Code
U0254
HYUNDAI
U — Network/User
Lost Communication With Remote Start Module
Views:
UK: 14
EN: 51
RU: 21
AI status
Completed
Completed
100%
Causes
- Faulty or disconnected Remote Start Module (RSM)
- Open or shorted CAN bus wiring (CAN High/Low) between RSM and network
- Poor power or ground supply to the RSM (blown fuse, bad ground, low battery)
- Corroded or loose connector pins at the RSM or intermediate junctions
- Faulty gateway or intermediary module preventing message routing
- CAN bus termination fault (missing/failed resistor) or bus short to battery/ground
Symptoms
- Remote start does not operate or is intermittent
- Warning message or lamp related to remote start or key/immobilizer
- Multiple network communication DTCs present
- Other modules report loss of data from remote start (status, commands)
- No response when attempting to communicate with RSM via scan tool
What to check
- Retrieve U0254 and any other stored/pending network DTCs with an OEM-level scanner
- Check battery voltage (should be ~12.4–12.8 V, >11 V cranking) and charging system
- Inspect fuses and relays supplying power to the RSM and related circuits
- Visually inspect RSM connectors and harness for corrosion, pin damage or disconnection
- Check for other CAN network errors or lost-communication codes (gateway/ECM/BCM)
- Attempt to communicate with the RSM using a scan tool (verify module presence and data)
Signal parameters
- Battery voltage: nominal 12–14.5 V (key ON); verify stable supply to RSM
- CAN bus idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both near mid-supply)
- CAN bus dominant states: CAN_H rises toward ~3.5 V, CAN_L falls toward ~1.5 V during frames
- If nodes present, proper differential voltage during frames ≈ 2.0 V (CAN_H - CAN_L)
- Typical CAN bus resistance (two terminators): ≈ 60 Ω total across CAN_H to CAN_L
Diagnostic algorithm
- Confirm code: Clear DTCs, cycle ignition, and re-scan to confirm U0254 returns and note freeze-frame data.
- Check battery and fuses: Verify battery charge and inspect/replace fuses or relays powering the RSM.
- Verify communication: Use a scan tool to attempt to communicate with the RSM; note if module appears on network or is absent.
- Visual/harness inspection: Inspect connector pins at the RSM and along wiring for corrosion, bent pins, or damage. Repair as needed.
- Power/ground verification: With key ON, measure module supply and ground at the RSM connector. Repair poor connections or wiring faults.
- CAN bus checks: Measure CAN_H and CAN_L at the RSM connector. If both stuck at battery/ground or not near 2.5 V, trace for short/open. Check resistance across CAN_H/CAN_L (≈60 Ω expected).
- Scope the bus (if available): Observe CAN differential waveform while another node transmits. Look for missing frames, noise, or voltage shifts.
- Isolate segments: Disconnect RSM connector and see if other modules restore normal communication (to identify bus loading or node short).
- Check gateway/routes: If RSM is on a different CAN network, verify gateway/module routing and look for gateway DTCs.
- Reprogram/replace: If wiring, power and bus are good and module still fails to communicate, update software per OEM bulletin or replace RSM and retest.
- Final verification: After repair, clear codes, perform full system test including remote start function and confirm no related DTCs return.
Likely causes
- Blown fuse or lost power/ground to the RSM
- Damaged or disconnected RSM connector or wiring harness
- Local CAN bus wiring short or open between RSM and gateway
- Failed RSM
- Module configuration or calibration fault (need reflash/programming)
Fault status
Status
Lost Communication With Remote Start Module — the vehicle network does not receive expected messages from the Remote Start Module. This may prevent remote start operation and could be caused by a module fault, wiring/power issue, or network fault.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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