Comprehensive diagnostic guide for OBD-II code U0137

Overview and definition

• What the code means: U0137 is a universal OBD-II network/communications trouble code. In the OBD-II framework, U-codes pertain to network or data link issues between vehicle control modules. The exact module target and network segment can vary by manufacturer, but the common theme is loss or degradation of digital communication on the vehicle's data bus (for example CAN) or between control modules.
• Practical takeaway: U0137 indicates that a control module or multiple modules are failing to communicate reliably on the vehicle's data network. It is frequently accompanied by other U-codes or module-specific codes and may be intermittent or current only under certain operating conditions. The precise factory definition can vary by vehicle, so always cross-check with the vehicle's service information if available.
• Standard code information reference: GitHub repositories that define OBD-II codes typically classify U0137 as a network/communication fault. Use those definitions to confirm the code family and any manufacturer-specific interpretation when you have access to a factory-level code table.

Symptoms and user complaint patterns to expect

• General symptoms reported by users:
  • MIL or Service Light illuminated with a U0137 code; sometimes transient or intermittent
  • Multiple vehicle systems appear to "lose" communication (e.g., infotainment, ABS, HVAC, BCM/IPC visibility, dash instruments) while the engine ECU still appears operational
  • Scanning the vehicle reveals U0137 in addition to other U-codes or a subset of modular communication timeouts
  • Intermittent operation of modules that rely on data bus communication; some functions may appear normal at times, then drop out
• Realistic symptom descriptors you might use in the shop:
  • "Modules won't talk to each other" or "No data on the CAN bus"
  • "Some lights/dash readings go blank while driving, then come back"
  • "Error appears after battery disconnect, weather changes, or a fused accessory load
  • "Clear codes, but U0137 returns after a short drive or on cold starts"

Initial diagnostic considerations (what to check first)

• Confirm scope of the issue:
  • Is U0137 current (present on the latest drive) or historic (older data that no longer reappears)?
  • Are there other DTCs from the same or related networks? Look for U0100-U0199 (network/communications family) or module-specific codes (P, C, or other U codes) that point to a specific module or network segment.
• Safety and data collection:
  • Use a capable scan tool to read freeze frame data, identify which modules are reporting or not reporting, and note any time stamps or ignition states when the code set appears.
  • If possible, view module diagnostic pages and bus voltage status to understand if the network is being powered and terminated properly.

Step-by-Step Diagnosis

1) Verify the code and related data

• Confirm U0137 is current and not a one-time transient.
• Check for related U-codes (U0100, U0101, U0121, etc.) that indicate specific module communication failures.
• Review freeze frame data for engine/run state, vehicle speed, battery voltage, and other module activity at the time of the fault.

2) Inspect the basics of the vehicle's network and power

• Visually inspect major grounds and battery connections; ensure the battery is delivering stable voltage (12V nominal with minimal fluctuation) and that ground straps are clean and tight.
• Check fuses and fusible links related to the body/vehicle network control modules and the power distribution network.
• Confirm that key power supplies to the ECUs on the network are present and within spec.

3) Inspect wiring and connectors for the network

• Inspect CAN (or other network) high and low wires for damage, chafing, pinched sections, corrosion, or improper routing.
• Check for loose, corroded, bent, or pushed-out connectors at the modules involved in the network; reseat or replace as necessary.
• Look for aftermarket wiring, pig-tails, or damaged grounds that could introduce noise or intermittent connectivity on the data bus.

4) Identify affected modules and the network topology

• Use the scan tool to identify which modules are reporting data and which are not responding.
• If possible, map the modules that should be on the same network (CAN High/Low) and see which ones are failing to respond.
• Take note if the failure is centralized (e.g., one gateway or junction box) or distributed (multiple modules on the same bus show timeouts).

5) Check the physical layer of the bus

• Measure CAN High and CAN Low voltages with the ignition on and key off to assess differential bus stability. A healthy CAN differential while idling should show a stable voltage differential; large swings or no differential indicates a physical layer issue.
• Look for a fault in termination (usually 120-ohm resistor at each end of a CAN network); a missing, damaged, or incorrect termination can cause communication failures.

