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Home / DTC / U0071 — Vehicle Communication Bus E (-) High

U0071 — Vehicle Communication Bus E (-) High

Detailed page for trouble code U0071.

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Code

U0071

HYUNDAI U — Network/User

Vehicle Communication Bus E (-) High

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

Causes

  • Short to battery positive or another high voltage source on the Bus E negative conductor
  • Damaged or corroded wiring or connector on the Bus E negative circuit
  • Faulty or failed CAN/LIN transceiver in a module connected to Bus E
  • Incorrect or missing termination (resistor) causing abnormal voltage
  • Poor or missing ground(s) affecting bus reference voltage
  • Water ingress or contamination in connectors

Symptoms

  • Multiple control modules on Bus E show communication faults or go into limp mode
  • Malfunction Indicator Lamp (MIL) or multiple dashboard warning lights
  • Loss of specific functions controlled via Bus E (may be intermittent)
  • Inability to communicate with one or more modules with a scan tool
  • Modules present but showing erratic data or stale/inaccurate values

What to check

  • Read and record freeze frame and all U-codes with a scan tool; note affected modules
  • Visual inspection of Bus E wiring, connectors, and grounds for damage or corrosion
  • Backprobe and measure bus voltages (Bus E + and -) with key ON, engine OFF
  • Measure resistance across the bus pair (expected ~60 ohms with proper termination)
  • Disconnect suspect modules one at a time to see if the fault clears (isolate faulty module)
  • Use an oscilloscope to view bus waveforms for noise, stuck high/low, or transients

Signal parameters

  • Recessive (idle) voltage: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each wire around 2.5 V)
  • Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
  • Typical bus differential (recessive): ~0 V; (dominant): ~2 V
  • Termination: two 120 ohm resistors in parallel ≈ 60 ohms across the bus pair
  • For this fault expect CAN_L (Bus E -) measured substantially higher than ~2.5 V (above specification) or stuck near battery voltage if shorted

Diagnostic algorithm

  1. Connect a dealer-level or full-function scan tool. Retrieve and document U0071 and any related codes or freeze frame data.
  2. Perform a visual inspection of Bus E harness routing, connectors, and control modules for damage, corrosion, aftermarket taps, or water intrusion.
  3. With ignition ON (engine OFF), backprobe the Bus E positive and negative wires at a convenient connector. Measure voltages to ground and between the pair. Compare to expected (see signal_params).
  4. Measure resistance across the bus pair with power off. Expect roughly 60 ohms. Infinite or very low values indicate open or short conditions respectively.
  5. If CAN_L (Bus E -) is high, disconnect modules on Bus E one at a time (or disconnect suspected connectors/splices) and recheck the bus voltage after each disconnect to isolate the offending module/harness section.
  6. Use an oscilloscope to inspect waveforms while the bus is connected. Look for stuck high/low signals, noise, or improper dominant/recessive transitions.
  7. If a specific module is identified as causing the condition, verify its grounds and power pins, inspect and repair the wiring or connector, then re-test. Replace module only after wiring and termination have been confirmed good.
  8. After repair, clear codes, perform functional tests and road test to confirm the fault does not return.

Likely causes

  • Pinched or chafed Bus E negative wire shorted to a power feed
  • Disconnected or failed bus termination resistor(s)
  • One module on Bus E driving the low side incorrectly (failed transceiver)
  • Corroded connector at a module or splice raising bus voltage
  • Damaged harness after recent repair or collision

Fault status

⚠️ Status
Vehicle Communication Bus E (-) voltage above allowable threshold; communication on Bus E impaired.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0073 U0100 U0101 U0121 U0155
371

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