Toggle Side Panel

Shopping Cart

No products in the basket.

Shopping Cart

No products in the basket.

Close search
Home / DTC / U0018 — Medium Speed CAN Communication Bus (-) shorted to Bus (+)

U0018 — Medium Speed CAN Communication Bus (-) shorted to Bus (+)

Detailed page for trouble code U0018.

34,649codes
59brands
11,925generic
22,724specific
All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
Reset
Code

U0018

HYUNDAI U — Network/User

Medium Speed CAN Communication Bus (-) shorted to Bus (+)

Brand: HYUNDAI
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Wiring short between CAN− and CAN+ (pin-to-pin short)
  • Chafed or damaged harness where conductors contact each other or a conductive body
  • Faulty connector with bent pins or conductive contamination
  • Aftermarket accessory or module incorrectly wired into the CAN bus
  • Internal short inside a control module or ECU
  • Failed termination resistor or incorrect termination

Symptoms

  • Multiple modules on the medium-speed CAN bus report communication errors or go into limp/fault mode
  • Intermittent or complete loss of functions controlled by that network (e.g., body controls, gateway functionality)
  • Dashboard warning lights (CAN, ABS, airbag, instrument cluster faults depending on network)
  • Erratic behavior of modules on the affected bus
  • Freeze or bus-off state for one or more modules

What to check

  • Read and record all U-codes and related module fault memories with a capable scan tool
  • Visually inspect CAN wiring harness and connectors for damage, corrosion, or water intrusion
  • Check connectors for bent pins, debris, or signs of arcing
  • Measure resistance between CAN+ and CAN− with ignition off (look for short)
  • Measure resistance from each CAN line to battery positive and ground (looking for unintended shorts)
  • Check termination resistance across CAN+ and CAN− (typical networks show ~60 Ω if two 120 Ω terminators present)

Signal parameters

  • Typical recessive voltages (typical high-speed CAN reference): CAN_H and CAN_L near mid-rail (~2.5 V) with small differential (varies by vehicle)
  • Dominant state: CAN_H rises and CAN_L falls producing a differential of ~1–2 V (varies by system type)
  • Expected resistance between CAN+ and CAN− with network intact and two terminators: ~60 Ω (two 120 Ω terminators in parallel). Some medium-speed networks may use different termination values—check vehicle spec.
  • With ignition off, open-circuit between CAN lines except through module inputs (no direct short to battery or ground)

Diagnostic algorithm

  1. Record all current and pending codes from all modules; note freeze frame and capture data.
  2. Attempt to reproduce the issue; observe which modules report communication loss.
  3. Visually inspect the entire medium-speed CAN harness and connectors, paying attention to routes through doors, harness grommets, body seams, and near moving parts.
  4. With ignition off, measure continuity between CAN+ and CAN−. A near-zero ohms reading indicates a direct short. If present, isolate by sectioning harness (disconnect connectors) to find which segment shows the short.
  5. Measure resistance from each CAN line to battery positive and ground to locate shorts to power or chassis.
  6. Disconnect suspected modules (one at a time) and check if the code clears or bus behavior returns to normal. If disconnecting a module clears the fault, inspect/remove that module for internal short or replace if confirmed faulty.
  7. If no module isolates the short, systematically disconnect harness sections (start near gateway/junction) and retest to narrow the shorted segment.
  8. Use an oscilloscope or CAN analyzer on CAN+ and CAN− to verify waveform integrity and look for sustained dominant state or abnormal voltages.
  9. Repair wiring or connector faults (replace damaged sections, clean/replace connectors, repair chafing areas). Replace modules only after wiring is confirmed good.
  10. After repair, clear codes and perform a road or system test to verify the network operates normally and codes do not return.

Likely causes

  • Physical wiring damage (abrasion, pinch, rodent chew) creating a direct short
  • Corroded or contaminated connector causing bridging between CAN lines
  • Faulty replacement or aftermarket module wired across CAN+ and CAN−
  • Internal short in a nearby control module

Fault status

⚠️ Status
Medium-speed CAN bus negative conductor is shorted to the positive conductor — communication on that network is impaired.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.0 hours

Similar codes

U0073 U0017 U0100 U0101 U0121
371

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

HYUNDAI

Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

Report

Harassment or bullying behavior
Contains mature or sensitive content
Contains misleading or false information
Contains abusive or derogatory content
Contains spam, fake content or potential malware

Block Member?

Please confirm you want to block this member.

You will no longer be able to:

  • See blocked member's posts
  • Mention this member in posts
  • Invite this member to groups
  • Message this member
  • Add this member as a connection

Please note: This action will also remove this member from your connections and send a report to the site admin. Please allow a few minutes for this process to complete.

Report

You have already reported this .