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Home / DTC / U0029 — Vehicle Communication Bus A Performance

U0029 — Vehicle Communication Bus A Performance

Detailed page for trouble code U0029.

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Code

U0029

HYUNDAI U — Network/User

Vehicle Communication Bus A Performance

Brand: HYUNDAI
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Damaged or chafed CAN wiring (short to ground, short to battery, or open)
  • Corroded, loose, or poor connector pin contact on CAN wires or module connectors
  • Failed CAN transceiver(s) in one or more control modules
  • Missing or incorrect termination (open or shorted 120 Ω resistors)
  • High coupling noise or excessive EMI on the bus (aftermarket electronics, poor routing)
  • Low battery/charging system problems causing unstable bus voltages

Symptoms

  • Multiple communication-related DTCs in different modules (e.g., lost comm with ECM, ABS, clusters)
  • Instrument cluster warnings, inoperative gauges or lamps, or blank display
  • Intermittent or permanent no-start or limp mode if ECM loses bus data
  • Loss of specific functions controlled by modules on Bus A (doors, HVAC, ABS, traction control)
  • Erratic module behavior (random resets, flickering displays)
  • MIL or network warning lamp illuminated

What to check

  • Use a scan tool to read U0029 plus all stored/active DTCs in every module; note freeze frame and timestamps
  • Visually inspect CAN wiring and connectors along the bus for damage, corrosion, or aftermarket splices
  • Check battery condition and charging system voltage (stable ~12.6 V at rest, ~13.5–14.8 V running)
  • Measure resistance between CAN_H and CAN_L at two ends of the bus — expected ~60 Ω (two 120 Ω terminators in parallel)
  • Backprobe CAN_H and CAN_L with an oscilloscope to inspect waveform for clean differential signals and expected bit timing
  • Use a DC multimeter to check for shorts: CAN_H to battery, CAN_L to battery, CAN_H to ground, CAN_L to ground

Signal parameters

  • CAN bus recessive state: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (differential ≈ 0 V)
  • CAN bus dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
  • Typical transceiver VCC (logic) ≈ 5 V (verify vehicle-specific values)
  • Bus termination: two 120 Ω resistors in parallel ≈ 60 Ω between CAN_H and CAN_L
  • Common data rates: 250 kb/s or 500 kb/s depending on vehicle subsystem — waveform timing should match expected baud

Diagnostic algorithm

  1. Clear codes and attempt to reproduce; record conditions and any recurring patterns.
  2. Use scan tool to list all U-codes and module failures; identify which modules report loss of communication on Bus A.
  3. Visually inspect entire CAN Bus A wiring harness and connectors; repair obvious damage.
  4. With ignition ON, measure DC voltages at several CAN nodes: check that CAN_H and CAN_L sit near 2.5 V (recessive) and that VCC and ground to modules are correct.
  5. Measure end‑to‑end bus resistance between CAN_H and CAN_L at two service points; expect ≈60 Ω. If abnormal, locate open or shorted termination(s).
  6. Use an oscilloscope to capture CAN_H and CAN_L waveforms while bus traffic occurs; look for missing dominant/recessive transitions, excessive noise, reflections, or clipped signals.
  7. Isolate the fault by disconnecting modules or aftermarket devices one at a time (follow manufacturer safety procedures); note when bus performance returns to normal.
  8. Repair wiring, connectors, or replace failed module/transceiver as identified. Replace or restore proper termination resistors if necessary.
  9. After repair, clear codes, re-scan all modules, and perform a road test under conditions that previously produced the fault to confirm repair.
  10. If intermittent and cannot be reproduced, consider harness reroute, improved grounding, or adding shielding only per manufacturer guidance.

Likely causes

  • Wire harness damage near wheel wells or underbody (common failure points)
  • Faulty or contaminated connector at a module on CAN Bus A
  • Failed CAN transceiver in a commonly failing module (ECU, BCM, instrument cluster)
  • Incorrect or missing termination resistor(s) after collision repair or aftermarket installs
  • Aftermarket device connected to the bus creating excessive load or noise

Fault status

⚠️ Status
Vehicle Communication Bus A Performance — data frames degraded or lost on CAN Bus A causing module communication faults.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 2.0-4.0 hours

Similar codes

U0100 U0073 U0101 U0115 U0140 U0121
371

Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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