U0299

Code

HYUNDAI U — Network/User

Lost Communication With DC to DC Converter Control Module “B”

Brand: HYUNDAI

Type: U — Network/User

Views: UK: 15 EN: 38 RU: 13

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Page language: EN

DTC U0299 stored; related CAN‑communication DTCs may also appear
Battery charging or auxiliary 12V system warnings (hybrid/EV systems)
Reduced functionality of systems fed by DC‑DC converter (12V accessories, HVAC, infotainment)
Possible illumination of malfunction indicator or warning messages on dash
Intermittent loss of systems or limp-home mode in severe cases

Connect a diagnostic scanner; read U0299 and any accompanying codes, freeze frame and occurrence counts
Verify battery voltage is within specification (engine off and cranking conditions as required)
Inspect fuses/fusible links and power/ground circuits to DC‑DC converter module B
Visually inspect connectors, pins and wiring harness for corrosion, damage or water intrusion
Check for CAN bus activity with a scan tool: are messages from the DC‑DC converter present?
Measure CANH and CANL voltages and bus resistance (termination) with key on, engine off

CAN bus idle voltages: CANH ≈ 2.5 V, CANL ≈ 2.5 V (recessive state)
CAN dominant voltages: CANH ≈ 3.5 V, CANL ≈ 1.5 V (differential ≈ 2 V)
Expected total bus termination: approximately 60 Ω measured end‑to‑end (two 120 Ω terminations in parallel)
Network data rate depends on vehicle (commonly 500 kb/s or 250 kb/s); verify correct baud rate for module
Module power supply: presence of battery/ignition 12 V (verify per wiring diagram)

Use a capable scan tool to record U0299 and related codes, note freeze frame and VIN‑specific info.
Confirm vehicle battery voltage and charge state; charge battery if low and retest.
Inspect and verify fuses and power/ground pins at the DC‑DC converter control module B connector.
With ignition on, check CAN bus activity using the scan tool: look for messages from the DC‑DC converter and gateway.
Measure CANH and CANL voltages at the module connector; compare to expected idle and dominant levels.
Measure resistance across CANH‑CANL at two bus ends (approx. 60 Ω). If open or out of range, trace wiring and check termination resistors.
Visually inspect and backprobe connectors; repair any damaged wiring, pins or corrosion found.
If wiring and power/ground are good but no communication, check upstream gateway/module that routes messages; verify it is powered and communicating.
If network and gateway are OK, replace or reprogram the DC‑DC converter control module per manufacturer procedures (verify software level).
After repair, clear codes and roadtest; verify no reoccurrence and that related systems operate normally.

No battery power or ground at DC‑DC converter control module B (fuse blown / connector loose)
Broken/disconnected CAN‑H or CAN‑L between module B and gateway/ECU
Short to battery or ground on CAN lines or network termination problem
Module internal failure or processor fault
Network interference from a different module or aftermarket device

⚠️ Status

Lost Communication With DC to DC Converter Control Module "B" — no CAN messages received from module B

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours

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U0299 — Lost Communication With DC to DC Converter Control Module “B”