Comprehensive diagnostic guide for OBD-II code U0105

Lost Communication With [Module] on the vehicle's data bus

Important Notes

• What U codes mean: In OBD-II, U-codes are network/communication trouble codes. They indicate a loss of communication between control modules on the vehicle's data bus. This makes them particularly sensitive to wiring, connectors, power/ground, and the CAN network health.
• Manufacturer-specific target: The exact module that U0105 refers to is defined by the vehicle's make/model and its diagnostic mapping. A common scenario is "Lost Communication With [ABS/BCM/TCM/etc.]" depending on the vehicle. GitHub definitions typically list U0105 as a Lost Communication With a specific control module, but the exact target varies by OEM.
• Practical note: Because U0105 is network-related, the root cause is often somewhere in the CAN (or other vehicle bus) network: wiring/connector faults, damaged modules, power/ground issues, or a problematic gateway/interface. This guide treats U0105 as a system-wide network symptom with vehicle-specific module targets.

Symptoms reported by real users (typical, not vehicle-specific)

• Dashboard/cluster warnings illuminate and may flash or stay on (ABS/ESP/airbag/BCM indicators depending on the target module and vehicle).
• Other systems on the same network behave inconsistently or stop responding (e.g., ABS, traction control, cruise control, instrument cluster, power mirrors/locks, HVAC control).
• A "lost communication" type message appears during a scan tool readout, sometimes with related U0xxx codes or P0xxx codes when the scan tool polls other modules.
• In some cases, the vehicle starts and runs, but specific subsystems fail or report missing data, and clearing the codes may reappear after a road test.

Diagnostic Approach

1) Confirm the code and context

• Record the exact U0105 definition from the vehicle's OEM diagnostic map (since U0105 is not universal across all makes). Note any accompanying DTCs (other U-codes, P-codes, or B/C codes). Freeze-frame data can help identify ignition state, engine run status, and network conditions at the time the code set.
• Wikimedia notes that DTCs (including U-codes) indicate monitored parameter abnormalities; when multiple network-related codes appear, the issue is often network/communication related rather than a single module fault. Use that context to guide your flow.

2) Vehicle and system scope

• Identify which module(s) could be on the bus in your vehicle (ABS, BCM, TCM, Instrument Cluster, Gateway/ECU, HVAC, Steering/AWD control, etc.). The exact target depends on the make/model.
• Check for other network symptoms: failure of multiple modules, deadCAN devices, or intermittent bus activity. If many modules report failures, it's more likely to be a bus/network issue rather than a single module failure.

3) Gather data with the right tools

• Use an advanced OBD-II scanner capable of CAN (and vehicle-specific protocols) and, if possible, a CAN bus analyzer or oscilloscope to view bus activity (CANH/CANL). Look for error frames, dominant/recessive patterns, and missing arbitration messages.
• Where available, retrieve live data from modules and note any timeouts or lack of responses from modules that should be on the network.

4) Initial non-invasive checks

• Visual inspection: Scan for obvious wiring harness damage, loose connectors, corrosion, moisture intrusion, or aftermarket wiring adapters that might interfere with the bus.
• Power and grounds: Check that the vehicle's main power feed to the network is present (12V), ignition-switched power to modules as required, and chassis ground integrity. A flaky power/ground path to one or more modules can cause intermittent network communication.
• Fuses and fusible links: Confirm all related fuses are intact and that any inline fusible links protecting the network aren't damaged.

5) Inspect the CAN/Network health

• Confirm termination: Most CAN networks require proper termination at the two ends of the bus (typically 120 ohms total, sometimes separate terminators). Missing, damaged, or extra terminators can cause communication faults.
• Inspect CAN wiring length and integrity: Check for pin damage, bent pins, pin oxidation, and traceability of the CAN lines across modules.
• Check for node conflicts or short-to-supply/ground: A module pulling CAN lines high or low abnormally can cause widespread communication failures.

6) Identify the target module and verify

• With OEM-specific tooling or OEM service manuals, identify which module is the primary target for U0105 on this vehicle.
• Attempt to poll the target module directly (service mode or diagnostic session). If the target module does not respond, keep investigating network health and power/ground before concluding the module is bad.

