U1700

Code

Generic U — Network/User

Control Module Communication - Bus Off

Brand: Generic

Type: U — Network/User

Views: UK: 27 EN: 152 RU: 39

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Page language: EN

Loss of communication with the affected module(s)
Multiple U-codes or 'lost communication' faults present
Malfunctions or loss of systems controlled by the module (e.g., ABS, instrument cluster, HVAC)
MIL or warning messages illuminated
No or erratic network data visible on a scan tool
Modules entering limp/fail-safe modes

Read all stored and pending DTCs and freeze frame data with a scan tool
Identify which module reports BUS-OFF and note network name (CAN1/CAN2/CAN-FD)
Check battery voltage and main ground connections (stable 12V while cranking)
Inspect CAN connectors and harnesses for damage, corrosion, or recent repairs
Measure termination resistance across CAN_H and CAN_L (≈60 Ω with two 120 Ω terminators)
Measure idle voltages on CAN_H and CAN_L with key on (recessive ≈2.5 V each, differential ≈0 V)

Connect a capable scan tool; record all U-codes and which module reports BUS-OFF. Note network name.
Confirm battery voltage stable ≥12 V and good main grounds before continuing diagnostics.
Visual inspection of wiring harnesses, connectors, and modules on the affected network for damage or corrosion.
Check termination resistance across CAN_H and CAN_L with ignition off (~60 Ω expected).
Measure CAN_H and CAN_L voltages with key on (recessive ~2.5 V each).
Use an oscilloscope or CAN bus analyzer to view traffic and error frames. Look for continuous dominant state, repeated error frames, or lack of traffic.
Isolate sections: disconnect non-critical modules or aftermarket devices one at a time (with proper procedures) to see if bus recovers from BUS-OFF.
If a specific module transceiver is suspected, test/replace transceiver or swap with known-good identical module if available.
Repair wiring, connectors, or termination as required. Clear codes and attempt to reinitialize the bus (some modules recover only after key cycles or programmed reflash).
After repair, clear codes, verify normal bus traffic with scan tool/scope, and confirm all affected systems operate correctly. Road test if needed.