6) Module health and communication tests

• Attempt to ping or request data from modules that should be on the network; note which modules respond, which don't, and under what conditions.
• If possible, perform a module-specific diagnostic test (reflash/update, reseat connectors, or perform a factory communication test sequence per manufacturer guidance).
• If a single module consistently fails to communicate, consider module replacement or re-flash, bearing in mind the risk of cross-communication errors.

7) Look for software and calibration factors

• Some U0137 occurrences are related to software faults or corrupted ECU programs. Check for available software/firmware updates for the network modules or the vehicle's TCU/ECU ecosystem.
• If updates are available, perform the appropriate software update or reflash with the latest factory calibration in a controlled environment.

8) Validate fixes with a road test and recheck

• After any repair or reseating, clear codes and perform a controlled road test to verify that U0137 does not reappear.
• Re-scan after the test and confirm there are no new or persistent network-related codes.

Common Causes

Note: The following probabilities reflect general field experience and typical patterns seen with U-codes related to vehicle networks. The precise percentages may vary by vehicle make/model and the specific network architecture in use.

• Wiring, connectors, and grounds (physical layer issues on the data bus): 40-55%
  • Most U0137 cases stem from damage, looseness, corrosion, or poor routing of CAN/high-low wires and module connectors.
  • Loose grounds or compromised power grounds at one or more ECUs are a frequent contributor.
• Faulty or flaky modules (ECUs, gateways, BCMs, IPCs) and failed transceivers: 20-30%
  • A non-communicating module or a faulty bus transceiver can prevent data from propagating across the network.
  • Replacing or reseating the affected module(s) often resolves the problem.
• Power supply and battery/ground issues: 10-15%
  • Intermittent voltage dips or dropouts can cause modules to drop off the bus; stabilizing power often clears U0137.
• Software/firmware issues or corrupted bus configuration: 5-10%
  • Outdated or corrupted software may intermittently disable or misconfigure network communications; updating or reflashing modules can fix it.
• Other (rare) causes such as harness routing changes after repairs, improper aftermarket harness installations, or diagnostic tool interference: 0-5%
  • Ensure there are no aftermarket devices or wiring that disrupts the data bus.

Diagnostic Approach

• Confirm U0137 is current and note any related codes (especially other U-codes).
• Verify vehicle power stability: battery voltage within spec, no excessive voltage drop, and good grounds.
• Inspect and repair wiring/ connectors: CAN high/low wires, module connectors, grounds; fix corrosion and secure routing.
• Identify which modules are failing to communicate; confirm bus topology and termination integrity.
• Check for module-specific faults or updates; reseat or reflash as needed per manufacturer guidelines.
• Perform a controlled road test after repairs; re-scan and verify no reoccurrence.
• Document findings, repair actions, and verification results; if unresolved, escalate with OEM templates or advanced diagnostics (scope-level bus analysis).

Safety Considerations

• With network diagnostics, avoid shocking or damaging sensitive electronics. Always disconnect power when performing invasive wiring work, and follow proper ESD precautions.
• ABS/airbag/traction systems rely on precise, timely communication; do not perform invasive or unverified procedures that could deploy airbags or interfere with safety-critical modules.
• If your vehicle uses a high-voltage system or has special service procedures, follow the manufacturer's service guidelines and disconnect procedures.

Practical Tips

• Treat U0137 as an indicator of a network problem rather than a single-module fault until proven otherwise; the network is often a single root cause (ground/short/connector) that cascades into multiple module communication failures.
• If you have access to a high-quality oscilloscope or a CAN bus diagnostic tool, capture bus activity during engine start and at idle to look for abnormal voltage levels, bus stuffing, or arbitration problems.
• After repairs, always clear all codes, perform a test drive, and re-scan to ensure the issue does not recur. Document any new codes that appear and correlate them to the fix.

Appendix and references

• GitHub: Definitions and standard code information for OBD-II codes (used to confirm general meaning of U0137 and related U-codes)
• NHTSA complaints data (; if available, use to adjust probability weights)

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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