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Home / DTC / U1300 — In-vehicle network communication malfunction

U1300 — In-vehicle network communication malfunction

Detailed page for trouble code U1300.

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U1300

Generic U — Network/User

In-vehicle network communication malfunction

Brand: Generic
Type: U — Network/User
Views: UK: 0 EN: 6 RU: 2
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Page language: EN

Causes

  • Intermittent or permanent wiring damage on a vehicle data bus (CAN/LIN/FlexRay etc.).
  • Failed or intermittent control module (ECU) on the network.
  • Poor ground or power supply to one or more modules affecting bus drivers.
  • Missing or incorrect termination resistor(s) on the bus.
  • Aftermarket electronics or modules interfering with the bus.
  • Corroded or loose connectors at modules or junctions.

Symptoms

  • Illumination of network/communication-related warning lights (e.g., ABS, traction, airbag, check engine).
  • Loss of functionality of one or more modules (e.g., no instrument cluster data, HVAC not responding).
  • Intermittent or continuous diagnostic trouble codes related to multiple modules.
  • Multiple modules report ‘no communication’ or ‘bus off’.
  • Unreliable or lost data on scan tool live-data screens for certain modules.

What to check

  • Connect a capable scan tool and record all stored and pending U-codes and related module errors. Note which modules report communication loss.
  • Check battery voltage and test charging system; ensure stable 12V supply under key-on and cranking.
  • Visually inspect wiring harnesses, connectors, and junctions along the affected bus for damage, corrosion, or rodent chew.
  • Check module ground points and power feeds for continuity and secure mounting.
  • Verify presence and value of bus termination resistors (typical CAN total ~60 ohms across CAN_H and CAN_L).
  • If available, use an oscilloscope to observe bus signal waveforms; check for dominant/recessive levels and noise.

Signal parameters

  • CAN bus idle (recessive) voltages: both CAN_H and CAN_L ≈ 2.5 V (each).
  • Dominant state typical voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V).
  • Differential voltage (CAN_H minus CAN_L): ~0 V (recessive) to ~2 V (dominant).
  • Termination resistance measured across CAN_H and CAN_L: approx. 60 Ω (two 120 Ω terminators in parallel).
  • Bus continuity: no open circuit across branches; low resistance to allow proper signaling.
  • Module supply voltage: stable battery voltage (approximately 12–14.5 V) with key on and during cranking.

Diagnostic algorithm

  1. Record all codes with a scan tool; note which modules are offline and whether the code is present on multiple modules.
  2. Verify battery and charging system health; confirm stable supply voltage while recreating the fault.
  3. Inspect visible wiring and connectors for damage, corrosion, or loose pins—repair any faults found.
  4. Identify which physical bus is affected (CAN1, CAN2, LIN, etc.) by correlating modules reporting faults.
  5. Check and measure termination resistance across the bus wiring near the junction points (expect ~60 Ω for CAN).
  6. Backprobe CAN_H and CAN_L at a convenient connector and measure idle voltages; look for stuck-high/low or abnormal differential.
  7. Use an oscilloscope (preferred) to watch bus waveforms while exercising modules; look for noise, reflections, missing edges, or stuck dominant.
  8. Perform a wiggle/strain test on harness sections and connectors while monitoring bus to locate intermittent faults.
  9. Disconnect suspected module(s) or aftermarket devices one at a time (with key off unless specified) to see if the bus returns to normal.
  10. If a module transceiver is confirmed faulty or wiring is irreparably damaged, repair or replace the module or wiring harness as required.
  11. After repairs, clear codes and perform a functional test and road test to verify the issue is resolved; re-scan for recurrence.

Likely causes

  • Open or shorted CAN_H or CAN_L wires, or short to battery/ground.
  • Failed transceiver inside a control module causing bus errors.
  • Poor chassis ground or low battery voltage under load producing communication loss.
  • Failed bus termination (missing or high resistance), causing reflections and errors.
  • Connector corrosion at gateway/junction or a damaged splice on the bus harness.

Fault status

⚠️ Status
U1300 — Network communication malfunction: the vehicle has detected communication errors on an in-vehicle data bus. This indicates messages are not being exchanged reliably between modules; further diagnosis is required to locate the failing module, wiring, or termination problem.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3.0 hours

Similar codes

U0073 U0100 U0113 U0121 U0140 U1277
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