7) Module-specific checks (while keeping network root in mind)

• If the target is ABS/ESC:
  • Inspect wheel speed sensors, tone rings, and ABS wheel harnesses for damage or corrosion.
  • Check ABS module connectors for proper seating and pin condition.
  • Verify power to ABS module and its ground; look for abnormal sensor data that might overwhelm the network.
• If the target is BCM (body control module):
  • Inspect door modules, lighting circuits, and central locking harnesses for corrosion/damage; BCM is often a central node on the network.
• If the target is TCM (transmission):
  • Inspect transmission harnesses; ensure there's no corrosion near the TCM connector; check 12V and ground at the module.
• If the target is Instrument Cluster:
  • Check the cluster harness for bent pins, corrosion, or poor ground; ensure the cluster can communicate on the bus and that its connectors aren't damaged.
• If the target is Gateway/ECU:
  • Gateway faults can cause cascading U-codes. Inspect gateway connectors and the routing of the network; look for improper aftermarket devices or rewiring that could alter network topology.

8) After-repair verification

• Clear codes after repairs and perform a thorough road test.
• Confirm that U0105 does not reappear; check for any related DTCs.
• Validate normal operation of all subsystems previously affected by the network issue (ABS, cluster, HVAC, etc.).

Cause Probability

Note: do not contain explicit NHTSA complaint data for U0105. These percentages are informed by general field experience with network-related DTCs and typical failure patterns in the automotive industry. When available, use OEM data and NHTSA complaint patterns; otherwise, use professional diagnostic experience.

• CAN bus wiring/termination issues (wiring harness damage, loose connectors, corroded pins, failed terminators): 40-50%
• Faulty or failing target module on the network (ABS BCM TCM Instrument Cluster Gateway etc.): 20-30%
• Power/ground issues to the network or to individual modules (fused supply, ignition feed, chassis ground): 10-20%
• Protocol/communication interface problems or gateway issues (misconfigured baud rates, recent reprogramming, compatibility issues): 5-15%
• Aftermarket devices or external wiring affecting bus (alarms, radios, remote starts, adapter harnesses): 5-10%
• Note: If multiple modules show communication issues, prioritizing bus health and power/ground becomes even more critical, as the root cause is often a network fault rather than a single module fault.

What to document in service notes

• Vehicle year, make, model, engine, and Transmission.
• Exact DTCs (including any secondary codes) and freeze-frame data.
• Description of observed symptoms and when they occurred (e.g., during cold start, during driving, after ignition on, etc.).
• Wiring/component inspection results and any observed damage.
• Power/ground test results, including voltage readings and grounds check.
• CAN bus test results (wiring resistance, termination status, observed CANH/CANL activity).
• Module identification and any attempts to directly communicate with target module (response, lack thereof).
• Repairs performed (wiring repaired, connectors replaced, modules updated, software reflash, etc.).
• Verification steps and road test results.

Tools and references

• Tools: Advanced OBD-II scanner with CAN capabilities, CAN bus analyzer/oscilloscope, multimeter, power probe, wiring diagrams/service manuals for the vehicle, OEM diagnostic tools if available.
• Reference notes:
  • Wikipedia - OBD-II: Diagnostic Trouble Codes: U-codes are network/communication trouble codes; DTCs cover various subsystems. This supports the network-focused approach for U0105.
  • Wikipedia - OBD-II: Powertrain Codes: Context on how codes relate to powertrain and connected subsystems; supports the idea that U-codes cross multiple modules.
  • GitHub (definitions): Standard code information for U0105 is generally described as "Lost Communication With [Module]"; exact module varies by OEM. Use the vehicle's service information to identify the targeted module.

Safety Considerations

• Always follow the vehicle's service manual for electrical safety. When working on the network, ensure battery discharge is controlled; disconnect the battery if required when working on power/ground or when accessing airbag-related systems (as applicable per vehicle and model).
• If the vehicle has airbags or high-voltage systems, follow OEM safety protocols and disconnect procedures. Some maintenance steps may require special tools and software access.
• Avoid creating new faults by unplugging connectors or installing aftermarket devices without proper knowledge of the CAN topology.

Sample diagnostic path (condensed checklist)

• Confirm U0105 and any related codes; review freeze-frame data.
• Identify the most probable target module(s) from OEM service information.
• Inspect power and grounds to the network and to the suspected module; check related fuses.
• Inspect CAN bus wiring for damage, corrosion, or improper routing; verify termination.
• Check for aftermarket devices or recent wiring changes that could affect the network.
• Attempt to communicate with the suspected module; verify response and data.
• If needed, trial-replace the suspected connector or module only after confirming the fault source and ensuring compatibility.
• Clear codes and perform a road test; confirm no reoccurrence of U0105 and verify all related systems function normally.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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