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Home / DTC / U0001 — High Speed CAN Communication Bus | CAN Bus OFF | TCU Communication Line or TCU Error | CAN Communication Malfunction | CAN Communication Bus Off | CAN BUS OFF | High Speed CAN Communication Bus off (C-CAN) | High Speed CAN Communication Bus (C-CAN)

U0001 — High Speed CAN Communication Bus | CAN Bus OFF | TCU Communication Line or TCU Error | CAN Communication Malfunction | CAN Communication Bus Off | CAN BUS OFF | High Speed CAN Communication Bus off (C-CAN) | High Speed CAN Communication Bus (C-CAN)

Detailed page for trouble code U0001.

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U0001

HYUNDAI U — Network/User

High Speed CAN Communication Bus | CAN Bus OFF | TCU Communication Line or TCU Error | CAN Communication Malfunction | CAN Communication Bus Off | CAN BUS OFF | High Speed CAN Communication Bus off (C-CAN) | High Speed CAN Communication Bus (C-CAN)

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

Causes

  • Short circuit (CAN_H or CAN_L) to battery voltage or ground
  • Open or shorted CAN bus wiring or damaged harness
  • Poor or corroded connector pins at TCU or other modules
  • Failed TCU or other control module driving the bus
  • Missing or incorrect termination (open or shorted 120 Ω resistors)
  • Low battery voltage or unstable power supply to modules

Symptoms

  • MIL (Check Engine) or transmission-related warning lamp illuminated
  • No response to transmission commands; gear selection issues or limp mode
  • Scan tool shows TCU not present / no communication with TCU
  • Other modules reporting network errors or multiple U‑codes
  • Intermittent or permanent loss of transmission data (RPM, gear, temp)
  • Inability to perform some diagnostic/actuator tests on TCU

What to check

  • Use a capable scan tool to read U‑codes and list modules present on C‑CAN
  • Visually inspect CAN wiring and connectors for damage, corrosion, or pin push‑out
  • Check battery voltage (engine off and cranking) and module power/ground circuits
  • Measure resistance across CAN_H and CAN_L with ignition OFF — typical network ≈ 60 Ω
  • Check for short to battery or ground by measuring continuity from each CAN line to B+ and to chassis
  • Probe CAN_H and CAN_L with oscilloscope or lab scope with ignition ON and engine cranking to view waveform

Signal parameters

  • High‑speed CAN typical baud rate: 500 kbps (confirm factory spec for vehicle)
  • Idle (recessive) voltage: ~2.5 V on CAN_H and CAN_L (each to ground)
  • Dominant state: CAN_H ~3.5 V, CAN_L ~1.5 V (differential ≈ 2.0 V)
  • Bus termination: two 120 Ω resistors in parallel → measured ≈ 60 Ω across CAN_H–CAN_L with ignition OFF
  • Short to B+ will pull line toward battery voltage; short to ground will pull toward 0 V

Diagnostic algorithm

  1. Connect a factory‑capable scan tool. Record stored codes, freeze frame, and list modules present on C‑CAN.
  2. Verify battery and module power/ground voltages. Repair any low supply or poor ground before further network tests.
  3. With ignition OFF, measure resistance between CAN_H and CAN_L at a convenient connector near TCU; expect ≈ 60 Ω. If open or very low, suspect termination or short.
  4. Inspect and backprobe TCU CAN pins and nearby harness for corrosion, pin damage, or water ingress. Repair connectors as needed.
  5. With ignition ON (engine off), monitor CAN_H and CAN_L with an oscilloscope or CAN bus analyzer. Look for healthy differential waveform or a line stuck dominant/recessive and bus errors.
  6. If waveform abnormal, isolate sections of the network: disconnect modules or segments one at a time (start with recent repairs or accessories) while watching bus status to identify the node causing bus off.
  7. Check for shorts to B+ or ground on each CAN conductor. Repair wiring harness faults or shorts.
  8. If a single module (e.g., TCU) is suspected, connect known‑good module or bench test transceiver if available. Replace only after isolating fault to the module.
  9. Update module software if manufacturer bulletin or reflash procedure is available and recommended.
  10. After repair, clear codes and verify stable communication, correct termination, and normal drivability during road test.

Likely causes

  • Damaged CAN wiring harness near transmission or junction points
  • Faulty or corroded connector at TCU (pin damage/poor contact)
  • Short to B+ or ground on CAN_H or CAN_L from a chafed wire
  • Failed TCU transceiver or another node holding bus dominant
  • Missing/failed termination resistor (open or shorted)

Fault status

⚠️ Status
High‑speed CAN (C‑CAN) bus off — TCU not communicating on the high‑speed CAN network. Possible wiring short/open, bad termination, faulty TCU or another node driving the bus dominant. Verify power/ground, inspect wiring/connectors, and isolate faulty node.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0073 U0100 U0121 U0141 P0700
371

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