U0051

Code

Generic U — Network/User

Vehicle Communication Bus C (-) Open

Brand: Generic

Type: U — Network/User

Views: UK: 24 EN: 27 RU: 26

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Page language: EN

Read all stored U- and manufacturer-specific codes and note freeze frame/data
Visual inspection of CAN bus C wiring, connectors, and ground points for damage or corrosion
Backprobe CAN_L at a module connector with key ON, engine OFF to measure voltage
Measure resistance between CAN_H and CAN_L with ignition OFF (should be approx. 60 Ω for two 120 Ω terminators in parallel)
Check continuity of CAN_L between modules and to network splice points (expect low ohms)
Use an oscilloscope to view CAN_H and CAN_L waveforms while the network is active; look for missing signals or stuck/flat line on CAN_L

CAN recessive voltage (both lines) ≈ 2.5 V (key ON, bus idle)
CAN dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Differential voltage when idle ≈ 0 V; when transmitting ≈ 2 V
Termination resistance measured across CAN_H and CAN_L ≈ 60 Ω (two 120 Ω terminators in parallel)
Open-circuit on CAN_L: DMM may show floating voltage, battery voltage, 0 V, or infinite resistance to other modules

Record all current/ pending U-codes and freeze-frame data. Attempt to communicate with modules on Bus C with a scan tool.
Perform a visual inspection of wiring, connectors, and known splice points for Bus C. Repair obvious damage.
With ignition ON (engine OFF) backprobe CAN_L and CAN_H at a known good module and note voltages. Compare to expected signal_params.
With ignition OFF, measure resistance across CAN_H and CAN_L at a convenient access point. Expect ~60 Ω. If open or very high, suspect missing/ open terminator or open conductor.
Check continuity of the CAN_L conductor between modules and splices. Locate open by dividing the bus: unplug modules or disconnect harness branches and re-measure until the open segment is isolated.
Use an oscilloscope on CAN_H and CAN_L while the network is active to confirm message activity and identify a stuck/floating CAN_L line. A flat or noisy line indicates open/failed transceiver.
Inspect and, if necessary, repair or replace corroded connectors, damaged wires, or open splices. If a single module causes the open when connected, suspect that module's transceiver and consider replacement or bench testing.
After repair, clear DTCs, verify normal CAN voltages and waveforms, confirm all modules communicate, and road test to ensure fault does not return.