Comprehensive diagnostic guide for OBD-II code U0142

• U0142 is a U-code in the OBD-II generic code set, which covers network/communication issues between modules on the vehicle's CAN bus. The exact module involved can vary by vehicle (e.g., steering, gateway, ABS, BCM), so you must correlate with the vehicle's topology and service data. This interpretation aligns with the OBD-II framework described in general terms by the Diagnostic Trouble Codes and Powertrain Codes sections of the Wikipedia OBD-II article. See: Wikipedia - OBD-II: Diagnostic Trouble Codes; Wikipedia - OBD-II: Powertrain Codes.
• For standard code definitions, consult GitHub definitions or repositories that catalog DTCs (U0142 definitions are vehicle-specific and may map to "Lost Communication with [Module]" on the CAN network).
• Since this guide relies on general OBD-II network code concepts, it does not assume a single module: treat U0142 as a network fault that may involve any module on the CAN bus depending on the vehicle.

1) What U0142 means (definition and scope)

• U0142 is a network-related diagnostic trouble code (DTC) that indicates a loss of communication on the vehicle's CAN network with a specific module or gateway. The exact target module is vehicle-specific (for example, steering-related modules, gateway module, ABS/ESC module, body-control/module gateway, etc.).
• Because it's a communication fault, other codes (P, B, C, or U) may appear concurrently, reflecting which modules could not talk to the requesting controller. In some vehicles, U0142 may be accompanied by wake/heartbeat messages missing, incorrect node IDs, or sporadic CAN error frames.

2) Common symptoms you may see reported by users

• MIL (Check Engine Light) or service light illuminated, sometimes along with other U-code or P-code indicators.
• Steering-related warnings or limited steering assist capability in vehicles with steering-angle sensors (SAS) or steering assist modules involved in the network.
• Instrument cluster abnormalities, intermittent or stuck gauges, or non-responsive digital displays due to CAN data loss.
• ABS/traction control indicators or erratic ABS-related messaging if the ABS controller is on the CAN bus and loses communication.
• Cruise control, power windows, door locks, or other body/electrical features behaving intermittently or not responding.
• In some cases, customers report intermittent driveability concerns (loss of information on the dash, warning lights turning on/off) without obvious mechanical drivability faults.

3) Likely causes (probability distribution, vehicle- and symptom-dependent)

Because the literature sources don't provide vehicle-wide NHTSA-based statistics specifically for U0142, use ASE field experience to gauge likelihood. Typical patterns tend to cluster around the CAN network and gateway modules:

• CAN bus wiring/connectors and grounding issues (most common): damaged insulation, pin corrosion, loose connections, water intrusion, bent pins, or misrouted wiring can disrupt message timing and bus arbitration, producing U0142.
• Faulty CAN gateway or central module(s): gateway modules that route messages between CAN buses (e.g., body/electrical gateway) can fail or have software issues, causing widespread communication dropouts.
• Faulty module(s) on the CAN network (including Steering, SAS, ABS, BCM, or steering-related control modules): a failed module may stop transmitting or actively disrupt the bus, causing the network to report lost communications with the module(s) that rely on it.
• Power and ground issues affecting multiple modules on the CAN network: low battery voltage, bad grounding, or a failed alternator can cause modules to reset or fail to wake up, creating transient or persistent U0142s.
• Software/firmware issues: mismatched or corrupted software in one or more modules can lead to improper CAN wake-up, incorrect message timing, or failure to respond.
• Environmental factors: moisture, corrosion, or damaged harnesses in engine bay or under-car areas can lead to intermittent CAN faults.
  Note: The exact distribution will vary by vehicle; in many cases, wiring, connectors, and the gateway/module health dominate. If a vehicle has known CAN topology or a documented gateway that's prone to failure, give that area priority.

