Mercedes names every part in its restraint system with a component designation rather than a description, so a code reads as R12/13 or S68/3 instead of driver airbag or buckle switch. Learn the designations and the list turns into a wiring diagram you can follow.
Mercedes calls the airbag computer the restraint systems control unit. The factory diagnostic text addresses it by component designation rather than name, N2/7 in the Daimler tables for the C-Class era and N2/10 on other chassis. It mounts under the center console on the floor tunnel between the front seats.
That designation split is the first thing to check on any Mercedes code lookup, because two sites can give two meanings for one number while both quote real tables for different chassis. Model coverage is on our Mercedes-Benz airbag service page.
Mercedes numbers its restraint faults as B-codes, and the structure catches people out: the same physical part appears in three separate blocks depending on the kind of problem it has.
The squib designations are worth learning. R12/13 and R12/14 are driver airbag stages 1 and 2, R12/4 and R12/5 the passenger stages, R12/1 and R12/2 the front emergency tensioning retractors, R12/6 and R12/7 the rear ETRs, R12/20 and R12/21 the front side airbags, R12/22 and R12/23 the rear window airbags, and R12/25 the driver kneebag.
Mercedes does not publish a code reading crash recorded the way some manufacturers do. After a deployment the fired squibs read out of range, the control unit locks, and it reports itself defective through that large B1082 and B2Dxx block. That locked state is what a module-level crash data reset addresses, and it is why a Mercedes can come back from a body shop with everything replaced and the light still on.
Codes with a link have their own page. Crash data clears with a module reset; hardware and circuit faults need the part fixed or replaced first.
| Code | Meaning | Type |
|---|---|---|
| B1001 | Restraint systems control unit N2/7 is defective. | Hardware fault |
| B1002 | Restraint systems control unit, circuit 15R: no voltage when voltage is present at circuit 15. | Circuit fault |
| B1003 | Restraint systems control unit terminal 15R and 15 undervoltage. | Circuit fault |
| B1004 | Ignition circuit fault at R12/13, driver airbag ignition squib 1. | Circuit fault |
| B1008 | Ignition circuit fault at R12/4, front passenger airbag ignition squib 1. | Circuit fault |
| B100C | Ignition circuit fault at R12/1, driver emergency tensioning retractor squib. | Circuit fault |
| B100E | Ignition circuit fault at R12/2, front passenger emergency tensioning retractor squib. | Circuit fault |
| B1014 | Ignition circuit fault at R12/20, left front side airbag ignition squib. | Circuit fault |
| B1018 | Ignition circuit fault at R12/11, left rear side airbag ignition squib. | Circuit fault |
| B1022 | Restraint systems control unit coding is faulty. | Hardware fault |
| B1024 | Driver airbag ignition squib 1 circuit resistance too low. | Circuit fault |
| B1025 | Driver airbag ignition squib 1 circuit resistance too high. | Circuit fault |
| B1028 | Front passenger airbag ignition squib 1 circuit resistance too low. | Circuit fault |
| B102C | Driver emergency tensioning retractor squib circuit resistance too low. | Circuit fault |
| B1034 | Left front side airbag ignition squib circuit resistance too low. | Circuit fault |
| B1035 | Left front side airbag ignition squib circuit resistance too high. | Circuit fault |
| B1044 | Coding for the driver airbag ignition squib 1 circuit is faulty. | Hardware fault |
| B1052 | Coding for R12/25, the driver kneebag ignition squib, is faulty. | Hardware fault |
| B1054 | Component or signal wire to S68/3, driver-side seat belt buckle restraint systems switch. | Circuit fault |
| B1057 | Component or signal wire to S68/4, passenger-side seat belt buckle restraint systems switch. | Circuit fault |
| B105E | Incorrect sensor type fitted at A53/1, left side airbag and window airbag sensor. | Hardware fault |
| B1061 | Communication fault or cable fault at A53/1, driver-side side airbag and window airbag sensor. | Circuit fault |
| B1062 | A53/1, driver-side side airbag and window airbag sensor, is defective. | Hardware fault |
| B1064 | A54/1, right side airbag and window airbag sensor, is defective. | Hardware fault |
| B106C | Communication or cable fault at B48, front passenger seat occupied and child seat recognition. | Circuit fault |
| B106F | B48, front passenger seat occupied and child seat recognition, is defective. | Hardware fault |
| B1071 | External fault in the child seat recognition. | Hardware fault |
| B1075 | CAN communication is faulty. | Circuit fault |
| B1082 | Restraint systems control unit is defective. The first of a very large block reporting the same thing. | Hardware fault |
| B2D00 | Restraint systems control unit is defective, from the second internal-fault block. | Hardware fault |
| 9001 | Crash data stored. | crash |
| 9033 | Driver pretensioner circuit. | Circuit fault |
| 9069 | Passenger airbag circuit. | Circuit fault |
| 9116 | Seat occupancy sensor. | Circuit fault |
A generic OBD2 reader will not reach the restraint systems control unit. Mercedes codes come out of the factory software, DAS on older cars and XENTRY on newer ones, or an aftermarket tool with real Mercedes SRS coverage. A parts-store scanner reporting no codes while the light is on has not talked to that module.
Coding is a first-class concern here. A large share of the table is nothing but coding faults, several of them saying only that the control unit coding is faulty. Each squib has its own coding fault, so a car fitted with a kneebag it was not coded for sets B1052 alone. B1079 flags that the restraint unit coding and the EIS control unit coding are implausible against each other, which is what a mismatched module swap looks like.
The seat is where most Mercedes airbag lights start. Component B48, front passenger seat occupied and child seat recognition, is transponder-based and gets its own run of codes: only one transponder detected, communication faults, cable faults, the component defective, and an external fault in the child seat recognition. Aftermarket child seats, worn mat wiring and connectors kicked loose under the seat all land there.
The other steady one is voltage. B1002 is the unit reporting no voltage on circuit 15R when voltage is present at circuit 15, and B1003 is undervoltage at terminal 15R and 15. A tired battery or a corroded ground sets those before anything is wrong with a restraint component, so charging gets checked before parts get ordered.
They are quoting tables for different chassis. Mercedes addresses the airbag computer by component designation, N2/7 in the Daimler tables for the C-Class era and N2/10 on other chassis, and the numbering behind them is not identical. A lookup that does not match your model can be confidently wrong.
There is not one, at least not the way Ford or Hyundai publish it. After a deployment the fired squibs read out of range and the control unit locks and reports itself defective through the B1082 and B2Dxx blocks. That is why a car can come back from the body shop with every part replaced and the light still on.
Emergency tensioning retractor, Mercedes vocabulary for a seat belt pretensioner. R12/1 is the driver unit, R12/2 the front passenger, R12/6 and R12/7 the rear pair. A code naming one of those is about a belt, not an airbag.
Very likely. B1002 is the control unit reporting no voltage on circuit 15R when voltage is present at circuit 15, and B1003 is undervoltage at terminal 15R and 15. A weak battery or corroded ground sets those before any restraint component is faulty.
Keep reading:
Crash data clears with a reset of your own module. A hardware fault needs the part. Either way, call and we will confirm.
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