U2630

Code

Generic U — Network/User

Communication Bus Fault — Module Not Responding

Brand: Generic

Type: U — Network/User

Views: UK: 13 EN: 12 RU: 16

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Module has lost power or ground
Open or short in network wiring (CAN/LIN/FlexRay/MOST) to the module
Corroded or loose connector pins at the module or backbone splice
Missing or failed bus termination resistor(s)
Module internal failure (transceiver or MCU)
Blown fuse or disabled supply/ignition feed

Symptoms

MIL (check engine) or other warning lights illuminated
Functions controlled by the non‑responding module are inoperative or degraded
Intermittent or permanent loss of related vehicle features (e.g., ABS, transmission, body functions)
Multiple communication errors or related U‑codes logged
Intermittent starts, limp mode, or unexpected behavior after sleep/wake cycles

What to check

Confirm U2630 is current and note any accompanying codes and freeze frame data
Check battery voltage (12.6V nominal at rest) and charging system health
Inspect fuses and relays for module power/ignition feeds
Visual inspection of module connector, harness, and nearby splice points for damage or corrosion
Use a scan tool to poll the module and observe if it ever responds or shows intermittent communication
Measure CAN/LIN bus idle voltages at the module connector (CAN_H and CAN_L differential ≈ 2.5 V each, CAN_H ≈ 2.5–3.5V, CAN_L ≈ 1.5–2.5V depending on vehicle)

Signal parameters

Bus type: CAN (ISO 11898), LIN, FlexRay, MOST — confirm vehicle network type
CAN bit rate options: common values 125 kbps, 250 kbps, 500 kbps, 1 Mbps — verify expected rate
Idle voltage: CAN_H ≈ 2.5–3.5 V, CAN_L ≈ 1.5–2.5 V; differential ≈ 0 V recessive, ≈ 2 V dominant
Termination resistance: approx. 60 ohms across CAN_H and CAN_L (two 120 ohm terminators)
Message IDs and expected frequency for the module (consult manufacturer data for ID and transmission rate)
Bus states to observe: dominant/recessive transitions, bus-off, error frames, and excessive retries

Diagnostic algorithm

Record code and any related DTCs. Note occurrence: key on engine off (KOEO), running, or after sleep/wake.
Verify vehicle battery/charging system and relevant fuses/relays supplying the module. Repair low voltage or blown fuses first.
With ignition ON, use a scan tool to attempt to communicate with the affected module. Note if module appears briefly or never.
Visually inspect the module connector and harness for corrosion, looseness, damaged insulation, or rodent damage. Repair as needed.
Measure module power and ground pins at the connector with harness connected. Confirm proper voltage and continuity to chassis ground.
Measure CAN_H and CAN_L (or LIN) voltages at the module connector with ignition ON. Compare to expected values and check for shorts to 12V or ground.
Measure termination resistance across CAN_H and CAN_L with ignition off. Expect ~60 ohms; if open or very low, trace and repair termination network.
Use an oscilloscope or CAN sniffer to capture bus traffic. Look for the module’s message IDs, error frames, bus-off events, or abnormal waveforms.
If noise or short is present, isolate sections of the bus by disconnecting nodes/modules systematically to find the faulty device or harness section.
If power/ground and wiring check good and bus is healthy but module does not respond, suspect internal module failure — confirm by substitution with a known good module if available.
If module replacement or repair is performed, clear codes, perform relearn/programming if required, and verify operation through a full system scan and road test.
Document repairs and monitor for recurrence. If intermittent, consider harness repair or replacement of suspect connectors and re‑test.

Likely causes

Module supply or ground circuit fault (power/ignition fuse, relay, connector)
CAN bus wiring open/short at or near the module connector
Failed CAN transceiver inside the module
Missing or damaged termination resistor(s) causing bus reflections or bus‑off
Connector corrosion or bent pins interrupting communication

Fault status

⚠️ Status

Communication Bus Fault — a control module did not respond to network requests or message traffic is missing/erratic on the vehicle communications bus.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-4 hours