4) Data you should collect and tools you'll need

• Vehicle details: make, model, year, VIN, and any known prior electrical/network work.
• Scan tool data: perform a full CAN-capable OBD-II scan; record DTCs (U0142 and any related codes such as U0100, U0101, U0121, U0130, etc.), freeze-frame data, and any live data related to CAN bus activity (message IDs if your tool supports it).
• Power/ground verification: measure battery voltage with engine both off and at idle; ensure stable 12.6-14.8 V range when running; check engine ground strap continuity to the chassis and to the engine block.
• Visual inspection: scan for obvious wiring damage, loose connectors, corrosion, chafed harnesses, or water intrusion in fuse/relay boxes, under-hood connectors, and near steering/ABS modules.
• CAN topology reference: vehicle service data or OEM diagrams showing which modules are on which CAN buses and how gateway routing is configured.
• If available: use a CAN bus analyzer or oscilloscope to observe bus activity, look for abnormal bus errors, arbitration lost frames, or idle/busy times, and confirm that messages are being transmitted and received by the modules involved.

5) Diagnostic procedure (step-by-step)

Step 1: Confirm scope and related codes

• Confirm U0142 is current and not historical. Note any related codes (U0100, U0101, U0121, U0131, etc.) that indicate missing wake-ups, lost communication, or bus faults.
• Check for vehicle-specific notes in service data about the gateway or steering/network modules.

Step 2: Basic power/ground health

• Verify battery condition and charging system: ensure battery voltage is stable 12.6-12.8 V with engine off, and 13.8-14.8 V with engine running.
• Check main fuses/relays supplying power to CAN control modules and the gateway.
• Check chassis and engine grounds for corrosion, looseness, or high resistance. A high resistance ground can mimic network faults.
• If a known-good battery or alternator test helps reproduce or eliminate U0142, use that to confirm power integrity.

Step 3: Inspect CAN wiring and connectors

• Visually inspect main CAN high (CANH) and CAN low (CANL) trunks and critical branch wires for damage, kinks, abrasion, or water exposure.
• Inspect connectors at major modules on the CAN network: gateway, SAS/steering module, ABS/ESP module, BCM, and any other involved controllers. Look for bent pins, corrosion, or improper mating.
• Check for improper aftermarket wiring (alarm systems, remote start, radio amps) that could inject noise or connect to CAN lines.

Step 4: Identify and test likely modules

• Based on the vehicle's CAN topology, identify modules most likely to be involved (gateway, steering/SAS, ABS/ESP, BCM, etc.).
• Check for module-specific fault codes (not just U-codes). Some vehicles will store module faults when a module fails to respond. Note any module that shows faults or non-wake events.
• If a module supports wake-up or sleep commands, verify that wake signals are being sent and received as expected.

Step 5: Isolate with controlled tests

• If feasible, perform a stepwise isolation:
  • Disconnect suspected module(s) one at a time and clear U0142. If U0142 clears but a different code appears (or a specific module stops communicating), you've likely isolated the problematic module or a bus interaction.
  • Alternatively, alternate the suspected gateway/module by swapping with a known-good unit (when allowed by manufacturer confirms compatibility and programming).
• While isolated, monitor CAN traffic with a bus analyzer to see if other modules regain communication and if the network stabilizes.

Step 6: Check for software/firmware issues

• If the vehicle has current service bulletins or recalls for gateway, SAS, or steering control modules, review and apply software/firmware updates per OEM guidelines.
• Confirm there are no mismatched software levels among CAN modules; mis-match can cause one module to fail to communicate correctly.

Step 7: Look for environmental causes

• If the issue occurs after a rain or car wash, re-check for moisture intrusion in connectors and harnesses, particularly around steering and gateway modules.
• Inspect sealing and grommets around steering column, dash areas, and engine bay harness routes.

Step 8: Re-test and validate

• After repairs or component swaps, clear DTCs and perform a road test across a few miles in varying speeds and loads to re-check for recurrence.
• Monitor CAN network behavior during the test (if a CAN analyzer is available) to ensure messages are being transmitted/received consistently and there are no new errors.

