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Home / DTC / U1500 — Wakeup Line Short Circuit To Ground | MOST bus communication lost during extended diagnostic session.

U1500 — Wakeup Line Short Circuit To Ground | MOST bus communication lost during extended diagnostic session.

Detailed page for trouble code U1500.

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U1500

HYUNDAI U — Network/User

Wakeup Line Short Circuit To Ground | MOST bus communication lost during extended diagnostic session.

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

Causes

  • Damaged or chafed wiring harness causing wakeup line to contact chassis ground
  • Corroded, bent, or pushed-back connector pin creating a direct ground
  • Failed module with internal short on the wakeup/wake line
  • Aftermarket audio, amplifier, or alarm device tied into wake/sleep circuit incorrectly
  • Water intrusion in connector or module causing low-resistance path to ground
  • Faulty termination or bus interface circuit in MOST/electronics module

Symptoms

  • Infotainment, navigation, or amplifier modules not waking or not visible to diagnostic tool
  • Audio system silent or erratic; some MOST devices not present in module list
  • Extended diagnostic session shows MOST bus communication lost or bus off
  • Battery drain in some cases if circuit stuck active, or inability to wake modules normally
  • Intermittent operation — functions return when harness moved or connectors reseated

What to check

  • Retrieve full network status and freeze frame with a capable scan tool; note which modules are not communicating
  • Visually inspect wiring, connectors, and ground points for damage, corrosion, moisture, or aftermarket splices near the infotainment, amplifier, gateway and junction boxes
  • With ignition OFF, measure resistance from the suspected wakeup pin to chassis ground at the harness connector — expect very high resistance; low resistance indicates a short
  • Backprobe wakeup line with a multimeter while toggling ignition/wake commands from scan tool — verify expected voltage transitions (see signal_params)
  • Unplug suspected modules (amplifier, head unit, gateway) one at a time to see if the short clears and comms return — isolate the module causing the short
  • Inspect and test relevant fuses and relays for the infotainment/ MOST power and wake circuits

Signal parameters

  • Wakeup line expected idle: approximately battery voltage (11–13.5 V) when not driven low (varies by model)
  • Wake pulses: brief transitions or wakes sent by gateway/head unit when ignition or remote wake occurs (voltage rises/pulses from 0 to Vbat)
  • Short condition: wakeup conductor measured
  • Normal open-circuit resistance from wake line to ground: kilo-ohms to mega-ohms (no continuity)
  • MOST optics: optical link activity LED on modules (if visible) or diagnostic status should indicate active optical link when awake

Diagnostic algorithm

  1. Safety first — park vehicle, engage parking brake and follow workshop safety. If work requires removing batteries or airbags, isolate battery per vehicle procedure.
  2. Connect a scan tool that supports Hyundai MOST networks. Record U1500 and any other U-codes, module presence, and freeze frame data.
  3. Confirm battery voltage is healthy (12.0–13.5 V). Low battery can affect wake behavior and give misleading results.
  4. Perform a visual inspection of harnesses and connectors for the head unit, amplifier, gateway, junction boxes, and any common splices. Pay attention to grommets and areas where harness flexes.
  5. With ignition OFF, disconnect the connector for the suspect module(s). Measure resistance between wakeup pin and chassis ground at the harness side. A resistance
  6. If a short is present, disconnect modules one at a time (head unit, amplifier, gateway) and remeasure to find which segment clears the short. When disconnecting, ensure connectors are fully seated/latched to avoid false readings.
  7. If disconnecting a module clears the short, suspect the module or its internal harness. Inspect its connector pins for corrosion or pin damage. Substitute a known-good module if available to confirm.
  8. If no single module isolates the short, trace the harness physically along the vehicle path and check for chafing, pinched insulation, or contact with body/chassis at high-stress points.
  9. Backprobe the wake line with ignition OFF then ON and have a helper wake the vehicle with scan tool commands; verify voltage transitions and presence of wake pulses per signal_params.
  10. Repair wiring or connector damage: repair or replace harness sections, replace corroded connectors, and apply proper seals. Replace faulty module only after harness and connector faults are cleared.
  11. After repairs, clear codes, perform a full network scan to confirm all MOST devices come online and run any relearn or software updates required by Hyundai.
  12. Notes: take care when probing connectors — if high-voltage or hybrid systems are present, follow vehicle-specific isolation procedures.

Likely causes

  • Shorted wakeup (wake/sleep) conductor in harness near junctions or body harness grommets
  • Pin shorted to chassis in infotainment or amplifier connector (common at amplifier or gateway module)
  • Failed head unit, amplifier, or gateway module pulling the wake line to ground internally
  • Poor repair or splice where insulation is missing, allowing contact with ground
  • Connector corrosion or foreign material bridging the wake line to ground

Fault status

⚠️ Status
Wakeup line shorted to ground detected on MOST/infotainment network. MOST bus communication lost during extended diagnostic session; modules may not wake or be visible to diagnostic tool.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0100 U0073 U0140 U0155
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Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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