U2113 — CAN-BUS no communication with sensing and diagnostic module, SDM, airbag

U2113 means: CAN-BUS no communication with sensing and diagnostic module, SDM, airbag. That is the standard definition — what actually triggered it on a given car depends on the engine.

General steps

These apply to most OBD codes and are the right starting point before replacing anything. They are not specific to this code — for that, ask me about your car below.

1. Read codes from ALL modules — the U code says which module is not answering; that module usually holds its own code for the cause.
2. Check power and ground to the named module (fuse, relay, connector) — lost supply is the usual cause, not the module itself.
3. Measure the CAN bus: about 60 Ω between CAN-H and CAN-L with ignition off and battery disconnected; ~120 Ω means a missing terminator.
4. Look for corrosion where water gets in: connectors under the seats, the boot lid area, the passenger footwell.
5. A weak or old battery sets U codes during cranking — check voltage while starting.
6. If the module was replaced recently — it needs coding/adaptation to the car with a brand scanner.

That is what holds for U2113 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.