6) Possible repairs and fixes (typical actions)

• Repair or replace damaged wiring harnesses and connectors on CAN lines; reseat connectors with proper contact integrity; apply dielectric grease where appropriate and re-torque to spec.
• Replace faulty module(s) identified as communication offenders (for example, gateway module, SAS steering module, ABS/ESP module, or BCM). After replacement, ensure proper programming, coding, or initializations per OEM procedures.
• Correct power/ground issues: repair ground straps, ensure solid battery ground, fix corroded or loose battery connections, and address any parasitic drains that may destabilize CAN nodes.
• Update or reflash module firmware/software as recommended by the OEM; ensure compatibility across all related modules.
• Remove aftermarket devices or non-factory wiring that may interfere with CAN signaling (alarm systems, audio amplifiers, etc.), or re-route as needed under OEM guidance.
• If required by OEM testing, perform steering angle sensor calibration or steering-related module initialization after component replacement or software update.

7) Special vehicle considerations

• Steering and SAS-related networks can be safety-critical. If steering modules are involved, ensure all steps comply with vehicle safety protocols and, if needed, calibration or alignment is performed after service.
• Some vehicles require service procedure sequences (e.g., module re-learn, steering rack calibration, or drive-cycle requirements) post-repair to reestablish proper CAN communication.

8) Verification and validation guidance

• Clear all codes, then perform a representative drive cycle (city and highway) while monitoring for reoccurrence of U0142 and any related codes.
• If a CAN bus analyzer is available, verify that:
  • All expected modules are awake and communicating.
  • No persistent error frames are present on CANH/CANL.
  • Messages from the suspected module are received by the gateway and other modules in the network.
• Confirm that any replaced modules initialize correctly and that no new fault codes appear.

9) Safety and risk considerations

• CAN network faults that involve steering or braking modules pose critical safety risks. Work in a controlled environment and follow OEM service procedures for disassembly, module replacement, and calibration.
• Ensure vehicle is secure, engine is off when performing harness work, and any required safety gear is used during diagnostics and testing.

10) Documentation and troubleshooting notes

• Document exact modules involved, wiring repairs, calibration steps performed, software/firmware versions updated, and test outcomes (with timestamps).
• Note any vehicle-specific caveats (e.g., "gateway must be reprogrammed after steering module replacement" or "certain models require steering angle recalibration").
• If you encounter inconsistent symptoms or intermittent U0142 presentations, consider environmental and battery-related causes as part of root-cause analysis.

11) Quick reference checklist

• Confirm U0142 and related codes; gather freeze-frame data.
• Verify power/ground health and battery/charging stability.
• Visually inspect CAN wiring, connectors, and grounds.
• Identify and diagnose likely modules on CAN network; review module fault codes.
• Use CAN bus monitoring to assess message flow and identify missing/errant frames.
• Isolate modules and test network with controlled disconnections.
• Apply software/firmware updates per OEM; calibrate as required.
• Repair wiring/connectors or replace faulty modules as indicated.
• Re-test drive and re-scan to confirm repair success; monitor for recurrence.

12) How to cite and corroborate

• For general code structure and the existence of OBD-II trouble codes, see Wikipedia: OBD-II - Diagnostic Trouble Codes; Wikipedia: OBD-II - Powertrain Codes.
• For standard definitions and module mappings (e.g., U-code semantics and typical category of network faults), consult GitHub repositories that catalog DTC definitions (U0142 and related codes). Use vehicle-specific OEM service data to verify exact module mapping and re-learn/calibration requirements.
• If available, reference NHTSA complaint trends for U0142 to understand real-world frequency patterns; in this guide, no explicit NHTSA data is provided for U0142, so probabilities are and common network fault patterns.

Closing note

• U0142 indicates a network communication problem on the vehicle's CAN bus. The root cause is commonly a wiring/connector issue or a faulty gateway/module, though steering, ABS, and BCM modules can also be involved depending on vehicle topology. A systematic approach-verifying power, inspecting wiring, testing modules, and validating with CAN bus analysis-will usually identify the fault source. Always prioritize safety when diagnosing and repairing steering- or braking-related network faults, and follow OEM service data for calibration and re-learn procedures after repairs.

Cited references

• GitHub definitions: Standard OBD-II code information (used to corroborate the definition and mapping of U0142; exact module mapping is vehicle-dependent).
• (Note on how to use sources): If conflicts arise between sources, mention both perspectives; if NHTSA data is unavailable for U0142, rely on ASE field experience for probability estimates.

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.

---