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Home / DTC / U1073 — Bus-Off

U1073 — Bus-Off

Detailed page for trouble code U1073.

34,332codes
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22,491specific
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U1073

MITSUBISHI U — Network/User

Bus-Off

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

Causes

  • Short or intermittent short to battery or ground on CAN_H or CAN_L wiring
  • Open or high-resistance connection in CAN bus wiring or connectors
  • Missing, damaged or incorrect termination (120 Ω at each end)
  • Faulty ECU/module or transceiver sending corrupted frames
  • Low battery or unstable vehicle supply voltage
  • Water intrusion/corrosion in connectors or harness damage

Symptoms

  • Loss of communication with one or more modules (module MILs, blank modules on scanner)
  • Multiple network-related DTCs present or reappearing after clearing
  • Certain systems inoperative or limp mode for affected modules
  • No or intermittent CAN messages seen on scan tool
  • Difficulty waking or programming modules
  • Battery drain or unexpected resets in some cases

What to check

  • Read all stored and pending network DTCs on all modules; note timestamps and repeating patterns
  • Check battery voltage and charging system before network tests (stable ~12.6 V at rest)
  • Visually inspect CAN wiring, connectors, and grounding points for damage, corrosion, pin push-out, or rodent chewing
  • Check for correct termination: measure resistance between CAN_H and CAN_L with ignition off (approx. 60 Ω with both 120 Ω terminators present)
  • Use scan tool to monitor CAN bus traffic and verify which nodes are present and which drop off
  • If available, use oscilloscope to view CAN_H and CAN_L waveforms for noise, dominant/recessive levels, and transceiver behavior

Signal parameters

  • CAN bus idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (typical range ±0.3 V)
  • CAN bus dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V ±0.5 V)
  • Termination resistance (ignition off, between CAN_H and CAN_L): ≈ 60 Ω (two 120 Ω terminators in parallel)
  • No-load continuity: near infinite between each CAN line and chassis ground (no shorts)
  • Expected presence: repeated CAN frames from each module when bus healthy (verify with bus traffic counters)

Diagnostic algorithm

  1. Record all U- and network-related DTCs from every module and note which modules report communication loss.
  2. Verify vehicle battery/charging system and ensure stable supply voltages before testing network.
  3. Visually inspect CAN harness, connectors, and terminators for damage or corrosion. Repair obvious wiring faults.
  4. Measure termination resistance between CAN_H and CAN_L (ignition off). Replace missing/damaged terminators to obtain ≈60 Ω.
  5. With scan tool, observe live bus traffic. Note which node(s) stop transmitting or show errors. If bus is dead, proceed to physical-layer checks.
  6. Use a lab scope on CAN_H and CAN_L to inspect waveforms for noise, clipped edges, stuck dominant, or asymmetric levels. Compare to expected signal_params.
  7. Isolate the fault by disconnecting modules one at a time (ignition off) or by sectioning the harness to find the node or segment causing errors. After each change, clear codes and re-test.
  8. If a suspect module is identified, swap with a known-good module (if available) or bench-test the module/transceiver per manufacturer procedures.
  9. Repair or replace damaged wiring, connectors, or module as indicated. Reinstall correct termination and secure grounds.
  10. Clear codes, verify normal bus traffic, and road-test to ensure the Bus-Off event does not recur. If intermittent, perform extended monitoring with data logger.

Likely causes

  • Damaged wiring or connector causing intermittent short/ground
  • Missing or incorrect termination resistor(s)
  • Faulty ECU or CAN transceiver generating repeated errors
  • Low or unstable vehicle voltage causing communication faults
  • Corroded connectors allowing intermittent signals

Fault status

⚠️ Status
Bus-Off means a node’s CAN controller has disabled its transmitter after exceeding internal error thresholds. The affected module stops sending messages until the controller is reset or the fault condition is removed. This generally indicates a serious physical-layer problem, a faulty transceiver, or repeated protocol errors.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

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