U0048

Code

Generic U — Network/User

Vehicle Communication Bus C (+) Open

Brand: Generic

Type: U — Network/User

Views: UK: 21 EN: 28 RU: 19

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Page language: EN

Broken or damaged CAN Bus C (+) wire (open circuit)
Disconnected, corroded or loose connector on CAN Bus C (+)
Failed module or ECU with internal transceiver open on CAN Bus C (+)
Faulty splice, junction block, or wiring harness damage (chafing, rodent, collision)
Removed or blown fuse feeding an intermediate junction (if present)
Aftermarket equipment or repairs that interrupted the bus wiring

MIL (Check Engine) or multiple communication DTCs present
Loss of communication with one or more modules on Bus C (modules unresponsive to scan tool)
Related vehicle features inoperative (depending on which modules are on Bus C)
Intermittent communication faults that clear when connectors/wiring moved
No CAN waveform or abnormal voltages measured on Bus C (+) line

Scan all modules and record U-codes and module(s) not responding
Visually inspect wiring, connectors and splices along CAN Bus C routing for damage, corrosion or disconnection
Check for blown fuses or removed service connectors that affect the bus wiring
Measure DC voltage from Bus C (+) to vehicle ground with key ON
Measure resistance between CAN_H and CAN_L with key OFF — expected ~60 ohms (two 120 ohm terminators in parallel)
Backprobe and wiggle test connectors while monitoring voltages and communication

Expected idle (recessive) voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both)
Expected dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Resistance across CAN_H to CAN_L (key off): ≈ 60 ohms (two 120 ohm terminators in parallel)
With an open CAN_H (Bus C +): CAN_H may be stuck at an abnormal voltage (floated or pulled to supply/ground), low/no differential and no valid CAN frames on the bus
Oscilloscope: absent or distorted CAN frames, low amplitude, or only one-wire activity

Safely record all stored DTCs and freeze frame data. Verify U0048 is current and note any other communication codes.
Identify all modules, junctions and connectors on CAN Bus C using the vehicle wiring diagram.
Perform a visual inspection of the entire Bus C wiring harness, connectors and grounding points for obvious damage or disconnection.
With vehicle OFF, measure resistance between CAN_H and CAN_L at a convenient connector; expect ≈60 Ω. If open (infinite), suspect open circuit in one conductor.
With key ON (engine off), measure DC voltage CAN_H to ground and CAN_L to ground. Compare to expected idle voltages (~2.5 V). Abnormal CAN_H supports open/float condition.
Use an oscilloscope or CAN bus tester to look for valid frames and differential voltage. If CAN_H shows no activity while CAN_L does (or vice versa), isolate the open by disconnecting modules/junctions sequentially and retesting.
Backprobe and wiggle suspect connectors while monitoring to reproduce the fault. Repair or replace damaged connectors, wires, or terminal pins found open.
If a module’s transceiver is suspected, disconnect that module and recheck the bus; replacing the faulty module may be required if it causes the open.
After repair, clear codes, verify normal bus voltages/waveforms and confirm communication with previously unresponsive modules. Road test to confirm fault does not return.