The Shimano SM-EW90-B [paid link] is a central junction box used in Shimano Di2 electronic shifting systems. Designed for use with road bikes, it serves as the connection hub for the shifters, derailleurs, and battery interface, allowing precise electronic control and seamless communication across components. Installing and maintaining the SM-EW90-B [paid link] properly ensures consistent performance, minimizes electronic communication errors, and extends the life of your Di2 system.
Tools Required
- 2mm hex key
- Di2 E-Tube cables (EW-SD50)
- Shimano TL-EW02 or TL-EW300 cable tool
- Clean microfiber cloth
- Isopropyl alcohol (for cleaning contacts)
Understanding the Shimano SM-EW90-B Junction Box
The SM-EW90-B is typically mounted under the stem, acting as a distribution point for Di2 wiring. It connects to both shifters (via two or three front ports) and the main Di2 wiring harness (via a single rear port). The “B” variant offers five ports, making it compatible with dual shifters and additional accessories like climbing or sprint shifters.
Its internal circuitry ensures stable data transmission between components and houses a charging port and system indicator light, providing both functional and diagnostic features in one compact unit.
Installation of the Shimano SM-EW90-B
Installing the SM-EW90-B correctly is essential to prevent connectivity issues and to maintain the system’s waterproof integrity.
Mounting the Junction Box
The junction box is usually mounted under the stem using Shimano’s rubber mounting strap or an integrated handlebar mount. Ensure the mounting surface is clean and dry. The box should be oriented so that the ports face backward for neat cable routing.
Connecting the E-Tube Cables
Each port must be connected using Shimano E-Tube cables. The recommended process is as follows:
- Insert the Cables Using a Proper Tool
Use the TL-EW02 or TL-EW300 tool to push the E-Tube connectors into the ports. This ensures full insertion without damaging the cable ends. Avoid using fingers or metal tools, which can deform connectors. - Assign Correct Ports
The SM-EW90-B has three front-facing ports (for shifters and auxiliary controls) and two rear-facing ports (for the frame wiring harness and additional accessories). Verify each connection according to your bike’s wiring layout. - Check Cable Tension and Bends
Route cables neatly with gentle bends. Sharp angles can cause stress at the connectors and lead to intermittent communication loss. - Power-Up Check
After all connections are secure, turn on the Di2 system by pressing the button on the junction box. The indicator light should illuminate briefly, confirming successful power transmission.
Adjustment and Function Testing
Once installed, the junction box needs to be tested for proper operation.
Verifying Communication
Press and hold the button on the junction box for two seconds to activate adjustment mode. Shifting the derailleurs should cause immediate response. If there’s a delay or no movement, verify all cable connections and inspect for bent or damaged pins.
Firmware Synchronization
Connect the bike to Shimano’s E-Tube Project software via the PC interface or mobile app. This allows you to check for firmware updates, perform system diagnostics, and confirm that all components are recognized by the system. Keeping firmware up-to-date prevents synchronization errors and ensures full functionality of the SM-EW90-B.
Maintenance of the Shimano SM-EW90-B
Regular maintenance preserves both performance and reliability. The junction box itself is low-maintenance but must be kept clean and moisture-free.
Cleaning the Junction Box
Wipe the exterior regularly with a soft, dry cloth. If exposed to sweat or road grime, lightly dampen the cloth with water or isopropyl alcohol. Avoid high-pressure water or harsh cleaners, as these can compromise seals and internal circuits.
Inspecting Electrical Contacts
Unplug cables only when necessary. Each time you disconnect a cable, inspect the connector for dirt or corrosion. Use a dry microfiber cloth to remove residue. If corrosion is present, apply a minimal amount of dielectric grease to protect the contacts before reconnecting.
Cable Integrity Checks
Inspect E-Tube cables every few months. Look for cracks, pinching, or signs of strain. A damaged cable can cause erratic shifting or intermittent loss of power to the system.
Troubleshooting Common Installation Issues
Several common problems can arise when installing or adjusting the SM-EW90-B:
- No Power or No Light: Check the connection to the battery and verify the harness cable is fully seated.
- Intermittent Shifting: Likely due to loose or partially inserted E-Tube connectors. Re-seat all cables using the TL-EW02 tool.
- Flashing Indicator Light: Indicates a communication or firmware error. Connect to E-Tube Project to identify and resolve the issue.
- No Charging Response: Ensure the charging cable is correctly aligned and the system is powered. Clean the charging port if debris is present.
Regular inspection and correct installation prevent nearly all of these issues.
Optimization and Customization
The SM-EW90-B offers customization options through Shimano’s E-Tube platform. Users can reassign shift button functions, adjust shift speed, and integrate auxiliary shifters. Riders seeking faster performance or a personalized layout can use this feature to tailor the electronic interface to their riding style.
For optimal performance, keep firmware versions synchronized across all connected Di2 components. Mismatched versions can result in communication delays or partial function loss.
Comparison with Similar Models
The SM-EW90-A [paid link] is a similar model but features three ports instead of five. The “B” version is preferred for modern road setups that require multiple shifter inputs or accessories. The SM-EW90-B also provides a more flexible configuration for time-trial and aero bar setups.
When comparing with the newer EW-RS910 [paid link] bar-end junction, the SM-EW90-B remains easier to access for diagnostics and firmware updates. However, the RS910 offers a cleaner aesthetic by integrating into the handlebar end.
Compatibility Considerations
The SM-EW90-B is compatible with all Shimano Di2 E-Tube systems (both 10-speed and 11-speed generations) and works seamlessly with Dura-Ace, Ultegra, and GRX Di2 groupsets. It is not compatible with older 7970 systems, which use different wiring protocols.
Ensure all components in the setup are E-Tube compatible before installation to prevent power or communication errors.
Final Thoughts
The Shimano SM-EW90-B junction box is a critical element in the Di2 ecosystem, enabling smooth operation, diagnostic control, and charging access. Proper installation, clean routing, and regular maintenance ensure long-term reliability. Riders who take time to set it up carefully will enjoy flawless shifting and minimal troubleshooting throughout their bike’s lifespan.