U0008

Code

HYUNDAI U — Network/User

High Speed CAN Communication Bus (-) High

Brand: HYUNDAI

Type: U — Network/User

Views: UK: 13 EN: 14 RU: 24

AI status

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Page language: EN

Damaged or shorted CAN_L wiring (short to battery or other supply)
Open or high-resistance connection on CAN_L (corrosion, broken conductor, poor pin contact)
Failed or internally shorted control module on the CAN bus
Missing or incorrect termination (open/missing 120 Ω terminators)
Intermittent connector contact or water ingress
Incorrect aftermarket device or improper splice on the CAN network

Multiple modules report loss of communication or intermittent behavior
Instrument cluster warnings for communication/network faults
Disabled vehicle functions that rely on bus messages (ABS, ESC, engine, transmission, gateway messages)
Erratic module operation or lights on dash
Possible poor starting or no-crank if ECM/PCM loses network access

Scan all modules with a capable OEM or advanced scan tool; record all U-codes and freeze-frame data
Visually inspect all CAN-related connectors, harnesses and module grounds for corrosion, damage, water entry, or loose pins
With ignition ON (engine off) measure voltage between CAN_L and chassis ground and between CAN_H and chassis ground
Measure resistance across CAN_H to CAN_L with ignition OFF — expected network termination (see signal parameters)
Wiggle or gently stress wiring/connectors while monitoring bus voltage and network messages for changes
Disconnect suspected modules one at a time (or isolate sub-networks) to identify a failing module causing the high voltage

CAN bus idle (recessive) voltage: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both near mid-supply)
CAN dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
High fault condition (CAN_L abnormally high) — CAN_L above typical recessive ~2.5 V (may approach CAN_H levels or battery voltage when shorted)
Typical high-speed CAN bit rate: 500 kbps (some networks 250 kbps or 125 kbps — verify OEM)
Termination: two 120 Ω resistors (one at each end) giving ~60 Ω total measured across CAN_H to CAN_L with ignition OFF

Verify DTC and related U-codes with a scan tool; note occurrence and freeze-frame. Check for stored vs active.
Inspect visible CAN wiring, connectors, gateway module, and module ground points for damage, corrosion, or moisture. Repair any obvious faults.
With ignition ON (engine off), measure CAN_H and CAN_L to chassis ground and CAN_H to CAN_L. Compare to expected signal parameters. If CAN_L is high vs expected, isolate cause.
With ignition OFF, measure resistance between CAN_H and CAN_L at a convenient connector — expect ~60 Ω. If open or much higher, check for missing termination. If very low or shorted to battery, check for short.
Use an oscilloscope (preferred) to view CAN_H/CAN_L waveforms while operating CAN devices or cranking; look for stuck-high levels, noise, or missing differential signals.
To isolate a faulty module, disconnect modules (starting with non-critical or easily accessed nodes) one at a time and re-check bus voltages/waveforms until the fault clears. Reconnect to find the offending module.
If a short to battery or chassis is indicated, trace wiring back from the fault location, inspect for pin-to-pin contact, aftermarket device taps, or damage from repairs/accidents.
Repair or replace damaged wiring, connectors, termination resistors, or faulty control module(s). After repair, clear codes and perform network communication verification and a road/test cycle to confirm repair.

⚠️ Status

High-speed CAN bus (CAN_L) voltage above normal range — network communication errors detected.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-3.0 hours

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