U2125 — CAN-BUS no communication with global position system/telematic system, GPS/TMS

U2125 is stored when the ECU sees no signal on CAN bus communication. That describes how the circuit is behaving, not which part has failed — the wiring, the connector and the component itself can all produce it, which is why the checks below start with the cheapest.

Common causes

The cause is almost always one of a few things. Here they are — U2125 rarely comes from anything outside this list:

• Module has no power or no ground
• Broken bus wire or a bad splice in the network
• The module itself has failed
• Terminating resistor or bus fault taking the network down

Where to start

In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:

1. Check power and ground at the module before suspecting the module itself
2. Read whether other modules on the same bus also report faults — that separates a network fault from a single module
3. Inspect connectors at the module and any inline joints
4. Measure bus resistance across the two lines at the diagnostic socket
5. Replace the module last, once supply and network are proven good

That is what holds for U2125 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.