U0157 - Lost communication with Information Center 'B'
System
Network & Communication (CAN-bus)
Technical Description
The control module has detected a fault in the Data Bus Communication (Information Center 'B') (U0157). Node involved: a node on the vehicle communication network. Carried over the vehicle data bus. The "B" designation identifies one specific module or bus branch among several identical ones — verify the correct connector against the wiring diagram. Communication with the module has dropped out entirely — the controller no longer receives any frames from it on the data bus.
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Check for "a node on the vehicle communication network" (U0157) (Action ()) | Mätning | Measure ignition supply and ground right at the module connector, then check CAN continuity from the module pins back to the gateway. | Vehicle data bus |
| CAN Termination (OBD pin 6 ↔ 14) | Resistance (Ω) | 60 Ω (two 120 Ω in parallel) | Battery disconnected, ignition OFF |
| CAN-H / CAN-L Bias Voltage | Voltage (V) | CAN-H ≈ 2.5 - 3.5 V, CAN-L ≈ 1.5 - 2.5 V (recessive ≈ 2.5 V both) | Ignition ON, bus active |
| Information Center 'B' – Power and Ground | Voltage (V) | Supply 11.8 - 14.4 V / ground drop < 0.1 V | At module connector under load |
Vehicle data bus
Battery disconnected, ignition OFF
Ignition ON, bus active
At module connector under load
Oscilloscope Waveform Analysis
10 µs/div, 1 V/divPossible Causes
The module has lost power or ground, or the bus stub feeding it is broken
Bus segment:look up topology, speed and termination in the wiring diagram.
Check the two termination resistors (120 Ω each) — a broken or removed terminator produces reflections and the same fault class.
A chafed, pinched or heat-damaged section of the twisted bus pair — the segment often passes a sharp edge or hot surface.
A single babbling node with a faulty bus transceiver can drag the whole segment into the same fault state.
Symptoms
Recommended Solution
Measure ignition supply and ground right at the module connector, then check CAN continuity from the module pins back to the gateway.
Measure bus resistance across CAN-H/CAN-L, ignition off: 60 Ω normal, ~120 Ω = a terminator/branch missing, <10 Ω = conductor-to-conductor short.
Scope CAN-H and CAN-L together, ignition on, and judge whether the fault is an open (one trace flat), a short (traces collapsed together) or impedance (ringing).
Halve the segment:disconnect half the bus at a central splice and re-measure — the fault is in the half where the reading does not return to normal.
Disconnect modules on the segment one at a time; if the bus recovers when one particular module is unplugged, that node transceiver is the disturbance.
Confirm from the wiring diagram which physical module/branch is designated "B" — mixing it up with the sister module is a common error.
Mechanic's Tip
If several modules drop together the fault is on the backbone or gateway; if only this one drops, the fault is local to the module.