B1008 is a fault in the ignition circuit for component R12/4, which is Mercedes wording for the front passenger airbag ignition squib 1. That is the first stage firing element of the passenger bag. The restraint systems control unit, component N2/7, checks the circuit with the key on and stores the code when the reading falls outside its window.
Mercedes numbers components instead of naming positions, and reading the numbers is half the diagnosis. N2/7 is the restraint systems control unit. R12/4 is passenger airbag squib 1 and R12/5 is passenger airbag squib 2. On the driver side, R12/13 and R12/14 are squib 1 and squib 2. The belt tensioners carry their own numbers in the same R12 family, which is how one fault list covers the whole system.
B1008 and B1009 are the pair the current code list assigns to the R12/4 circuit. The older Mercedes numbering split that same circuit into six entries: 9140 for a short circuit to ground, 9141 for a short circuit to positive, 9142 for resistance too low, 9143 for resistance too high, 9144 for faulty coding, and 9147 for the circuit shorted to another ignition circuit. Whichever list your scan tool uses, read the full fault text along with the number, because the text names the actual condition and the number alone does not.
A firing circuit on these cars reads in the low single digits of ohms, so a film of corrosion on a terminal is enough to push the measurement outside the limit.
Circuit. The control unit is reporting a measurement on a pair of wires, and that number changes only when the hardware changes. On a car with no accident history it is pointing at a connector or at the bag.
After a deployment the picture is different. The fired squib leaves the circuit open, the code sets, and the control unit is separately holding the crash record from that impact. Both have to be dealt with, and each is handled a different way.
Not the circuit fault. A control unit holding a locked crash record is what our reset is for, and it does nothing for a corroded terminal or a spent airbag.
Repair the hardware first. Once the correct passenger airbag is installed and the connectors are clean and latched, send the control unit in for an airbag module reset so your original unit goes back in the car. If the belts locked or the tensioners fired in the same impact, our seat belt repair covers those assemblies.
B1008 with this meaning belongs to the Mercedes-Benz restraint code list, where the fault text names N2/7 and R12/4 directly, and it appears across the passenger car model series that use that list. If your report shows a four digit number in the 9100 range instead of a B code, you are reading the older list and the component numbers still apply the same way. Other manufacturers assign B1008 to something else entirely, so match the code to a Mercedes scan report before working from this page.
Turn the key off, disconnect the battery, and give the system time to discharge before reaching behind the dash. Then get to the passenger airbag connector and inspect it rather than testing through it. Look for green film, for a terminal that has pushed back into the housing, and for a lock that never engaged.
Write down the full fault text from the scan tool along with the number, because a short to ground, a short to positive and a resistance reading out of range each send you to a different part of the circuit. If the bag turns out to be the failed part and you cannot find it listed, send the part number through our parts request form. Our Mercedes-Benz page covers the parts and services we handle for these vehicles.
Related codes: B1009, B100A, B100B
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.