Comprehensive Diagnostic Guide: OBD-II Code U0248

Important Notes

• What U-codes are: In the OBD-II framework, codes are grouped into four families: P (Powertrain), B (Body), C (Chassis), and U (Network). U-codes indicate data-link/communication issues between control modules on the vehicle's network. OEMs often provide the exact definition of each U-code, and the precise meaning can vary by make/model. The general concept that U-codes relate to vehicle networking is described in the OBD-II references. See: Wikipedia - OBD-II: Diagnostic Trouble Codes; OBD-II: Powertrain Codes. These sources establish that DTCs include U-codes and that U-codes pertain to network/communication faults.
• OEM variability: The exact description of U0248 is not provided in the cited general sources. Therefore, for the definitive factory description and test procedures, refer to the vehicle's OEM service information or a manufacturer-specific diagnostic database.

Symptoms

• Illumination of the Malfunction Indicator Lamp (check engine light) with U0248 logged, sometimes alongside other U, P, or B codes.
• Intermittent or persistent loss of data between modules (e.g., cluster, BCM, PCM, TCM, ABS, or other control modules) leading to erratic gauge readings, missing dash information, or nonfunctional sub-systems.
• Modules failing to respond to diagnostic tool requests; multi-ECU "no communication" or sporadic communication errors.
• Drivability quirks that accompany network faults (e.g., inconsistent transmission behavior, cruise control enabling/disabling unexpectedly, or other module-dependent features behaving oddly).
• In some cases, diagnostic tool shows multiple CAN bus or data-link error frames on the vehicle's network.

What U0248 typically implies (context and limitations)

• U-codes denote network/communication issues on the vehicle's data bus (e.g., CAN). The exact description of U0248 is OEM-specific, so the primary implication is "a data-link / communication issue involving one or more ECUs." Because are general references, they describe the standard U-code category rather than the OEM's precise interpretation of U0248. Always confirm the OEM's specified description and test steps in service information for your vehicle.

Diagnostic outline (step-by-step) for U0248

1) Confirm scope and collect initial data

• Confirm the exact U0248 description from the OEM service information for the specific make/model/year.
• Record all DTCs present, freeze-frame data, and any pending/confirmed codes. Note any pattern (e.g., multiple modules failing to communicate together, or a single module repeatedly failing).
• Note vehicle condition and recent work (wiring repair, battery/alternator work, dashboard electronics, aftermarket electronics).

2) Visual and basic electrical checks

• Inspect the CAN (data-link) wiring harnesses for damage, chafing, or pin contamination at connectors. Look for loose, corroded, or bent pins; verify protection and routing.
• Inspect battery terminals and ground connections; check main grounds to the chassis and engine block for cleanliness and tightness.
• Check fuses and fusible links related to body/electrical modules and power supplies. A blown fuse or loose power feed can manifest as intermittent communications faults.
• Inspect for aftermarket devices or wiring that could be interfering with data lines (risk of unintended voltage or data disruption).

3) Power and ground integrity

• Verify battery voltage is stable (typical 12.6-14.8 V with engine running; confirm absence of voltage dips during load tests).
• Check for voltage spikes, drops, or poor ground paths that could affect ECU communication.
• If the vehicle uses a centralized power supply for network devices or a CAN transceiver, verify supply rails and ground references for those modules.

4) CAN data-link health and basic topology checks

• Using an appropriate scan tool, observe CAN bus activity and error counters if available (e.g., CAN high/low activity, error frames, or diagnostic trouble codes related to bus errors).
• If you have access to a CAN oscilloscope or equivalent, inspect CAN High (CAN-H) and CAN Low (CAN-L) differential signals for proper differential voltage levels, bus dominance, and clean recessive/dominant transitions. Look for excessive jitter, voltage offset, or short-to-B+ or short-to-ground conditions.
• Confirm there is no known wiring fault at connector interfaces (pin mapping, mis-matched connector mating, or inserted incorrect fuster spacing) that could create intermittent communications faults.

5) Module-by-module communication checks

• Identify which modules are expected to be on the same CAN network as the U0248 symptom. Attempt to ping/diagnose modules individually with OEM or compatible scan tools (example: BCM, PCM/ECM, TCM, Instrument Cluster, ABS/ESP, etc.).
• Check for modules that consistently fail to respond or report communication errors. Note if multiple modules fail to respond simultaneously, which strongly suggests a bus issue (wiring, connectors, terminations, or a shared supply).
• If possible, perform a controlled power-down/power-up sequence to observe if the fault is revived or cleared.

