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Home / DTC / U1981 — Timeout Multimedia CAN Message(Vehicle Speed)

U1981 — Timeout Multimedia CAN Message(Vehicle Speed)

Detailed page for trouble code U1981.

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U1981

HYUNDAI U — Network/User

Timeout Multimedia CAN Message(Vehicle Speed)

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

Causes

  • Faulty or non‑transmitting vehicle speed source (ABS/BCM/PCM).
  • Open, short, or high resistance in the CAN wiring between speed source and multimedia unit.
  • Loose, corroded, or disconnected connectors at multimedia unit, BCM/ABS or gateway module.
  • CAN bus termination or wiring damage (short to battery/ground).
  • Multimedia unit software mismatch or firmware bug.
  • Faulty multimedia/head unit or gateway module that does not read the bus.

Symptoms

  • Multimedia/navigation does not show vehicle speed or speed‑based features disabled.
  • Navigation speed‑based guidance erratic or unavailable.
  • Pop‑up warnings or error message on infotainment screen indicating lost vehicle speed.
  • Related features that depend on vehicle speed (speed-dependent audio leveling, camera overlays) may not function.
  • DTC present in multimedia/gateway module; may be intermittent.

What to check

  • Read and record freeze frame and full DTC list from multimedia, BCM, ABS and gateway modules with a capable scan tool.
  • Check whether the U1981 code is current or intermittent; note any other communication codes.
  • Use a CAN‑bus capable scanner/diagnostic tool to monitor for the Vehicle Speed CAN message on the multimedia/gateway bus while turning ignition on and during a short drive.
  • Visually inspect connectors, pins and wiring for the multimedia unit, gateway, ABS/BCM and related splice points for corrosion, damage or poor seating.
  • Check fuses and power/ground at multimedia unit and at likely sender modules (ABS/BCM).
  • Measure CAN_H and CAN_L voltages at the multimedia connector (with ignition ON) and compare to expected idle values.

Signal parameters

  • Message: Vehicle Speed (manufacturer name varies; may be transmitted by ABS, BCM or gateway).
  • Typical bus: vehicle high‑speed CAN or gateway CAN (manufacturer dependent).
  • Typical frequency: periodic (commonly 1–20 Hz depending on function); should be consistently present when ignition is ON and vehicle moving.
  • Data: speed encoded in specific message bytes (manufacturer‑specific — consult OEM documentation for bit/byte mapping).
  • Physical levels: CAN_H and CAN_L idle around ~2.5 V each; dominant state shifts differential voltage (use proper CAN test tools).

Diagnostic algorithm

  1. Confirm U1981 is stored in multimedia/gateway and note any related codes in other modules. Do not replace parts yet.
  2. With ignition ON, use a CAN‑capable scan tool or oscilloscope at the multimedia connector to check for the Vehicle Speed message. Verify frequency and contents when vehicle is stationary and while driving slowly. If message is present on another bus, check gateway routing.
  3. If message is absent, trace wiring from the expected transmitter (ABS/BCM/PCM) to the gateway and multimedia unit. Inspect connectors and pins for corrosion/damage and repair as needed.
  4. Check power and ground circuits to the multimedia, gateway and the transmitting module(s). Replace/repair blown fuses or bad grounds.
  5. If CAN physical layer voltages are out of range (open, short, or missing termination), isolate and repair wiring fault. Verify termination resistors at ends of the high‑speed CAN bus.
  6. If message is present on the CAN bus but multimedia does not receive it, suspect head unit or gateway internal fault — check software version and available TSBs; perform available software reflash or module reset per OEM procedure.
  7. If message is absent at the source module, diagnose that module’s inputs (vehicle speed sensor signals, wheel speed sensors, PCM data) and repair as needed. Check for related P codes (e.g., VSS faults).
  8. After repairs, clear codes and perform a test drive to confirm message presence and that U1981 does not return. Document repairs and update module software if recommended.

Likely causes

  • Loose/corroded connector at multimedia head unit or gateway.
  • Faulty multimedia head unit not receiving/processing CAN messages.
  • Defective sender module (ABS, BCM, PCM) that normally transmits vehicle speed.
  • CAN bus wiring damage or missing termination resistor.
  • Software/firmware incompatibility between modules.

Fault status

⚠️ Status
Multimedia did not receive the expected Vehicle Speed CAN message within timeout period.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

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371

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