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Home / DTC / U1301 — Lost Communication on Serial Data Bus

U1301 — Lost Communication on Serial Data Bus

Detailed page for trouble code U1301.

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U1301

Generic U — Network/User

Lost Communication on Serial Data Bus

Brand: Generic
Type: U — Network/User
Views: UK: 0 EN: 1 RU: 1
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Page language: EN

Causes

  • Intermittent or low battery/charging system voltage
  • Open, short or high-resistance condition in serial bus wiring or connectors
  • Corroded, loose or damaged module connector
  • Failed or malfunctioning control module on the bus
  • Missing or incorrect bus termination resistor(s)
  • Software/version mismatch after module replacement or update

Symptoms

  • One or more control modules report ‘no communication’ or are not present in scan tool
  • Multiple dashboard warning lights or message center errors
  • Loss of specific vehicle functions controlled by the missing module(s) (e.g., ABS, transmission, climate)
  • Intermittent faults that may clear with ignition cycles or reconnecting connectors
  • Failure to communicate with module when connected with a scan tool

What to check

  • Use a manufacturer-capable scan tool to confirm U1301, record freeze frame and active/inactive status of related codes
  • Check battery voltage and charging system; ensure stable >12.4 V (engine off) and proper charging when running
  • Visually inspect wiring harnesses and connectors along the bus for damage, corrosion, water ingress or repairs
  • Verify power and ground at each module on the affected bus with a meter
  • Check for aftermarket electronics (alarms, stereo, modules) tied into the bus and temporarily disconnect them
  • Check for relevant TSBs or software updates for communication issues

Signal parameters

  • Bus idle voltage and reference levels (single-wire LIN or differential CAN high/low voltages)
  • Dominant and recessive levels for CAN (typical CAN_H ≈ 2.5–3.5 V, CAN_L ≈ 1.5–2.5 V; differential ~2 V)
  • Presence and frequency of messages / frames for target module IDs using a scan tool or bus analyzer
  • Oscilloscope waveform shape (clean square/edges) and absence of excessive noise or reflections
  • Bus load/resistance between CAN_H and CAN_L (typical ≈ 60 Ω for two 120Ω terminations)
  • CRC/checksum and message error counters reported by modules

Diagnostic algorithm

  1. Verify code with scan tool and note which modules are not communicating. Save freeze frame and live data.
  2. Check battery and charging voltage; ensure stable supply during diagnostics. Recharge or replace battery if voltage is low.
  3. Clear codes and attempt to reproduce; note if U1301 returns steady or intermittently.
  4. Inspect connectors and wiring along the affected bus visually and through gentle wiggle tests while watching the scan tool for changes.
  5. Identify bus topology via wiring diagram; locate and measure termination resistors and measure resistance between bus high and low (expect ~60Ω on CAN with both terminations).
  6. Probe bus with oscilloscope or lab-grade scan tool to view waveform quality, bit timing and message presence. Look for missing IDs, noise, or dominant stuck lines.
  7. Verify power and ground at each module on the bus. If a single module power/ground is missing or intermittent, repair that circuit and retest.
  8. If a specific connector or splice is suspect, disconnect the module and measure bus behavior; disconnect the module from the bus and see if bus restores normal communication (isolate faulty module).
  9. Disconnect aftermarket devices that tie into the bus. Re-test communication.
  10. If wiring checks are OK and a particular module appears at fault, consult OEM diagnostics for module reprogramming or bench testing, and consider module replacement only after confirming failure.
  11. After repairs, clear DTCs and verify stable operation over drive cycles; confirm no recurrence and that all dependent functions are restored.

Likely causes

  • Wiring fault or connector corrosion on the affected data bus
  • Failed control module that has stopped sending/receiving messages
  • Low battery or intermittent supply/ground to one or more modules
  • Improper termination (open/missing resistor) or short to power/ground caused by damage or aftermarket accessory

Fault status

⚠️ Status
U1301 — The vehicle serial data bus has experienced loss of communication. One or more modules are not sending or receiving expected network messages; fault may be intermittent or permanent.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0100 U0121 U0140 U0073 U1000
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