Comprehensive Diagnostic Guide for OBD-II Code U0147

Important Notes

• U0147 is a network/communication fault code in the OBD-II framework. U-codes are used to indicate data transmission problems on vehicle networks (CAN/LIN/FlexRay, etc.). In many vehicles, U0147 specifically relates to loss of data from the Steering Assist Sensor or Steering Control/Assist network. OEM implementations vary, so confirm with the vehicle's service information for model-specific definitions and recalibration procedures. This framing aligns with general OBD-II documentation that U-codes represent network communication faults. See: OBD-II Diagnostic Trouble Codes and related Powertrain Codes references.
• Because U0147 is a network code, root causes are commonly CAN bus or module-related rather than a single sensor fault. The general symptom pattern and diagnostic approach below emphasize network health, module communications, and steering-related subsystems.

Symptoms

• Steering-related warning lights come on (EPS/Steering Service, ABS/DSC indicators may accompany or be affected).
• Steering feels heavy, inconsistent, or intermittently fails to provide assist; in some cases, steering may feel normal until the code reappears.
• Cruise control or lane-keeping features may behave unexpectedly or be degraded due to network data loss.
• Intermittent steering-related faults that occur with vehicle start-up, varying with engine state or battery condition.

Preliminary notes on access and data

• Start with a reliable, capable scan tool that can read current DTCs, freeze-frame data, live CAN data, and, if possible, OEM-specific data streams for steering and gateway modules.
• Record all active codes, pending codes, freeze-frame data, and any related U or P/B/C codes. If U0147 appears with other CAN/network codes (for example U0100, U0101, U0121, P-codes, etc.), the fault is more likely a CAN bus issue or gateway fault rather than a single sensor fault.
• Check vehicle power (battery voltage) and grounding, as low voltage can cause intermittent CAN messaging issues and misreads on steering-related nodes.

What U0147 typically points to (conceptual overview)

• Lost or corrupted communication on the steering network between the Steering Control Module, Steering Assist Sensor (SAS), EPS, or gateway/c gateway modules.
• The exact module reporting or failing to receive data can vary by OEM, but the underlying problem is data not being delivered or received on the steering-related CAN network.

Probable Causes

• Faulty or out-of-calibration Steering Angle Sensor (SAS) within the steering column or steering gear assembly: 25-45%
• Steering Control Module (SCM) or EPS unit fault or software/firmware issue: 15-25%
• CAN gateway/central gateway module or vehicle network gateway fault: 15-25%
• Damaged, corroded, or loose CAN bus wiring, connectors, or harnesses in the steering network path (including connectors at the SCM, EPS, SAS, gateway, or instrument cluster): 10-20%
• Battery voltage instability or grounding issues affecting CAN communications (including high-current events or grounding faults): 5-10%
• OEM software/Calibration issues or required updates (recalibration of SAS, SPS, or gateway software): 5-15%
• Other modules on the CAN bus blocking or misrouting messages (ECU interaction conflicts): 5-10%

Note on data sources

• The above framework is consistent with general OBD-II concepts that U-codes are network/communication faults. Specific U0147 behavior and troubleshooting steps can vary by vehicle make/model; consult OEM service information for exact definitions and recalibration procedures.

Diagnostic Approach

1) Verify and document

• Confirm U0147 is active with current codes. Note whether it is accompanied by other CAN/network codes (U0100, U0101, U0121, etc.), P/B/C codes, or if it is the sole code.
• Review freeze-frame data for voltage, battery state of charge, engine RPM, vehicle speed, and other live data around the time the code was set.
• If available, pull OEM/vehicle-specific data for steering network (SAS data, steering torque, wheel angle, EPS status, gateway data rates).

2) Inspect power, grounds, and battery health

• Check 12V battery voltage with engine off and with engine running; ensure stable voltage (typically 12.5-12.8V resting; 13.5-14.5V while running).
• Inspect main vehicle grounds and critical engine/steering grounds. Poor grounding can cause intermittent CAN faults.
• Inspect fuses related to CAN power rails, steering modules, EPS, SAS, and gateway. Replace any blown fuses and reseat connectors.

3) Inspect CAN network health and physical integrity

• Visually inspect the steering network harnesses and connectors for signs of damage, corrosion, moisture ingress, bent pins, or loose connections at:
  • Steering Control Module (SCM)/EPS harness
  • Steering Angle Sensor (SAS) connector (often located in the steering column)
  • Central Gateway or CAN gateway module
  • Instrument cluster and other body/electrical modules on the same CAN backbone
• Inspect for pin damage or mis-seated connectors; reseat and clean connectors as needed; apply dielectric grease to moisture-prone connectors if recommended by OEM.

