How to Diagnose and Fix Noisy Set-Up on Your Shimano SM-EW90-A

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The Shimano SM-EW90-A [paid link] Junction A is a compact and critical component in the Di2 electronic shifting system. It serves as the main interface between the rider and the bike’s electronic drivetrain, managing communication between shifters, derailleurs, and the battery. While Di2 systems are known for their precision and reliability, some riders experience unwanted noise during operation—typically clicking, buzzing, or intermittent connection sounds. This guide explains how to diagnose and fix noisy issues on your Shimano SM-EW90-A [paid link] to ensure silent, flawless electronic shifting.

Understanding the SM-EW90-A Junction Box

The SM-EW90-A is part of Shimano’s Di2 E-Tube system and connects to multiple components using E-Tube wires. It typically mounts under the stem or handlebar, acting as a communication hub. It features three E-Tube ports, allowing connections for the left shifter, right shifter, and the main junction leading to derailleurs and the battery.

Because of its central role, even a minor wiring or mounting issue can cause electronic noise or inconsistent performance. Noise may stem from physical vibration, cable tension, or even loose internal connections within the junction.

Tools Required

  • 2.5 mm and 3 mm hex wrenches
  • Shimano E-Tube wire plug tool (TL-EW02)
  • Soft microfiber cloth
  • Isopropyl alcohol (for cleaning contacts)
  • Di2 diagnostic software (optional for advanced checks)

Step 1: Identify the Source of the Noise

Before disassembling or adjusting, determine where the sound originates. Noise around the SM-EW90-A may come from:

  • Loose mounting under the stem or handlebar.
  • E-Tube wires rattling inside the bar or frame.
  • Minor gaps between connectors and junction ports.
  • Electronic interference or connection faults.

Begin by lightly tapping the junction and nearby components while the bike is stationary. If the sound replicates, it’s likely mechanical rather than electrical. If the noise only occurs during shifting, investigate the electronic connection integrity.

Step 2: Check Mounting Tightness and Placement

The SM-EW90-A mounts using a rubber strap or a clip-on bracket, depending on your setup. If it’s slightly loose, vibration from the road or cables can amplify noise.

  1. Loosen the mounting strap using the hex wrench.
  2. Clean the mounting surface and ensure no debris sits between the junction and handlebar.
  3. Reinstall the junction snugly—tight enough to prevent movement but not overly compressed.

Avoid overtightening, as excessive pressure can deform the housing or strain the E-Tube ports, leading to poor connections and additional noise.

Step 3: Inspect and Reseat E-Tube Connectors

A common cause of buzzing or clicking sounds is a partially seated E-Tube wire. Over time, vibrations can cause connectors to back out slightly, disrupting contact points.

  • Use the Shimano TL-EW02 tool to gently remove each connector from the junction.
  • Inspect each plug for dirt, corrosion, or wear.
  • Wipe both the plug and the port with a microfiber cloth dampened with isopropyl alcohol.
  • Reinsert each connector until you hear or feel a distinct “click.”

Each port should feel secure with no movement. If one feels loose or inconsistent, test it with another cable to rule out a damaged connector.

Step 4: Check Internal Cable Routing

Internal routing can also create noise, particularly if E-Tube cables contact the handlebar walls or move inside the frame.

  • Gently shake the handlebars while listening for rattling sounds.
  • If cables are internal, apply light foam sleeves or cable dampers inside the bar.
  • Ensure all cables have sufficient slack to avoid strain during steering or braking.

For external routing, make sure E-Tube wires are firmly secured with small cable ties or silicone sleeves to prevent vibration.

Step 5: Run a Diagnostic Check (Optional)

If mechanical adjustments do not resolve the issue, a firmware or connection error may be responsible. Use Shimano’s E-Tube Project software to connect your bike to a computer.

  • Inspect for any error codes or unstable voltage signals.
  • Ensure all firmware versions are up to date, particularly for the junction box and derailleurs.
  • Clear any faults and retest the shifting system.

While not directly related to noise, unstable connections can cause electronic clicking or repetitive relay sounds inside the junction.

Step 6: Test Shifting Under Load

After completing mechanical and electronic checks, test the setup on a stand and on the road. Perform multiple shifts across both derailleurs. Listen for any repeating sound patterns.

If noise persists only under load, check the front junction’s interaction with nearby cables or the handlebar tape. In some cases, simply repositioning or re-wrapping the cables around the bar resolves residual sounds.

Step 7: Long-Term Maintenance Tips

To keep your SM-EW90-A quiet and reliable:

  • Clean and inspect E-Tube connections every 3–6 months.
  • Avoid sharp bends in wiring, which can strain ports and cause intermittent contact.
  • Keep firmware updated to ensure stable communication between all Di2 components.
  • Store the bike indoors to prevent moisture-related corrosion within the junction box.

Common Mistakes That Cause Persistent Noise

Riders often overlook small issues that lead to recurring noise:

  • Mounting the junction box too tightly against a carbon handlebar, creating resonance.
  • Forgetting to reseat cables after changing handlebar tape.
  • Using non-Shimano E-Tube wires, which may not fit securely.
  • Leaving excessive cable slack near the stem, causing micro-vibrations.

Each of these can be avoided through regular inspection and proper installation technique.

When to Replace the SM-EW90-A

If the junction continues to make clicking or electrical noises despite all corrections, internal circuitry may be failing. Signs of a failing unit include:

  • Random LED flashing without button input.
  • Temporary shifting loss despite intact wiring.
  • Audible relay clicking from within the junction housing.

In such cases, replacement is recommended. The SM-EW90-A is a serviceable part and easily swapped using standard Di2 wiring procedures.

Conclusion

A noisy Shimano SM-EW90-A often points to loose connections, poor cable routing, or improper mounting rather than internal faults. Through systematic inspection, cleaning, and proper installation, the junction box can operate silently and reliably for years. Regular maintenance, combined with attention to connection integrity, ensures your Di2 system performs with the seamless precision Shimano intended.