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Home / DTC / U0028 — Vehicle Communication Bus A

U0028 — Vehicle Communication Bus A

Detailed page for trouble code U0028.

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59brands
11,925generic
22,612specific
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Code

U0028

HYUNDAI U — Network/User

Vehicle Communication Bus A

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

Causes

  • Open or short in CAN/vehicle-bus A wiring harness
  • Damaged or corroded connector(s) at ECU(s) or splice(s)
  • Failed module (ECU) driving or loading the bus
  • Failed/missing termination resistor(s) or incorrect termination
  • Low battery voltage or poor battery/ground connections affecting bus transceivers
  • Aftermarket device or radio interfering with the bus

Symptoms

  • Multiple control modules show communication errors or are inoperative
  • Warning lights or multiple DTCs present (communication-related)
  • Intermittent or permanent loss of functions controlled by modules on Bus A (instruments, ABS, HVAC, etc.)
  • No response from one or more modules with scan tool on Bus A
  • Vehicle may not start or run properly if powertrain modules affected

What to check

  • Scan all modules; record U-codes and other related module faults
  • Record freeze-frame and module responses to determine which modules are not responding
  • Visually inspect CAN wiring harness and connectors for damage, corrosion, or aftermarket splices
  • Check battery voltage and main ground connections; restore full battery voltage before testing
  • With ignition ON, use a scan tool/communication tester to see if Bus A messages are present
  • Measure CAN bus resistance between CAN_H and CAN_L with ignition ON (expected ~60 Ω)

Signal parameters

  • With ignition ON, key ON engine OFF: CAN_H ≈ 2.5–3.5 V (recessive ≈2.5 V)
  • With ignition ON, key ON engine OFF: CAN_L ≈ 1.5–2.5 V (recessive ≈2.5 V; note manufacturer differences)
  • Recessive differential (CAN_H − CAN_L) ≈ 0–0.2 V; dominant differential ≈ 1.5–2.5 V during bus activity
  • Bus termination resistance (CAN_H to CAN_L) with power ON ≈ 60 Ω (two 120 Ω terminators in parallel)
  • Signal waveform: clean digital differential square waves; heavy noise, clipped or flat lines indicate fault

Diagnostic algorithm

  1. Connect a capable scan tool and retrieve all codes and freeze frame data from every module; save results
  2. Confirm battery voltage ≥ 12.4 V and good chassis and engine ground connections before testing
  3. Visually inspect the entire Bus A harness routing and all module connectors for damage, corrosion, or aftermarket connections; repair obvious physical damage
  4. Measure DC resistance between CAN_H and CAN_L (ignition ON). If not ≈60 Ω, inspect for missing/burnt terminators or unwanted parallel loads
  5. With ignition ON, measure CAN_H and CAN_L voltages at a convenient connector. Compare to expected ranges. If voltages are out of range, trace toward the first connector/module showing the abnormal reading
  6. If voltages look normal but communication is missing or noisy, use an oscilloscope on differential pair to view waveforms while operating scan tool; look for noise, dominant states, or no activity
  7. Disconnect suspected modules (one at a time) from the bus and re-check communication and resistance to find a module that, when removed, restores the bus
  8. If a specific module is identified, verify its supply voltage and ground at the module, inspect its connector pins, and replace or repair as required per manufacturer procedure
  9. Repair damaged wires, corroded connectors, or replace termination resistors. After repairs, clear codes and verify restoration of normal bus traffic and operation
  10. If harness and connectors are good and disconnecting modules does not isolate the problem, consider ECU/module replacement only after confirming the module is at fault and not caused by wiring or power/ground issues

Likely causes

  • Corroded connector or poor ground at one of the control modules on Bus A
  • Open/short in CAN_H or CAN_L wiring (accident repair, chafing)
  • Failed ECU transceiver on one module causing bus load or contention
  • Missing or damaged termination resistor (open or short)

Fault status

⚠️ Status
Communication fault on Vehicle Communication Bus A — messages missing or bus electrically impaired (open/short/no activity).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-3 hours

Similar codes

U0001 U0027 U0073 U0100 U0121
371

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