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Home / DTC / U0033 — Vehicle Communication Bus A (-) Open

U0033 — Vehicle Communication Bus A (-) Open

Detailed page for trouble code U0033.

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Code

U0033

HYUNDAI U — Network/User

Vehicle Communication Bus A (-) Open

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

Causes

  • Broken or chafed CAN L wiring or damaged insulation
  • Loose, corroded or disconnected connector/pin at a control module or splice
  • Intermittent/failed CAN transceiver in a module
  • Water intrusion or corrosion in connectors or junctions
  • Aftermarket device or incorrect wiring connected to the bus
  • Failed termination resistor(s) or missing termination

Symptoms

  • Multiple modules show 'no communication' or lamp/warning messages on dash
  • Nonfunctional features controlled by modules on Bus A (e.g., ABS, BCM, ECM, infotainment)
  • Possible limp-home mode or engine won’t start if ECM/PCM lost
  • Intermittent or permanent loss of diagnostic data on scan tool
  • Illumination of multiple warning lamps

What to check

  • Connect a diagnostic scan tool; confirm U0033 and note which module(s) set the code and any related U-codes
  • Verify presence of all expected modules on the network (module list) via scan tool
  • Visually inspect CAN L wire, connectors and splices between modules for damage or corrosion
  • Check connector pins are fully seated and not pushed out or bent
  • Measure voltage at CAN H and CAN L pins with ignition ON, engine OFF
  • Measure resistance across CAN H and CAN L with ignition OFF (expected ~60 ohms)

Signal parameters

  • Idle (recessive) voltage: CAN H ≈ 2.5 V, CAN L ≈ 2.5 V (measured to chassis ground)
  • Dominant state: CAN H ≈ 3.5 V, CAN L ≈ 1.5 V (differential active state)
  • Bus differential idle ≈ 0 V (H and L equal), active differential ≈ ±2 V
  • Termination resistance (both ends present): ≈ 60 Ω across CAN H to CAN L (two 120 Ω in parallel)
  • Open-circuit: CAN L may float to supply or ground causing abnormal voltages or no differential signal

Diagnostic algorithm

  1. Read all network U-codes and note modules affected; record freeze frame and events.
  2. Inspect obvious wiring harness areas and module connectors for damage, corrosion, water, or aftermarket taps.
  3. With ignition ON (engine OFF) backprobe the reported module CAN L pin: measure voltage to chassis ground and compare to expected idle ~2.5 V.
  4. Measure CAN H at same time to confirm normal idle and differential behavior. If both absent, suspect open/termination issue.
  5. With ignition OFF, measure resistance between CAN H and CAN L at two accessible module connectors; expect ≈60 Ω. Very high/OL indicates open; very low indicates short.
  6. Isolate sections: disconnect modules one at a time (or unplug intermediate connectors) while monitoring bus resistance/communication to find where circuit opens.
  7. If a specific connector or splice is identified, repair wiring (replace pin, reterminate, or splice with solder/heat-shrink or approved crimp).
  8. If wiring and connectors check good, suspect failed module transceiver. Swap with known-good module (if applicable) or bench-test/replace module.
  9. After repair, clear codes and confirm all modules return on bus and functional. Perform road test and re-scan to ensure fault does not return.
  10. If intermittent: inspect for harness movement points, secure harness routing, and protect with loom or tape as needed.

Likely causes

  • Open/opened CAN L conductor between modules (physical break at harness or connector)
  • Bad connector pin (pulled, corroded, or pushed out) at a module with U0033 stored
  • Failed transceiver on the module that reported the code
  • Disconnected module (during service) or poor ground affecting transceiver operation

Fault status

⚠️ Status
Vehicle Communication Bus A (CAN L) open — network communication on Bus A interrupted due to open circuit in CAN low wiring, connector, or module transceiver.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

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371

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