4) Analyze CAN bus electrical behavior (if equipped)

• Using a multimeter or oscilloscope, verify CAN High and CAN Low integrity at relevant harness points:
  • Commonly, CAN signals ride in the 2.5V-ish range with differential signaling; look for proper differential voltage when the bus is idle and when messages are transmitted.
  • A stuck or missing CAN High/Low signal, excessive resistance, or shorts to power/ground can indicate wiring issues.
• If possible, monitor live CAN data streams for SAS/Steering-related messages and gateway activity to determine if messages are being transmitted and forwarded as expected.

5) Check for software/Calibration requirements

• Verify if there are any OEM service bulletins or software updates addressing steering network communication or SAS calibration for the model-year in question.
• If the OEM requires a SAS calibration, perform it using the appropriate service procedure and tools.
• Ensure vehicle software is up to date on all involved modules (SCM/EPS, SAS, gateway). Reflash/update if addressed by OEM.

isolate the steering components (guided testing)

• If you have access to OEM-level diagnostics or a capable test tool:
  • Read SAS angle data and compare to wheel angle; confirm consistency within expected tolerances.
    If SAS data is not being reported to the EPS or gateway, focus on SAS harness/connectors and the SAS itself.
• Consider a controlled test: with key on, observe which modules communicate on the CAN bus. If the steering network messages stop being observed at a gateway or SCM when the steering angle changes, suspect the SAS or the gateway path.

targeted component testing and replacement strategy

• SAS (Steering Angle Sensor):
  • Symptoms: inconsistent steering data, misalignment with wheel angle, calibration drift.
  • Action: replace SAS if confirmed faulty or if calibration cannot be achieved; perform SAS calibration/relearn after replacement if required by OEM procedure.
• EPS/SCM:
  • Symptoms: steering assist intermittently fails or is unavailable; EPS warning present.
  • Action: inspect and, if necessary, replace or reflash the EPS/SCM; verify calibration and communications post-repair.
• CAN Gateway / Gateway module:
  • Symptoms: multiple CAN-related faults; other modules on CAN backbone show abnormal behavior.
  • Action: check gateway power, ground, and data lines; reflash or replace gateway if OEM procedure calls for it; verify communications after repair.
• Wiring harness and connectors:
  • Action: repair damaged wiring, replace connectors, reseat, and re-torque as specified; re-check for corrosion or moisture ingress.
• Battery/ground issues:
  • Action: correct charging system or grounds that could cause intermittent CAN messaging.

8) Verification and validation

• After any repair, clear all codes and perform a thorough road test under various conditions (cold start, warm start, steering lock/unlock scenarios, varying speeds).
• Re-scan to verify U0147 does not return and that related CAN codes remain clear.
• If U0147 reappears, re-evaluate for intermittent harness faults, poor ground, or a latent ECU issue; consider a deeper OEM-guided diagnostic path or dealer diagnostic service.

Repair quality notes

• Because U0147 points to a network communication fault, the root cause is commonly a CAN bus or gateway/ECU issue rather than a single sensor fault. Prioritize network health and steering subsystem integrity.
• Recalibration or re-learn procedures (for SAS, steering angle, or gateway recalibration) are an important part of the repair in many OEMs; perform them if the OEM procedure requires it.
• If replacing components, ensure software/firmware levels are compatible and that any required adapters or vehicle-specific calibration sequences are followed.

Documentation template (what to record after repair)

• Codes observed before and after repair.
• Freeze-frame data at the time of failure.
• Battery voltage, charging system status, and ground integrity readings.
• Steps taken (visual inspection, wiring checks, connector reseating, fuses, software updates, SAS calibration, component replacement).
• OEM service bulletin references or software level changes used.
• Road test notes: steering feel, reliability, and any warnings observed.

Safety Considerations

• Disconnecting or servicing steering-related modules, SAS, or EPS can impact steering control. Follow OEM procedures and use appropriate safety precautions.
• Avoid rapid forceful maneuvers or aggressive road testing if steering feel is degraded; ensure the vehicle is safely test-driven in controlled conditions.
• When working around airbag systems or steering-column components, observe standard safety precautions to avoid accidental deployments or injury.

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.

---