Comprehensive diagnostic guide for OBD-II code U0267

Note: U0267 is a vehicle-network (U) diagnostic trouble code. U-codes indicate data communication issues on the vehicle's network bus and are OEM-dependent in exact definition. The following guide synthesizes general OBD-II/network code troubleshooting concepts from established references and combines them with practical field approach. OEM-specific meaning of U0267 should be looked up in the vehicle's service information (OEM scanner/tech data) for exact diagnosis and affected modules.

Key facts from verified sources

• OBD-II diagnostic trouble codes are used by modern vehicles to indicate issues detected by onboard monitoring systems, including network-related faults (OBD-II provides P, B, C, and U categories).
• Powertrain codes are one subset of DTCs used to identify engine, transmission, and related driveline concerns; U-codes reside in the broader DTC framework that includes network/communication issues.
• Emissions-related testing and verification are part of OBD-II systems, but the core diagnostic approach for a U-code is to identify data bus issues, module communication loss, or gateway/ECU problems that affect multiple modules.

Symptoms

• The MIL (check engine light) is illuminated, often with other modules reporting faults or not displaying data (e.g., ABS, TCM, or body-control modules showing no data or errors).
• Multiple controllers intermittently fail to communicate; scan shows U0267 plus other U-coded or communication-related DTCs.
• Vehicle experiences intermittent starts or erratic operation when the data bus is unstable; some modules report data but others do not.
• After battery disconnect or wiring/repair, DTCs appear or reappear, sometimes after a short drive or a specific ignition state.
• After aftermarket electronics installation (alarms, infotainment, wiring harness changes), wireless modules or gateways begin to show communication faults.

What U0267 typically implies (OEM-specific meaning can vary)

• General interpretation: a data bus/network communication fault. It often indicates that one or more ECUs are not receiving or sending expected messages on the vehicle's communication network. Since exact meaning is OEM-specific, you must verify the OEM definition via service information before replacing hardware.

Probable Causes

• CAN bus physical layer issues (wiring, connectors, grounds) - ~35%
• Power/ground problems or wake-up/ignition-sense issues affecting multiple ECUs - ~20%
• Faulty or incompatible module firmware/software or a faulty gateway/router module - ~15%
• Aftermarket devices or improper wiring causing bus contention or interference - ~15%
• Battery/charging system issues or ignition switch problems causing intermittent bus activity - ~10%
• Faulty terminal blocks, chassis grounds, or wiring harness damage leading to intermittent communication - ~5%

Note on data sources: NHTSA complaint frequency data is not provided in the given sources. The percentages above are and typical patterns seen with network DTCs, not vendor-published probabilities.

Diagnostic Approach

1) Safety and preparation

• Ensure the vehicle is in a safe state to diagnose: vehicle on a level surface, parking brake set, ignition off before disconnecting any modules or wiring.
• Use a reliable, OEM-compatible scan tool or diagnostic interface to read the DTCs, freeze-frame data, and live data streams.

2) Confirm the DTC and gather OEM context

• Confirm U0267 is present and note any companion DTCs (especially other U-codes or P/B/C codes) that appear concurrently.
• Check for OEM-specific definitions: look up U0267 in the vehicle's service information (factory scan tool definitions or OEM tech data) to identify the exact meaning, affected modules, and recommended tests. OEM definitions vary and are essential for precise repair steps.
• Record freeze-frame data, current vehicle state (ignition ON vs. OFF), and any active monitor status.

3) Inspect power, grounding, and wake-up signals

• Inspect battery health and charging voltage. A marginal or fluctuating supply can cause modules to wake or wake in and out of sleep, triggering communication faults.
• Verify main power and ground points for the vehicle's network master controller/gateway and major ECU grounds. Poor grounding or corroded terminals can cause intermittent bus faults.
• Inspect ignition/switched power sources to ECUs. Some modules should wake with key on; if wake signals are missing or erratic, bus activity can degrade.

4) Visual inspection of the network and wiring

• Inspect CAN/vehicle network wiring harnesses for damage, pin mis-mating, chafing, water intrusion, or aftermarket harnesses that could introduce noise or shorts.
• Check harness connectors for corrosion, bent pins, or loose/incorrectly seated connectors. Ensure grounds are clean and properly torqued.
• Look for after-market devices that connect to the data bus (audio, telematics, alarm systems, remote starts). Disconnect these devices temporarily to see if bus communication stabilizes.

5) Data bus and module-level checks

• Using a diagnostic tool, review which modules are communicating. Note any modules that show no data, abnormal IDs, or timeouts.
• If possible, measure CAN bus activity with a scope or a tool that can display CAN High (CAN_H) and CAN Low (CAN_L) waveforms. Look for excessive voltage levels, dominant bus errors, or arbitration issues.
• Check CAN bus termination resistors (typical 60 ohms total for a properly terminated CAN network; improper termination can cause reflections and communication issues). Verify there is only one proper termination at each end of the bus.
• Verify that no single module is holding the bus in a constant dominant state (dominated lines) or causing mass data contention (a stubborn module that never releases the bus).

6) Power, wake-up, and gateway/module health

• Confirm that the gateway or central network controller (if present) is powered and logging messages. A faulty gateway can cause multiple ECUs to appear disconnected.
• Verify each critical CPU/ECU has proper power and ground and that no ECU is rebooting or resetting repeatedly (watch for repeated fault codes or intermittently cleared codes after power cycles).

7) Correlate with OEM-Defined Test procedures

• Because U0267's exact definition is OEM-specific, follow OEM diagnostic procedures for that code if available. This may include specific data stream checks, module reprogramming, or targeted replacements.
• If OEM guidance suggests a gateway/module replacement, verify wiring and confirm compatible software/firmware levels before replacement to avoid new conflicts.

8) Troubleshooting flow based on symptoms

• If several modules show communication failures but the battery and main power circuits are solid: focus on CAN bus physical layer (wiring, connectors, grounding) and gateway/module health.
• If comms appear to fail only after certain conditions (e.g., after a reset, during certain engine states, or after aftermarket installation): investigate wake-up signals, ignition-switched power to ECUs, and any aftermarket wiring that could be influencing bus behavior.
• If no additional DTCs are present aside from U0267: emphasize the network path, gateway, and core bus hardware rather than a single ECU.

9) Repair actions (prioritized)

• Repair or replace damaged wiring, connectors, and ground paths; restore proper ground integrity and remove any sources of noise on the bus.
• Disconnect aftermarket devices that tap into the data bus; re-test to see if bus communication stabilizes.
• Repair power/ground issues; ensure proper battery health and stable ignition power to ECUs.
• If OEM-defined, replace or reprogram affected modules per OEM instructions. Do not replace multiple modules unnecessarily-confirm the OEM-recommended fix first.
• Where a gateway or central module is confirmed as faulty, replacement should be performed with OEM-specified software/firmware and a re-learn/reconfiguration step if required.

10) Verification and validation

• After repairs, clear the codes and monitor the vehicle through multiple drive cycles to confirm that U0267 does not reappear and that all modules communicate normally.
• Verify that no new codes appear and that all monitors complete successfully.

Documentation and data collection to improve accuracy

• Save DTCs, freeze-frame data, and live data snapshots before and after repairs.
• Note which modules were communicating, any observable data bus errors, and the exact OEM definition of U0267 from service information.
• Record the actions taken (wiring repairs, connector reseating, aftermarket device removal, module updates) and the resulting vehicle behavior.

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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