6) Software/firmware considerations

• Check for OEM service bulletins or updated firmware for networked modules that address communications or CAN bus reliability.
• If permissible, perform firmware updates or re-flash the relevant modules to the latest approved calibration. Ensure proper procedure and power protection during reflash.

7) Correlating data with vehicle operation

• Compare live data streams from modules; look for inconsistent or out-of-range values that originate from more than one module (e.g., modules reporting conflicting vehicle speed, RPM, or fault flags).
• Look for common failure patterns in the vehicle's diagnostics literature (OEM service information, TSBs) that connect U0248 to specific circuit issues or module interactions.

8) Narrowing down the fault source

• If a single module is consistently unresponsive or misbehaving, that module becomes the prime suspect. Check its wiring and power/ground supply, then recheck communications after repair or replacement.
• If many modules show communication issues, focus on the CAN bus network: harness, connectors, terminations, main power/ground rails, and vehicle-level network integrity (including any bridging modules or gateways).

9) Verification

• After repairs or replacements, clear codes and re-run the vehicle through the same scenarios to verify that communications are restored and that U0248 (and any related codes) do not reappear.
• Validate that all primary systems requiring network communication function correctly (e.g., instrumentation, transmission control, ABS/traction, engine management, body electronics).

Common Causes

• CAN bus wiring/connectors issues (loose connectors, damaged harness, corrosion, routing problems): high probability due to the central role of the network in module communication. Estimated contribution: 25-40%.
• Faulty or intermittent module(s) on the network (ECM/PCM, BCM, TCM, Instrument Cluster, ABS module, etc.) failing to communicate or providing corrupt data: moderate probability depending on vehicle; estimated contribution: 20-30%.
• Electrical power/ground issues (battery, alternator, poor grounds, sudden voltage dips during load): common root cause for intermittent communications; estimated contribution: 10-20%.
• Software/firmware issues or calibration mismatches in networked modules: less frequent but plausible, especially after recent updates or programming; estimated contribution: 5-15%.
• Signal integrity problems (short to power/ground, resistor/terminator faults on the network, EMI sources): less common but possible; estimated contribution: 5-10%.

Tools and data you'll want

• A capable OBD-II scan tool that supports CAN and can log live data, view multi-ECU communication, and read OEM or enhanced diagnostic data.
• OEM service information resource or a compatible diagnostic software package to access specific U-code definitions and procedures for the vehicle.
• A digital multimeter (DMM) for voltage and resistance checks; a scope or CAN bus diagnostic tool for waveform analysis if available.
• Physical inspection tools for wiring and connectors; basic hand tools for connector reseating and harness repair.
• Service bulletins and updates from the vehicle manufacturer.

Notes on emissions and safety

• U-codes generally reflect communication network health rather than emissions-critical sensor faults; however, network faults can contribute to drivability and may affect emissions readiness indirectly if miscommunications prevent proper sensor data from being used for control. The Wikipedia sources indicate the DTC framework and the separation of diagnostic categories; OEMs may have specific emission-related implications for network faults in certain models.
• Exercise standard safety precautions when inspecting or probing electrical systems: disable devices as appropriate, avoid shorting power rails, and follow the vehicle's service procedures for battery disconnects or module reprogramming.

Summary and practical outlook

• U0248 is an OBD-II network/communication DTC. The exact OEM description for U0248 is vehicle-specific, so rely on OEM service information for the precise fault description and test steps.
• The diagnostic approach should focus on the health of the CAN/data-link network, hardware integrity of wiring and connectors, power/ground stability, and the health of critical ECUs on the bus.
• Expect to verify by collecting live data traces, confirming communications with key modules, applying targeted wiring/ground repairs if needed, and updating module firmware if recommended by the OEM.
• After resolving the root cause, clear codes, test drive to confirm stability, and ensure no new DTCs reappear.

References (consistent with )

• OBD-II diagnostic trouble codes and the four-category scheme (P, B, C, U) and the Diagnostic Trouble Codes sections. These sources establish that U-codes represent network/communication faults rather than purely powertrain or body/Chassis functional faults. See: Wikipedia - OBD-II, Diagnostic Trouble Codes; OBD-II - Powertrain Codes; OBD-II - Emissions Testing. These pages establish the coding framework and the role of DTCs in modern vehicles.
• For standard code definitions and the general concept of U-codes, the broad framework is provided by the OBD-II overview in . If you need the exact factory description for U0248, consult the vehicle's OEM service information or a manufacturer-specific diagnostic resource.

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.

---