix what the circuit is doing first. If the contact reel turns out to be the failed part, genuine OEM clock springs and driver airbags are listed by vehicle in the parts store. When the airbag deployed and N2/7 locked with crash data, our airbag module reset clears that record once the replacement parts are installed.
B1025 in this form is Mercedes-Benz, and the wording comes from the factory diagnosis list for the N2/7 restraint systems control unit. It appears across the C, E, S, CLK, SLK, and ML families and on the Sprinter, on any model whose restraint controller uses this fault set. Other manufacturers assign B1025 to their own circuits, and a generic code reader will happily print a definition from the wrong brand, so confirm the code came from a Mercedes control unit before you follow anything on this page.
Turn the ignition off, disconnect the battery, and give the system its discharge time before the wheel comes apart. Then work from the easy end. Unplug and reseat the airbag connector, check the pins for spread or corrosion, and inspect the contact reel ribbon for wear at the spool. Ask about recent work while you are at it, because this fault often follows a job that disturbed the column or the steering angle sensor.
If the loop measures correctly at the airbag and the code stays, the harness between the contact reel and N2/7 is the next section to check. Related codes are B1024 for the same circuit reading low and B1026 and B1027 for the second stage on the same airbag. If you need a Mercedes part we do not have listed, send a part request with the model and chassis number.
Related codes: B1024, B1026, B1027
Keep reading:
Code scope: Mercedes-Benz. 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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Mercedes-Benz parts and codes · Do not see it listed? Request a part or call 501-988-0611.