U0074

Code

HYUNDAI U — Network/User

Control Module Communication Bus “B” Off

Brand: HYUNDAI

Type: U — Network/User

Views: UK: 13 EN: 22 RU: 18

AI status

Completed

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Page language: EN

Battery or charging system low voltage or intermittent supply
Blown fuse or poor ground affecting one or more modules on Bus B
Open, short to ground, or short to voltage in CANH/CANL wiring for Bus B
Faulty control module (module transceiver or internal failure) on Bus B
Missing or failed termination resistor(s) at bus ends
Corroded or loose connectors or poor pin contact at module connectors or junctions

Malfunction Indicator Light (MIL) or network-related warning messages
Loss of function for systems on Bus B (examples: infotainment, ABS, airbags, body modules — vehicle-specific)
Scan tool shows U0074 and may show other U-codes (lost communication codes)
No live data from modules on Bus B when scanned
Intermittent or total loss of features that rely on that bus

Record all stored U-codes and freeze-frame data; note which modules report missing
Check battery voltage and charging system; verify steady 12 V (key on and cranking)
Inspect and verify fuses, fusible links, and main grounds related to Bus B modules
Visually inspect connectors, wiring looms, and splice/junction points for damage or corrosion
Use a scan tool to list modules present on each network and note which are unresponsive
Measure resistance across CANH and CANL at two end points (with power off) to confirm ~60 Ω termination

Recessive (idle) voltage: CANH ≈ 2.5 V, CANL ≈ 2.5 V (each referenced to vehicle ground)
Dominant state: CANH rises toward ≈ 3.5 V while CANL falls toward ≈ 1.5 V; differential typically ≈ 2.0 V during dominant bits
Termination resistance: approximately 60 ohms measured across CANH and CANL (two 120 Ω resistors in parallel)
Typical bus speeds vary by vehicle and network (commonly 500 kbps for high-speed CAN); confirm vehicle-specific baud rate before detailed waveform analysis

Retrieve and document all codes; note any other U-codes or module-specific lost-communication codes.
Verify battery voltage and ground quality. Charge or maintain battery at proper voltage during testing.
Check fuses and power feeds to modules on Bus B and to any gateway/can hub; repair faults.
Visually inspect wiring and connectors for damage, corrosion, or loose pins on modules that should be on Bus B.
With ignition ON (engine OFF), measure CANH and CANL voltages at a known connector. Expect ~2.5 V idle. If voltages are absent, suspect open power/ground or major wiring fault.
With power off, measure resistance between CANH and CANL at two ends of the bus to confirm proper termination (~60 Ω).
Use an oscilloscope on CANH/CANL with vehicle operating or while communicating to observe waveform integrity (search for missing frames, dominant/continuous levels, excessive noise).
Isolate the fault by disconnecting modules on Bus B one at a time (or disconnect suspected modules) while monitoring the bus to see when communication returns or when fault changes.
Repair wiring (open/short/poor connector) or replace the faulty module or gateway as identified. Replace missing/failed termination resistors if required.
After repair, clear codes, verify all modules reappear on the network, perform any required module programming or relearn procedures, and road-test to confirm fault does not return.

⚠️ Status

Control Module Communication Bus "B" Off — No valid communication detected on CAN Bus B. Network segment appears inactive or interrupted.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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U0074 — Control Module Communication Bus “B” Off